Cooling the 1KZ-TE motor:

[tommi786]

Sounds good! Thanks.

 

[tommi786]

Update after several weeks.....

Gearbox was dropped and seal changed. That was a quick job other than the pain removing the box.

However, as it was down, checked the transfer box and both output bearings seemed to be whining really badly. Opened that up and what a mess inside. Almost all the bearings including high speed needle bearings were gone. Order time... nothing available in Kenya so on to Dubai and ordered parts in. A week for that and another two to close the transfer box.

Whist at it also changed all the ATF and the filter.

All back together then. Suspected dodgy new rad out and old genuine Toyota one in after a comprehensive flush and leak test. Changed Thermostat to a 76 degree one. And put in new Toyota red coolant.

ATF cooler arrived. Installed that. Also took apart viscous fan and refilled with Silicon oil. The screws really bothered me. Replaced them all with Allan Key Bolts.

All done, water temp now sits at 80 except when really pushing when it climbs marginally to 85.

Installed an oil temp gauge for the ATF (used a threaded tee in the oil pipe the one going up into the cooler in which the sender screwed in. That's sitting at 80 when cruising. Tested in a trying hill at slow speeds and it climbed to around 102. I am guessing that is normal but comments welcome here.

Longer test drive tomorrow........

I cannot do anything else to the cooling system I guess so here is fingers crossed that All will stay well now.

Hope my bank account recovers soon.....!

 

[Jack VZJ90]

Hi Bob,
Maybe i'm mistaken, but i don't read about installing a new radiator ?
My toyota is a 3.4 V6, and i installed a new radiator after 300.000 km for the same reasons as yours.
It was clogged at the inside.
Good prevention from toyota would be announcing to change radiators after 250.000 km.
Saves a lot of cracked heads and blown hoses.
Also your heather core in the car can indicate a clogged system, when heather isn't as hot as before !!

 

[MarkW]

when heather isn't as hot as before !!

The Heather I know has never been hot

 

[Jack VZJ90]

The Heather I know has never been hot

Let me guess ....
Your wife's name is heather ..... i ment heater !
LOL
Happens when first language is dutch .......
LOL

 

[MarkW]

I guessed it was a typo but it was too good to resist

No wife though

 

[tommi786]

Had a longer run yesterday. Behaved well. Water temp did not go beyond 88 even when pulling up the Rift Valley escarpment road. On this section with number of trucks to overtake going uphill the AT temp went as high as 110 but would drop to 95ish when going steady and to 80 as overdrive locked in. I am guessing this is normal and 110 is not too high for short bursts. The factory AT temp light stayed off.

 

[Sandcruiser]

Thanks for the responses, guys. I would really like to get to the bottom of my problem.

The Radiator was new from Milners last June. It looked OK and when I flush it out with a hose the water runs through quite easily. I wouldn't have thought it was preventing the water pump from doing its stuff as it won't be passing anything until the thermostat is open.

The water pump was also replaced last year after the original started to leak. Its not a Toyota part (I just rushed to my local MF and took what they offered). It looked identical to the one that came out - but that may not have been a Toyota one either.

Here they are, side by side:


View attachment 48867


I had wondered if the block had some obstruction in it - one used to hear stories of rags being left in or the original sand-casting core formers not being removed completely but I couldn't detect anything with a probe down the cooling holes. I didn't want to start removing core plugs

Initially, I had decided to modify the standard thermostat. I removed the 'jiggler' and bored the hole out to 5mm to let some coolant circulate constantly. However, I fitted the 76 deg 'stat instead so I don't know what effect that might have had.


View attachment 48868



I'll keep working on the problem and will report back. I have a horse-towing job lined up for April 11th so I'll be interested to see how it performs then.

Bob.

Try removing the centre of thermostat.. replace thermostat ring back in its original position as this will allow maximum water flow while keeping enough water retention in cooling system.....I myself have suffered similar problems in outback Australia (my back yard) and found by removing centre of thermostat and reinserting outer ring back into it,s housing kept temperature at good reasonable temp...I hope this maybe helpfull keep cruisin....Kev....

 

[pyemaster]

Just to add my experience to the thread.

I've a 94 Hilux Surf with the 1KZTE with the auto box. Following an indy garage mess up with not properly bleeding the system after a routine coolant change shortly after buying it, I had a new head, gasket, head bolts, water pump, pulleys, belts, thermostat, rad cap, hoses, re-cored original rad, etc all fitted for peace of mind. That was in 2012.

After a year of seeing slightly increased temps on steep hills, I also had a standalone ATF cooler fitted, bypassing the rad, which did the job very nicely, including some pretty hectic mountain climbs in Spain. That was in 2014.

On a recent trip travelling up from Innsbruck in Austria up to Seefeld (an absolutely monumental climb) with the engine working hard I started to see the temperature climb just above halfway on the stock gauge, before settling back down quickly when easing off the throttle. No coolant lost, just a hardworking, hot engine showing so on the gauge.

For added peace of mind, on coming home I had the viscous clutch fluid replaced with 10,000, advanced the fan clutch bite point forward on the adjusting screws, upgraded to a 10-blade Hella fan, fixed my shroud (a little loose at a crack near the bottom) and flushed / reverse flushed the whole coolant system before changing.

On inspection - despite all the work done only 5 years ago - there was still a fair amount of rusty crud which had circulated in the system and found its way to the cap. I think this is because when all the work was done in 2012 they probably changed the coolant but didn't flush a lifetime of it out properly when doing the job. Either way, I replaced the rad cap, and that'll do me until summer of 2019 when I'll get all the belts replaced, flush and change the coolant again, bung on a 76 degree stat and have fitted an aftermarket temp sensor and gauge.

I don't tow, but am fairly modded with heavy wheels and tyres, so want everything running as reliable, cool and untroubled as possible. Will report back, but I'm not expecting anything out of the ordinary now - the testing will be on long mountain climbs.

Owen

 

[Mr III]

I have just replaced my Head on my Surf 97 Gen3, after it has been showing signs of a cracked head for the past 3 years. It finally heated up a little more than normal whilst towing my Westfield 2 months ago.

I bought a Complete Head from Roughtrax along with lots of service items, also bought a 3 core ally rad for a manual with no Trans cooler in it, fitted a separate Mishimoto Trans cooler with an added fan, a new 71c Toyota Thermostat, Water temp gauge and Trans oil temp gauge.

At the same time while doing all the work i blocked off the EGR system and had the Injectors overhauled.
The difference in the drive of the truck is like night and day.

Water temps rarely go over 75c at any time and trans temps on the motorway i usually see around 55c-60c and in town around 75c-85c on hill or little harder use i have seen it climb to 95c, so will have to see what the temps are like when I'm towing my cars around.

Great write up by everyone on here and all the input is so great. have read the whole thread from start to finish.

Thanks
Tony

 

[William Watson]

Why do you keep advertising shoes that is no longer in stock?

 

[William Watson]

Sorry guys wanted to fight a local ad. Did not realize this is not the advertiser's secrion

 

[safari_josh]

Evenin' All.

As many of you will know, I use my 1998 KZJ95 UK-spec Colorado for towing a double horse trailer. When I bought it, I expected the 3.0 litre 1KZ-TE turbo diesel to be well up to the job of pulling around two tons with four or five occupants plus equipment.

The reality has been different and I have suffered constant coolant loss when towing – when the reservoir overflows – and also suffered a cracked cylinder head in 2010. I should say that I don’t hammer the car at all and always try to keep it spinning on as light a throttle as possible when towing.

When I replaced the cylinder head (with a ‘Roughtrax’ unit), I hoped all would be well, but the coolant loss persisted when towing. When running without a trailer it seemed fine, usually.

A couple of weeks back my wife and I were going to collect horse bedding and feed using the empty horse trailer. Travelling along the M9 at normal legal speeds (for trailers) everything was fine and I turned the cabin heater off.
A couple of miles further on I suddenly realised that the temp gauge was ‘off the scale’ so pulled off the motorway and parked-up.

The engine bay was soaked in red coolant and the reservoir was bubbling like a kettle. I turned the motor off and let it cool for 10 mins or so before cautiously removing the radiator cap (heavy gloves and a towel were deployed and a lot more bubbling ensued). I put about 4 litres of red coolant in, started it up and continued, using back roads. All was well (though I did have the cabin heater on this time).

When I eventually got home with the empty trailer, having made the delivery to the Livery Yard, I checked under the bonnet. The top of the radiator was too hot to touch, but the bottom radiator hose was cold.

Two possibilities came to mind:
1. The thermostat I acquired from Milners in 2010 wasn’t working (though I did check it before fitting it).
2. The head gasket was letting combustion pressure into the water channels which was then ejecting the coolant. I discounted a cracked head as there was no sign of steam when re-starting from hot.

So, as the Queen of Hearts would say. . “Off with its head”.

This thread covers my findings when I looked inside and also reports on my investigation into how the 1KZ-TE is designed to be cooled. I have a few misgivings about the design which may shed light on the recurring cracked cylinder head enigma that these motors suffer.

Discussion, as always, will be welcomed.

The cylinder head was removed and cleaned-up. It looked fine and I don’t think there is a problem with it. Its only done about 2,500 miles since it was fitted last June.

View attachment 48850

The first thing I noticed was that one of the ‘blanking panels’ in the head gasket had been inflated. They should all be flat and the old gasket I took out when the head was replaced hadn’t suffered in this way.
This was a pattern ‘three hole’ gasket from Milners – it consists of three thin metal gaskets riveted together. It appears that combustion pressure was getting in between the top and centre sheets as the bottom panel was still flat. This is the front nearside panel, just below the top radiator hose outlet:

View attachment 48851

Other panels in the gasket were normal.

View attachment 48852

Looking closely at the face of the block, the gasket and the cylinder head didn’t show any obvious ‘blow-by’, though I have my suspicions about the rear nearside water channel as the block was a bit discoloured and No. 4 cylinder had a sort of ‘rusty’ look to it (it was like that when the head cracked, but I thought it would have been all shiny again by now).

View attachment 48853

So, maybe I was getting combustion pressure from No. 4 into the coolant and maybe not.

When I fitted the new head I didn’t use any gasket sealant on the head gasket. This time I used a genuine Toyota gasket and put a thin layer of non-setting sealant on both sides of the gasket.
I was very careful not to get any sealant near the camshaft oil feed drillings as I wouldn’t want that blocked.

View attachment 48854

Time will tell if this was a better approach.

So, I may have had a leaky head gasket, I don’t know for sure, but what about the way the motor is designed? Is there anything I can do to improve the cooling when towing??

There are a couple of unusual features with this engine the main one being that this is the only engine I have seen where the thermostat is on the cold water return-side from the radiator. There are undoubtedly others, but I don’t really understand how they are supposed to work.

I’ll explain.

You may be forgiven for thinking that there is a thermostat in here – in the ‘usual place’.

View attachment 48855

But there isn’t, its down here, just behind the alternator.

View attachment 48856

View attachment 48857

As we know, a number of the water channels that connect the head to the block are blanked-off by the head gasket – they can be seen here – four on the nearside & one on the offside:
(Note to all you people who drive on the wrong side of the road . . . British Standard Nearside is the left of the motor, viewed from behind from the driving position).

View attachment 48858

Also, the water pump has no external hoses – it doesn’t take its water directly from the radiator:

View attachment 48859

Instead, the water circulates around the block, past the thermostat – where it is joined by the coolant being returned from the Turbo and the cabin heater and past the large drain hole from the cylinder head.
Then around to the front, where the gallery emerges at the centre of the water pump.
The pump then sends it around to the nearside, below the cylinder head and below the channels blanked-off by the head gasket.

View attachment 48860

Now we see why the water galleries feeding the head are blanked-off, the water (presumably from the coolest part of the engine) now flows between the block and the oil filter housing where it cools (or warms-up) the oil cooler.

View attachment 48861

View attachment 48862

Above the oil cooler are three 5mm holes linking the block and the head, they won’t affect the water circulation much and, I suspect, are primarily there to prevent air locks building up in the block.
On my engine, the holes in the block were a bit rusted-up so I cleaned them out with a 5mm drill bit. The head gasket also had 5mm holes but the head only had 4mm – I drilled these out to 5mm to line everything up and to reduce the risk of blockage. I don’t think the additional 1mm (x 3) will affect the coolant flow.

The coolant now runs to the nearside rear of the block where it meets the first of the galleries connecting the block and the head. As the bulk of the flow continues around the back of the motor it meets more open galleries – allowing water to rise into the head.

At the front off-side of the head is a large drain hole that lets the coolant drop down to the suction side of the water pump. I am assuming at this stage that the thermostat is closed and there is therefore no flow into the radiator, apart from some thermo-syphon exchange that causes the top of the radiator to get hot.
It seems a bit strange to me to deliver the water from the head – probably the hottest part of the motor – downstream of the thermostat.

I have marked-up a picture of the block to illustrate my perception of the coolant flow:

View attachment 48863

As well as the flow up into the head, there is a flow forward on the off side below the head.

Hot water from the head is also routed to the cabin heater, returning to the block upstream of the thermostat. This flow is presumably cooler than the water in the head, so will keep the thermostat cool. I guess this is to maximise the heat transferred to the cabin.

I’m not sure about the turbo charger. There is one feed from the bottom of the block (coolest water) and another just forward of the thermostat. I’m assuming that it’s a thermo-syphon system with the heated water rising up to the upper hose, unless someone can tell me that there’s an impeller in there between the hot and cold sides of the turbo.

So far so good. With the thermostat closed we have a water circulation around the block and the head, with the hottest part being up top, in the alloy head.

And this is where I have a problem . . . .

Normal thermostats that live near the top radiator hose typically open at around 88 degrees Centigrade. One would expect that one living on the return side would have a lower opening temperature – and it does, the standard ‘stat for this motor opens at 82 deg C:

View attachment 48864

However, I carried out an experiment.

I heated the standard stat up in a pan of water and it gradually opened. I ran the hot tap in the kitchen until I couldn’t put my hand in it, then transferred the open stat to the hot tap water – It shut fast in under 3 seconds.
I then put the stat back into the almost boiling pan and it took a long time to open. I repeated the swap and it shut very quickly.

Now, the ‘stat lives in the block with the business end on the inside of the motor. As the motor heats up it will presumably get to the point where it opens and is immediately flooded with cold water from the bottom of the radiator. It seems it will then close very quickly.

Repeat the process – long(ish) time to open followed by a quick shut-off.

I think its very unlikely that the bottom of the radiator will ever get to the temperature where the thermostat stays open (unless you’re stuck in traffic in the Sahara), meaning that the motor is being fed small gulps of cool water.
That is probably OK if the car is running light – but towing a couple of horses over the Pentland Hills??? No wonder the motor gets hot and objects. Its working hard but there is sufficient airflow to keep the radiator cool, so the thermostat stays predominantly shut.
I can see why the motor may get so hot in places that the head is strained – and cracks.
Or does the ‘stat reach a steady state where it balances the heat in the block with the cool water from the radiator ? I don’t know, but I’ll bet it doesn’t open fully very often.

This is not a problem where the ‘stat is at the top of the motor as, when it opens, it is bathed in hot water and so stays open until the whole motor cools down to below its opening temp.

I looked on various websites and all quote the standard ‘stat for this motor as being 82 deg. However, Land Rover Defenders have 88 deg stats, with 74 deg versions as an option.
The Max Ellery manual for the 1KZ-TE states that the standard ‘stat is 74 degrees!
I enquired of Toyota and a 76 deg ‘stat is available – so I’ve fitted one:

View attachment 48865

Whether this will make a difference remains to be seen but my gut feeling is that it won’t. I took the truck for a run (without a trailer) and when I got home the top of the radiator was hot, but the bottom hose was stone cold.
I know that to achieve thermal efficiency the combustion chamber has to be as hot as possible, but unless I’m missing something obvious this design is flawed. My temperature gauge doesn’t normally move from the normal mark – even when its chucking the coolant out. It only reads high when its lost most of the coolant from the head and top of the block and by then it could be too late.

Oh yes, the radiator and cap were new last June. I flushed it out with a hose and it is clean inside.

So, the next step if I still lose coolant when towing ?? – modify the top coolant outlet to take a thermostat and remove the lower one (not that simple as there has to be a steel ring with a rubber gasket around it to make the thermostat cover seal. I’ll just cut the centre out of an old ‘stat and put the outer part back in).
There isn’t a great deal of space for a conventional thermostat where the coolant exits the head so I might have to be innovative with some alloy welding. I used to have a BMW K1200 motorcycle that had a cylindrical thermostat that passed enough fluid to cool a 130 BHP motor with two small radiators (and fry my knees in traffic). Maybe one of those could be adapted to fit.

View attachment 48866

Food for thought.

OK folks, over to you, tell me where my theories are flawed and what I have been doing wrong.

But remember . . . 1,000,000 cracked heads don’t lie .

Bob.

I am just about to buy my first Toyota 90 series either from the uk or southern africa. Just a few days ago I was driving one around Botswana (auto 1- kz te, jap import) and i was seriously impressed. Obviously we weren't towing (this time) but temperatures were high 30's low 40's. Lots of sand and off roading. I kept my eye on the temperature the whole time and it didn't go up. I'm not sure of the year but '97 or '98. I look forward to reading back through your threads Bob and everyone else's. Days of my Land Rover 2.8i are over! ps if anyone has a manual 2002 vx i'd love to hear more about it.

 

[Road runner]

Bob, as you know, I don't have a 90 any more, but I really think that you are onto something there. That is fascinating. My head cracked on the first 95 auto and it's a major flaw in an otherwise really good vehicle. I know you shouldn't run with out a stat really, but if you did a lot of heavy towing it might be better to do with with the unit removed. I wonder how the bottom hose would feel if you ran with no stat. I always took a cold bottom hose to mean effective cooling. Maybe it just means that no hot water is circulating! Considering a separate oil cooler too? A full length manual rad and cooler would give better heat removal.

Chris

EDF

The 6 cylinder 1HD family. I do not think any of the D4Ds have this problem either. Not aware of any material difference in the cooling systems other than the apparently superior design of the head in terms of coolant flow.

I'm not sure that the 1HD's don't have the same set-up The 'stat sits in the engine-side of the bottom hose, but I don't know which way the flow goes...
Are you sure that your description of the flow on the KZ-TE is correct? (I don't know the answer but it would be worth confirming while theorising over the problem and possible solutions)

I bought a surf several years ago from a mechanic who had replaced the surf radiator with a landcruiser radiator also fitted a trans cooler. No problems.

Evenin' All.

As many of you will know, I use my 1998 KZJ95 UK-spec Colorado for towing a double horse trailer. When I bought it, I expected the 3.0 litre 1KZ-TE turbo diesel to be well up to the job of pulling around two tons with four or five occupants plus equipment.

The reality has been different and I have suffered constant coolant loss when towing – when the reservoir overflows – and also suffered a cracked cylinder head in 2010. I should say that I don’t hammer the car at all and always try to keep it spinning on as light a throttle as possible when towing.

When I replaced the cylinder head (with a ‘Roughtrax’ unit), I hoped all would be well, but the coolant loss persisted when towing. When running without a trailer it seemed fine, usually.

A couple of weeks back my wife and I were going to collect horse bedding and feed using the empty horse trailer. Travelling along the M9 at normal legal speeds (for trailers) everything was fine and I turned the cabin heater off.
A couple of miles further on I suddenly realised that the temp gauge was ‘off the scale’ so pulled off the motorway and parked-up.

The engine bay was soaked in red coolant and the reservoir was bubbling like a kettle. I turned the motor off and let it cool for 10 mins or so before cautiously removing the radiator cap (heavy gloves and a towel were deployed and a lot more bubbling ensued). I put about 4 litres of red coolant in, started it up and continued, using back roads. All was well (though I did have the cabin heater on this time).

When I eventually got home with the empty trailer, having made the delivery to the Livery Yard, I checked under the bonnet. The top of the radiator was too hot to touch, but the bottom radiator hose was cold.

Two possibilities came to mind:
1. The thermostat I acquired from Milners in 2010 wasn’t working (though I did check it before fitting it).
2. The head gasket was letting combustion pressure into the water channels which was then ejecting the coolant. I discounted a cracked head as there was no sign of steam when re-starting from hot.

So, as the Queen of Hearts would say. . “Off with its head”.

This thread covers my findings when I looked inside and also reports on my investigation into how the 1KZ-TE is designed to be cooled. I have a few misgivings about the design which may shed light on the recurring cracked cylinder head enigma that these motors suffer.

Discussion, as always, will be welcomed.

The cylinder head was removed and cleaned-up. It looked fine and I don’t think there is a problem with it. Its only done about 2,500 miles since it was fitted last June.

View attachment 48850

The first thing I noticed was that one of the ‘blanking panels’ in the head gasket had been inflated. They should all be flat and the old gasket I took out when the head was replaced hadn’t suffered in this way.
This was a pattern ‘three hole’ gasket from Milners – it consists of three thin metal gaskets riveted together. It appears that combustion pressure was getting in between the top and centre sheets as the bottom panel was still flat. This is the front nearside panel, just below the top radiator hose outlet:

View attachment 48851

Other panels in the gasket were normal.

View attachment 48852

Looking closely at the face of the block, the gasket and the cylinder head didn’t show any obvious ‘blow-by’, though I have my suspicions about the rear nearside water channel as the block was a bit discoloured and No. 4 cylinder had a sort of ‘rusty’ look to it (it was like that when the head cracked, but I thought it would have been all shiny again by now).

View attachment 48853

So, maybe I was getting combustion pressure from No. 4 into the coolant and maybe not.

When I fitted the new head I didn’t use any gasket sealant on the head gasket. This time I used a genuine Toyota gasket and put a thin layer of non-setting sealant on both sides of the gasket.
I was very careful not to get any sealant near the camshaft oil feed drillings as I wouldn’t want that blocked.

View attachment 48854

Time will tell if this was a better approach.

So, I may have had a leaky head gasket, I don’t know for sure, but what about the way the motor is designed? Is there anything I can do to improve the cooling when towing??

There are a couple of unusual features with this engine the main one being that this is the only engine I have seen where the thermostat is on the cold water return-side from the radiator. There are undoubtedly others, but I don’t really understand how they are supposed to work.

I’ll explain.

You may be forgiven for thinking that there is a thermostat in here – in the ‘usual place’.

View attachment 48855

But there isn’t, its down here, just behind the alternator.

View attachment 48856

View attachment 48857

As we know, a number of the water channels that connect the head to the block are blanked-off by the head gasket – they can be seen here – four on the nearside & one on the offside:
(Note to all you people who drive on the wrong side of the road . . . British Standard Nearside is the left of the motor, viewed from behind from the driving position).

View attachment 48858

Also, the water pump has no external hoses – it doesn’t take its water directly from the radiator:

View attachment 48859

Instead, the water circulates around the block, past the thermostat – where it is joined by the coolant being returned from the Turbo and the cabin heater and past the large drain hole from the cylinder head.
Then around to the front, where the gallery emerges at the centre of the water pump.
The pump then sends it around to the nearside, below the cylinder head and below the channels blanked-off by the head gasket.

View attachment 48860

Now we see why the water galleries feeding the head are blanked-off, the water (presumably from the coolest part of the engine) now flows between the block and the oil filter housing where it cools (or warms-up) the oil cooler.

View attachment 48861

View attachment 48862

Above the oil cooler are three 5mm holes linking the block and the head, they won’t affect the water circulation much and, I suspect, are primarily there to prevent air locks building up in the block.
On my engine, the holes in the block were a bit rusted-up so I cleaned them out with a 5mm drill bit. The head gasket also had 5mm holes but the head only had 4mm – I drilled these out to 5mm to line everything up and to reduce the risk of blockage. I don’t think the additional 1mm (x 3) will affect the coolant flow.

The coolant now runs to the nearside rear of the block where it meets the first of the galleries connecting the block and the head. As the bulk of the flow continues around the back of the motor it meets more open galleries – allowing water to rise into the head.

At the front off-side of the head is a large drain hole that lets the coolant drop down to the suction side of the water pump. I am assuming at this stage that the thermostat is closed and there is therefore no flow into the radiator, apart from some thermo-syphon exchange that causes the top of the radiator to get hot.
It seems a bit strange to me to deliver the water from the head – probably the hottest part of the motor – downstream of the thermostat.

I have marked-up a picture of the block to illustrate my perception of the coolant flow:

View attachment 48863

As well as the flow up into the head, there is a flow forward on the off side below the head.

Hot water from the head is also routed to the cabin heater, returning to the block upstream of the thermostat. This flow is presumably cooler than the water in the head, so will keep the thermostat cool. I guess this is to maximise the heat transferred to the cabin.

I’m not sure about the turbo charger. There is one feed from the bottom of the block (coolest water) and another just forward of the thermostat. I’m assuming that it’s a thermo-syphon system with the heated water rising up to the upper hose, unless someone can tell me that there’s an impeller in there between the hot and cold sides of the turbo.

So far so good. With the thermostat closed we have a water circulation around the block and the head, with the hottest part being up top, in the alloy head.

And this is where I have a problem . . . .

Normal thermostats that live near the top radiator hose typically open at around 88 degrees Centigrade. One would expect that one living on the return side would have a lower opening temperature – and it does, the standard ‘stat for this motor opens at 82 deg C:

View attachment 48864

However, I carried out an experiment.

I heated the standard stat up in a pan of water and it gradually opened. I ran the hot tap in the kitchen until I couldn’t put my hand in it, then transferred the open stat to the hot tap water – It shut fast in under 3 seconds.
I then put the stat back into the almost boiling pan and it took a long time to open. I repeated the swap and it shut very quickly.

Now, the ‘stat lives in the block with the business end on the inside of the motor. As the motor heats up it will presumably get to the point where it opens and is immediately flooded with cold water from the bottom of the radiator. It seems it will then close very quickly.

Repeat the process – long(ish) time to open followed by a quick shut-off.

I think its very unlikely that the bottom of the radiator will ever get to the temperature where the thermostat stays open (unless you’re stuck in traffic in the Sahara), meaning that the motor is being fed small gulps of cool water.
That is probably OK if the car is running light – but towing a couple of horses over the Pentland Hills??? No wonder the motor gets hot and objects. Its working hard but there is sufficient airflow to keep the radiator cool, so the thermostat stays predominantly shut.
I can see why the motor may get so hot in places that the head is strained – and cracks.
Or does the ‘stat reach a steady state where it balances the heat in the block with the cool water from the radiator ? I don’t know, but I’ll bet it doesn’t open fully very often.

This is not a problem where the ‘stat is at the top of the motor as, when it opens, it is bathed in hot water and so stays open until the whole motor cools down to below its opening temp.

I looked on various websites and all quote the standard ‘stat for this motor as being 82 deg. However, Land Rover Defenders have 88 deg stats, with 74 deg versions as an option.
The Max Ellery manual for the 1KZ-TE states that the standard ‘stat is 74 degrees!
I enquired of Toyota and a 76 deg ‘stat is available – so I’ve fitted one:

View attachment 48865

Whether this will make a difference remains to be seen but my gut feeling is that it won’t. I took the truck for a run (without a trailer) and when I got home the top of the radiator was hot, but the bottom hose was stone cold.
I know that to achieve thermal efficiency the combustion chamber has to be as hot as possible, but unless I’m missing something obvious this design is flawed. My temperature gauge doesn’t normally move from the normal mark – even when its chucking the coolant out. It only reads high when its lost most of the coolant from the head and top of the block and by then it could be too late.

Oh yes, the radiator and cap were new last June. I flushed it out with a hose and it is clean inside.

So, the next step if I still lose coolant when towing ?? – modify the top coolant outlet to take a thermostat and remove the lower one (not that simple as there has to be a steel ring with a rubber gasket around it to make the thermostat cover seal. I’ll just cut the centre out of an old ‘stat and put the outer part back in).
There isn’t a great deal of space for a conventional thermostat where the coolant exits the head so I might have to be innovative with some alloy welding. I used to have a BMW K1200 motorcycle that had a cylindrical thermostat that passed enough fluid to cool a 130 BHP motor with two small radiators (and fry my knees in traffic). Maybe one of those could be adapted to fit.

View attachment 48866

Food for thought.

OK folks, over to you, tell me where my theories are flawed and what I have been doing wrong.

But remember . . . 1,000,000 cracked heads don’t lie .

Bob.

 

[Road runner]

I bought a surf several years ago who had fitted a landcruiser radiator and after market trans cooler and it was his general work and tow wagon. I never had any problems. The other comment is use genuine Toyota parts

 

[Adam]

Evenin' All.

As many of you will know, I use my 1998 KZJ95 UK-spec Colorado for towing a double horse trailer. When I bought it, I expected the 3.0 litre 1KZ-TE turbo diesel to be well up to the job of pulling around two tons with four or five occupants plus equipment.

The reality has been different and I have suffered constant coolant loss when towing – when the reservoir overflows – and also suffered a cracked cylinder head in 2010. I should say that I don’t hammer the car at all and always try to keep it spinning on as light a throttle as possible when towing.

When I replaced the cylinder head (with a ‘Roughtrax’ unit), I hoped all would be well, but the coolant loss persisted when towing. When running without a trailer it seemed fine, usually.

A couple of weeks back my wife and I were going to collect horse bedding and feed using the empty horse trailer. Travelling along the M9 at normal legal speeds (for trailers) everything was fine and I turned the cabin heater off.
A couple of miles further on I suddenly realised that the temp gauge was ‘off the scale’ so pulled off the motorway and parked-up.

The engine bay was soaked in red coolant and the reservoir was bubbling like a kettle. I turned the motor off and let it cool for 10 mins or so before cautiously removing the radiator cap (heavy gloves and a towel were deployed and a lot more bubbling ensued). I put about 4 litres of red coolant in, started it up and continued, using back roads. All was well (though I did have the cabin heater on this time).

When I eventually got home with the empty trailer, having made the delivery to the Livery Yard, I checked under the bonnet. The top of the radiator was too hot to touch, but the bottom radiator hose was cold.

Two possibilities came to mind:
1. The thermostat I acquired from Milners in 2010 wasn’t working (though I did check it before fitting it).
2. The head gasket was letting combustion pressure into the water channels which was then ejecting the coolant. I discounted a cracked head as there was no sign of steam when re-starting from hot.

So, as the Queen of Hearts would say. . “Off with its head”.

This thread covers my findings when I looked inside and also reports on my investigation into how the 1KZ-TE is designed to be cooled. I have a few misgivings about the design which may shed light on the recurring cracked cylinder head enigma that these motors suffer.

Discussion, as always, will be welcomed.

The cylinder head was removed and cleaned-up. It looked fine and I don’t think there is a problem with it. Its only done about 2,500 miles since it was fitted last June.

View attachment 48850

The first thing I noticed was that one of the ‘blanking panels’ in the head gasket had been inflated. They should all be flat and the old gasket I took out when the head was replaced hadn’t suffered in this way.
This was a pattern ‘three hole’ gasket from Milners – it consists of three thin metal gaskets riveted together. It appears that combustion pressure was getting in between the top and centre sheets as the bottom panel was still flat. This is the front nearside panel, just below the top radiator hose outlet:

View attachment 48851

Other panels in the gasket were normal.

View attachment 48852

Looking closely at the face of the block, the gasket and the cylinder head didn’t show any obvious ‘blow-by’, though I have my suspicions about the rear nearside water channel as the block was a bit discoloured and No. 4 cylinder had a sort of ‘rusty’ look to it (it was like that when the head cracked, but I thought it would have been all shiny again by now).

View attachment 48853

So, maybe I was getting combustion pressure from No. 4 into the coolant and maybe not.

When I fitted the new head I didn’t use any gasket sealant on the head gasket. This time I used a genuine Toyota gasket and put a thin layer of non-setting sealant on both sides of the gasket.
I was very careful not to get any sealant near the camshaft oil feed drillings as I wouldn’t want that blocked.

View attachment 48854

Time will tell if this was a better approach.

So, I may have had a leaky head gasket, I don’t know for sure, but what about the way the motor is designed? Is there anything I can do to improve the cooling when towing??

There are a couple of unusual features with this engine the main one being that this is the only engine I have seen where the thermostat is on the cold water return-side from the radiator. There are undoubtedly others, but I don’t really understand how they are supposed to work.

I’ll explain.

You may be forgiven for thinking that there is a thermostat in here – in the ‘usual place’.

View attachment 48855

But there isn’t, its down here, just behind the alternator.

View attachment 48856

View attachment 48857

As we know, a number of the water channels that connect the head to the block are blanked-off by the head gasket – they can be seen here – four on the nearside & one on the offside:
(Note to all you people who drive on the wrong side of the road . . . British Standard Nearside is the left of the motor, viewed from behind from the driving position).

View attachment 48858

Also, the water pump has no external hoses – it doesn’t take its water directly from the radiator:

View attachment 48859

Instead, the water circulates around the block, past the thermostat – where it is joined by the coolant being returned from the Turbo and the cabin heater and past the large drain hole from the cylinder head.
Then around to the front, where the gallery emerges at the centre of the water pump.
The pump then sends it around to the nearside, below the cylinder head and below the channels blanked-off by the head gasket.

View attachment 48860

Now we see why the water galleries feeding the head are blanked-off, the water (presumably from the coolest part of the engine) now flows between the block and the oil filter housing where it cools (or warms-up) the oil cooler.

View attachment 48861

View attachment 48862

Above the oil cooler are three 5mm holes linking the block and the head, they won’t affect the water circulation much and, I suspect, are primarily there to prevent air locks building up in the block.
On my engine, the holes in the block were a bit rusted-up so I cleaned them out with a 5mm drill bit. The head gasket also had 5mm holes but the head only had 4mm – I drilled these out to 5mm to line everything up and to reduce the risk of blockage. I don’t think the additional 1mm (x 3) will affect the coolant flow.

The coolant now runs to the nearside rear of the block where it meets the first of the galleries connecting the block and the head. As the bulk of the flow continues around the back of the motor it meets more open galleries – allowing water to rise into the head.

At the front off-side of the head is a large drain hole that lets the coolant drop down to the suction side of the water pump. I am assuming at this stage that the thermostat is closed and there is therefore no flow into the radiator, apart from some thermo-syphon exchange that causes the top of the radiator to get hot.
It seems a bit strange to me to deliver the water from the head – probably the hottest part of the motor – downstream of the thermostat.

I have marked-up a picture of the block to illustrate my perception of the coolant flow:

View attachment 48863

As well as the flow up into the head, there is a flow forward on the off side below the head.

Hot water from the head is also routed to the cabin heater, returning to the block upstream of the thermostat. This flow is presumably cooler than the water in the head, so will keep the thermostat cool. I guess this is to maximise the heat transferred to the cabin.

I’m not sure about the turbo charger. There is one feed from the bottom of the block (coolest water) and another just forward of the thermostat. I’m assuming that it’s a thermo-syphon system with the heated water rising up to the upper hose, unless someone can tell me that there’s an impeller in there between the hot and cold sides of the turbo.

So far so good. With the thermostat closed we have a water circulation around the block and the head, with the hottest part being up top, in the alloy head.

And this is where I have a problem . . . .

Normal thermostats that live near the top radiator hose typically open at around 88 degrees Centigrade. One would expect that one living on the return side would have a lower opening temperature – and it does, the standard ‘stat for this motor opens at 82 deg C:

View attachment 48864

However, I carried out an experiment.

I heated the standard stat up in a pan of water and it gradually opened. I ran the hot tap in the kitchen until I couldn’t put my hand in it, then transferred the open stat to the hot tap water – It shut fast in under 3 seconds.
I then put the stat back into the almost boiling pan and it took a long time to open. I repeated the swap and it shut very quickly.

Now, the ‘stat lives in the block with the business end on the inside of the motor. As the motor heats up it will presumably get to the point where it opens and is immediately flooded with cold water from the bottom of the radiator. It seems it will then close very quickly.

Repeat the process – long(ish) time to open followed by a quick shut-off.

I think its very unlikely that the bottom of the radiator will ever get to the temperature where the thermostat stays open (unless you’re stuck in traffic in the Sahara), meaning that the motor is being fed small gulps of cool water.
That is probably OK if the car is running light – but towing a couple of horses over the Pentland Hills??? No wonder the motor gets hot and objects. Its working hard but there is sufficient airflow to keep the radiator cool, so the thermostat stays predominantly shut.
I can see why the motor may get so hot in places that the head is strained – and cracks.
Or does the ‘stat reach a steady state where it balances the heat in the block with the cool water from the radiator ? I don’t know, but I’ll bet it doesn’t open fully very often.

This is not a problem where the ‘stat is at the top of the motor as, when it opens, it is bathed in hot water and so stays open until the whole motor cools down to below its opening temp.

I looked on various websites and all quote the standard ‘stat for this motor as being 82 deg. However, Land Rover Defenders have 88 deg stats, with 74 deg versions as an option.
The Max Ellery manual for the 1KZ-TE states that the standard ‘stat is 74 degrees!
I enquired of Toyota and a 76 deg ‘stat is available – so I’ve fitted one:

View attachment 48865

Whether this will make a difference remains to be seen but my gut feeling is that it won’t. I took the truck for a run (without a trailer) and when I got home the top of the radiator was hot, but the bottom hose was stone cold.
I know that to achieve thermal efficiency the combustion chamber has to be as hot as possible, but unless I’m missing something obvious this design is flawed. My temperature gauge doesn’t normally move from the normal mark – even when its chucking the coolant out. It only reads high when its lost most of the coolant from the head and top of the block and by then it could be too late.

Oh yes, the radiator and cap were new last June. I flushed it out with a hose and it is clean inside.

So, the next step if I still lose coolant when towing ?? – modify the top coolant outlet to take a thermostat and remove the lower one (not that simple as there has to be a steel ring with a rubber gasket around it to make the thermostat cover seal. I’ll just cut the centre out of an old ‘stat and put the outer part back in).
There isn’t a great deal of space for a conventional thermostat where the coolant exits the head so I might have to be innovative with some alloy welding. I used to have a BMW K1200 motorcycle that had a cylindrical thermostat that passed enough fluid to cool a 130 BHP motor with two small radiators (and fry my knees in traffic). Maybe one of those could be adapted to fit.

View attachment 48866

Food for thought.

OK folks, over to you, tell me where my theories are flawed and what I have been doing wrong.

But remember . . . 1,000,000 cracked heads don’t lie .

Bob.

Evenin' All.

As many of you will know, I use my 1998 KZJ95 UK-spec Colorado for towing a double horse trailer. When I bought it, I expected the 3.0 litre 1KZ-TE turbo diesel to be well up to the job of pulling around two tons with four or five occupants plus equipment.

The reality has been different and I have suffered constant coolant loss when towing – when the reservoir overflows – and also suffered a cracked cylinder head in 2010. I should say that I don’t hammer the car at all and always try to keep it spinning on as light a throttle as possible when towing.

When I replaced the cylinder head (with a ‘Roughtrax’ unit), I hoped all would be well, but the coolant loss persisted when towing. When running without a trailer it seemed fine, usually.

A couple of weeks back my wife and I were going to collect horse bedding and feed using the empty horse trailer. Travelling along the M9 at normal legal speeds (for trailers) everything was fine and I turned the cabin heater off.
A couple of miles further on I suddenly realised that the temp gauge was ‘off the scale’ so pulled off the motorway and parked-up.

The engine bay was soaked in red coolant and the reservoir was bubbling like a kettle. I turned the motor off and let it cool for 10 mins or so before cautiously removing the radiator cap (heavy gloves and a towel were deployed and a lot more bubbling ensued). I put about 4 litres of red coolant in, started it up and continued, using back roads. All was well (though I did have the cabin heater on this time).

When I eventually got home with the empty trailer, having made the delivery to the Livery Yard, I checked under the bonnet. The top of the radiator was too hot to touch, but the bottom radiator hose was cold.

Two possibilities came to mind:
1. The thermostat I acquired from Milners in 2010 wasn’t working (though I did check it before fitting it).
2. The head gasket was letting combustion pressure into the water channels which was then ejecting the coolant. I discounted a cracked head as there was no sign of steam when re-starting from hot.

So, as the Queen of Hearts would say. . “Off with its head”.

This thread covers my findings when I looked inside and also reports on my investigation into how the 1KZ-TE is designed to be cooled. I have a few misgivings about the design which may shed light on the recurring cracked cylinder head enigma that these motors suffer.

Discussion, as always, will be welcomed.

The cylinder head was removed and cleaned-up. It looked fine and I don’t think there is a problem with it. Its only done about 2,500 miles since it was fitted last June.

View attachment 48850

The first thing I noticed was that one of the ‘blanking panels’ in the head gasket had been inflated. They should all be flat and the old gasket I took out when the head was replaced hadn’t suffered in this way.
This was a pattern ‘three hole’ gasket from Milners – it consists of three thin metal gaskets riveted together. It appears that combustion pressure was getting in between the top and centre sheets as the bottom panel was still flat. This is the front nearside panel, just below the top radiator hose outlet:

View attachment 48851

Other panels in the gasket were normal.

View attachment 48852

Looking closely at the face of the block, the gasket and the cylinder head didn’t show any obvious ‘blow-by’, though I have my suspicions about the rear nearside water channel as the block was a bit discoloured and No. 4 cylinder had a sort of ‘rusty’ look to it (it was like that when the head cracked, but I thought it would have been all shiny again by now).

View attachment 48853

So, maybe I was getting combustion pressure from No. 4 into the coolant and maybe not.

When I fitted the new head I didn’t use any gasket sealant on the head gasket. This time I used a genuine Toyota gasket and put a thin layer of non-setting sealant on both sides of the gasket.
I was very careful not to get any sealant near the camshaft oil feed drillings as I wouldn’t want that blocked.

View attachment 48854

Time will tell if this was a better approach.

So, I may have had a leaky head gasket, I don’t know for sure, but what about the way the motor is designed? Is there anything I can do to improve the cooling when towing??

There are a couple of unusual features with this engine the main one being that this is the only engine I have seen where the thermostat is on the cold water return-side from the radiator. There are undoubtedly others, but I don’t really understand how they are supposed to work.

I’ll explain.

You may be forgiven for thinking that there is a thermostat in here – in the ‘usual place’.

View attachment 48855

But there isn’t, its down here, just behind the alternator.

View attachment 48856

View attachment 48857

As we know, a number of the water channels that connect the head to the block are blanked-off by the head gasket – they can be seen here – four on the nearside & one on the offside:
(Note to all you people who drive on the wrong side of the road . . . British Standard Nearside is the left of the motor, viewed from behind from the driving position).

View attachment 48858

Also, the water pump has no external hoses – it doesn’t take its water directly from the radiator:

View attachment 48859

Instead, the water circulates around the block, past the thermostat – where it is joined by the coolant being returned from the Turbo and the cabin heater and past the large drain hole from the cylinder head.
Then around to the front, where the gallery emerges at the centre of the water pump.
The pump then sends it around to the nearside, below the cylinder head and below the channels blanked-off by the head gasket.

View attachment 48860

Now we see why the water galleries feeding the head are blanked-off, the water (presumably from the coolest part of the engine) now flows between the block and the oil filter housing where it cools (or warms-up) the oil cooler.

View attachment 48861

View attachment 48862

Above the oil cooler are three 5mm holes linking the block and the head, they won’t affect the water circulation much and, I suspect, are primarily there to prevent air locks building up in the block.
On my engine, the holes in the block were a bit rusted-up so I cleaned them out with a 5mm drill bit. The head gasket also had 5mm holes but the head only had 4mm – I drilled these out to 5mm to line everything up and to reduce the risk of blockage. I don’t think the additional 1mm (x 3) will affect the coolant flow.

The coolant now runs to the nearside rear of the block where it meets the first of the galleries connecting the block and the head. As the bulk of the flow continues around the back of the motor it meets more open galleries – allowing water to rise into the head.

At the front off-side of the head is a large drain hole that lets the coolant drop down to the suction side of the water pump. I am assuming at this stage that the thermostat is closed and there is therefore no flow into the radiator, apart from some thermo-syphon exchange that causes the top of the radiator to get hot.
It seems a bit strange to me to deliver the water from the head – probably the hottest part of the motor – downstream of the thermostat.

I have marked-up a picture of the block to illustrate my perception of the coolant flow:

View attachment 48863

As well as the flow up into the head, there is a flow forward on the off side below the head.

Hot water from the head is also routed to the cabin heater, returning to the block upstream of the thermostat. This flow is presumably cooler than the water in the head, so will keep the thermostat cool. I guess this is to maximise the heat transferred to the cabin.

I’m not sure about the turbo charger. There is one feed from the bottom of the block (coolest water) and another just forward of the thermostat. I’m assuming that it’s a thermo-syphon system with the heated water rising up to the upper hose, unless someone can tell me that there’s an impeller in there between the hot and cold sides of the turbo.

So far so good. With the thermostat closed we have a water circulation around the block and the head, with the hottest part being up top, in the alloy head.

And this is where I have a problem . . . .

Normal thermostats that live near the top radiator hose typically open at around 88 degrees Centigrade. One would expect that one living on the return side would have a lower opening temperature – and it does, the standard ‘stat for this motor opens at 82 deg C:

View attachment 48864

However, I carried out an experiment.

I heated the standard stat up in a pan of water and it gradually opened. I ran the hot tap in the kitchen until I couldn’t put my hand in it, then transferred the open stat to the hot tap water – It shut fast in under 3 seconds.
I then put the stat back into the almost boiling pan and it took a long time to open. I repeated the swap and it shut very quickly.

Now, the ‘stat lives in the block with the business end on the inside of the motor. As the motor heats up it will presumably get to the point where it opens and is immediately flooded with cold water from the bottom of the radiator. It seems it will then close very quickly.

Repeat the process – long(ish) time to open followed by a quick shut-off.

I think its very unlikely that the bottom of the radiator will ever get to the temperature where the thermostat stays open (unless you’re stuck in traffic in the Sahara), meaning that the motor is being fed small gulps of cool water.
That is probably OK if the car is running light – but towing a couple of horses over the Pentland Hills??? No wonder the motor gets hot and objects. Its working hard but there is sufficient airflow to keep the radiator cool, so the thermostat stays predominantly shut.
I can see why the motor may get so hot in places that the head is strained – and cracks.
Or does the ‘stat reach a steady state where it balances the heat in the block with the cool water from the radiator ? I don’t know, but I’ll bet it doesn’t open fully very often.

This is not a problem where the ‘stat is at the top of the motor as, when it opens, it is bathed in hot water and so stays open until the whole motor cools down to below its opening temp.

I looked on various websites and all quote the standard ‘stat for this motor as being 82 deg. However, Land Rover Defenders have 88 deg stats, with 74 deg versions as an option.
The Max Ellery manual for the 1KZ-TE states that the standard ‘stat is 74 degrees!
I enquired of Toyota and a 76 deg ‘stat is available – so I’ve fitted one:

View attachment 48865

Whether this will make a difference remains to be seen but my gut feeling is that it won’t. I took the truck for a run (without a trailer) and when I got home the top of the radiator was hot, but the bottom hose was stone cold.
I know that to achieve thermal efficiency the combustion chamber has to be as hot as possible, but unless I’m missing something obvious this design is flawed. My temperature gauge doesn’t normally move from the normal mark – even when its chucking the coolant out. It only reads high when its lost most of the coolant from the head and top of the block and by then it could be too late.

Oh yes, the radiator and cap were new last June. I flushed it out with a hose and it is clean inside.

So, the next step if I still lose coolant when towing ?? – modify the top coolant outlet to take a thermostat and remove the lower one (not that simple as there has to be a steel ring with a rubber gasket around it to make the thermostat cover seal. I’ll just cut the centre out of an old ‘stat and put the outer part back in).
There isn’t a great deal of space for a conventional thermostat where the coolant exits the head so I might have to be innovative with some alloy welding. I used to have a BMW K1200 motorcycle that had a cylindrical thermostat that passed enough fluid to cool a 130 BHP motor with two small radiators (and fry my knees in traffic). Maybe one of those could be adapted to fit.

View attachment 48866

Food for thought.

OK folks, over to you, tell me where my theories are flawed and what I have been doing wrong.

But remember . . . 1,000,000 cracked heads don’t lie .

Bob.

i have a 3.0td land cruiser done 210k and drive it hard most of the time. Also made it pull over well over 3 ton the odd time to and never had a heat problem. Maybe a blocked rad or something could of been at fault to start with. But I’d say the head or any engine parts you had was rough trax are poor and not up to the job. A lot of them places like that just sell cheap shit I’d not even have a oil filte or anything from any of them. Iv seen radiators That hold less water volume off such places too

 

[Tommogen3]

Hello guys, just read through every post. but my overheating problem is different.
bit of background.
Its a 96 Gen 3 surf.
I have installed a stainless 3" downpipe and exhaust myself.
I also installed a charge cooler which I made myself.
its electronically boosted to 1.1 bar
fuel screw has been given 2 turns to the right on the spill control valve.
RUNS GREAT.

Until, 2 days ago when i noticed all the rusty coolant running out the side of the engine.. it was a hot day and i had the aircon on..

I get home and find that its leaking from where the thermostat is bolted on.
I remove the pipe over the thermostat, and replace the thermostat with a new 82* degrees one.
I drive 6 miles and coolant is leaking out again. temps were rising.

Something is causing too much pressure in the water system and its blowing the thermostat seal before it opens.
Now, before i go onto a full coolant flush, new radiator, new 72* thermostat etc...

Is this a sign the head gasket is gone, or the head is cracked?
This is a expense i can do without with right now. based in somerset. cheers. Tom.

 

[StarCruiser]

A good test is from cold, remove rad cap and start engine. Check for bubbles and block off the filler with your hand as well as any overflow. See if any pressure builds fairly quickly. If not then your head gasket could be ok.

 

[Tommogen3]

Ok, I started it and let it run. I had the radiator cap off and had my hand over it. I could not feel any pressure building up. and i didn't see any bubbles. earlier on, when it was hotter and i was filling it up. it did bubble up a bit. and also it was coming out on up idle but i think that's normal.

 

[Beau]

Sounds like a problem directly related to where the thermostat bolts on. More common to blow a hose if the system has pressure in it. I would check back that area