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The dreaded top tube leak - 5VZFE

Damien

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Nov 21, 2017
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australia
Hi guys I am looking for some ideas/wisdom.

Awhile ago I rebuilt my 5VZFE. Did the heads. Rear seals all of it. Goes great. Did the knock sensors. But it did seem to eat more coolant than is normal. Went in to it today. Turns out I missed the deal with the darn rusting top tube.

I should have known since it has little white paint dots all over it for places that have now become leaks!

What I think has happened is that where the coolant bypass joins at the rear exit end of the tube where it goes upwards after it exits the block it has begun to leak. That has flowed down back along the tube and pooled up between the heads at the back. I am pretty sure this is not a leak from the manifold above or a leak from the gaskets or the welch plugs.

Anyway I've got a replacement ( used ) tube to put in.

But before I go ahead and just repeat the same problem I am wondering if anyone has ever deleted/bypassed this darn tubing nightmare since I am pretty sure it is going to be a problem again.

Has anyone ever done something like :

1. Cut the little rust nipple off the bypass tube and then covered that area with tubing to seal it up. Then close up the circuit where it goes to the EFI ( loop it to itself ). I am not planning on going to the snow and not worried about it freezing and I am not considering this a performance modification. More a remove the problem modification.

2. Going one step further delete the entire evil tube from between the heads cap off the port from the block. Then lead a coolant to the circuit at the back from somewhere else hot. T barb. You get the general drift. Put it somewhere else that is not between the heads.

If option 2 isn't entirely insane where might be a good place to put a T-barb in and lead a tube from ?

Am I insane and is this a crazy idea anyone done this ?

I also posted this over at the PradoPoint forum to see if anyone thar might have any ideas.

Thanks !
 
Some photos might help for those of us not familiar with this tube and the engine you have, like me...
 
I was thinking the same Clive!

I was also thinking, can a new tube be made up from 316 Stainless steel without too much ado? Without seeing it, I wouldn't know how difficult that may be.
 
Hey guys! Will have pictures tomorrow but in the meantime I found a nice parts diagram on the megazip that makes it even clearer.

https://www.megazip.net/zapchasti-d...l-gkpekl-596772/radiator-water-outlet-7454564

The fail engineering is part 16268.

The "coolant leak generator" :)

It seems that the idea is to hide a critical coolant tube made of poor quality metals deep in the engine between the heads where it can leak unseen. It has a secondary purpose of flowing coolant through the EFI ( throttle body really ) So that it can make the top of the EFI ( top manifold stuff ) ridiculously hot so you can cook eggs on it.

It seems that most often it is that little 90 degree barb at the back that goes on up to the throttle body where it rusts out. The barb for that tube is welded on and either some differing metal type chemistry or they are just poor welds.

I've got pictures of where it has leaked that I will post tomorrow. The more I look at it the more I am tempted to delete it :|
 
Did a quick sketch of what I was thinking.
Untitled Diagram.jpg
 
Think I might be inclined to shorten it and replace it with some silicone hose or sleeve the whole thing or even copy it in soft copper fridge pipe.

Do you use the genuine Toyota red coolant?
 
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Yup always use the red stuff. Not sure if previous owners did. While we have had it has never seen the temp climb past half way. Though the temp gauge only seems to have two states. Cold and half way!

Thankfully previous owners didn't use green but I think they put tap water in it. This time around it is getting a new radiator and previously when I did the heads I noticed the coolant ports in the block were starting to wear like they had a hard life of salt and some left over gunk which I assume was an effort at stop leak that all had collected up in the block under the gaskets. I tore the whole block down. Cleaned out every single port. Flowed good clean red through it.

I spent a lot of time on the heads and block till it was all smooth and had a mirror finish. Smoothed out the edges of the worn ports. Seems like the work paid off since when I looked down between the heads everything is buttoned up really nicely. Just this stupid tube !

I thought about shortening it and replacing it with a hose as well. That was my first instinct. Get rid of the metal. Get rid of the rust. It would also mean you could just pull the barbed part out of that hose where it comes out of the space between the heads at the other end without having to get in between the heads. But it gets pretty hot under all the stuff that goes on top and Toyota clearly thought this needed something metal to get the job done and I am inclined to agree with them.

Putting a sleeve over it is a definite option but the sleeve would only cover the back of the tube where it emerges and I would still need to delete the coolant flow through the throttle body ( the little right angle barb )

The copper sounds tougher and I could braze that up but it sounds like more work than just deleting the tube and blocking the port off.

Basically if nobody can give me a good reason not to take a tap off the top of the front coolant outlet instead I am going to go for it. I could even leave the path through the throttle body in the circuit and just have one more split in that line. Probably even using the same barb. I would just section that metal part out of the current tube. I'd tap a hole in the aluminium cover. Put a barb in to that. Only problem I can see with this is that the coolant would have given up a bit more heat since it would have to come up through the manifold first.
 
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I wonder if you'd have an idle speed problem with a warm engine if you cut the coolant flow through the ISC valve (idle speed control or fast idle air valve) under the throttle body? As far as I know my pipework is original and not leaking with 190k miles on it and I've not seen any references to problems like yours until now.
 
This one has about 380'000 on it and the sign for me that something was up was that the tube has white marks painted on it by a previous mechanic. And at some of those points it is now indeed leaking. Like they -knew- this was a common problem.

It may also be that they fixed / improved the materials in the tube in later models. I've seen numerous examples of pictures now with coolant pooled up in the block. Sometimes it is this tube. Sometimes it is the head gaskets. Sometimes it is the welch plugs.

If it is this tube the leak can be quite small and hard to spot. Over months the block will just gradually develop a big puddle. Especially at the back where a deep hole is. The place to shine a torch is up at the back of the block where this tube exits. It will also collect up on the back of the transmission where it drips down.

I also wondered what deleting that circuit would do to the IAC as well. Perhaps I could find a middle ground where as suggested I cover the tube in a bit of rubber hose. The thing is the tube has brackets on it that prevent you from putting a sleeve the whole way over it. But I could definitely sleeve the back where it has leaked and delete the rusted barb.

But I am bit weary because the person who was in here before me clearly thought the tube was eventually going to leak all along the length. Has white dots on it in various places including where some of the leaks are.

I actually like the idea of deleting the barb off the side of the tube -and- then running a line to the throttle body from somewhere else.

Seems like reasonable compromise.
 
I’ve never understood using mild steel anywhere near water, period.

There are so many alternatives, at little extra cost, stainless steel, copper, a wide range of plastics, silicone, and other metal alloys.

I use my rear heater on the 80 and can see that the steel tubes feeding that will need to be replaced soon.

OK, they lasted 22 years, which isn’t bad going, but I’ll be replacing them with either rubber hoses or copper.
 
I guess if you replace the tube with a genuine Toyota one you should get another 380,000 (whatevers) out of it. And if you keep it and run Toyota Red, it may even last longer. This seems the easiest path to me and one that's going to outlast a lot of other parts. Assuming it's the original, of course.
 
Agree. That is the path of least resistance. We don't know if this tube has ever been replaced before. My guess is that at some service interval when it should have been replaced they just put white dots all over it in the places where it is leaking! So it could have been in here for the full 380'000 for all we know. I think I will make up a little cap at one end to seal the new one off and pressure test it. I might also paint it with an engine enamel or something else tough to help keep the moisture in/out.
 
Here are pictures of the tube. Still tempted to delete the t-join from the new tube and run a line from somewhere else.

leak01.jpg leak02.jpg leak03.jpg
 
Ho Damien,
The white marking spots are factory marking from 1th production, nothing else. I think your car ran on water for emergency sometime ago ? What happend is that chalk builts up beteren the hoses and fittings. By refill with purple-red coolant, this coolant is going to eat the chalk and resulting in al kinds of leaks. Losen the hoses and clean of the white-grey sludge of hose and hoseconector. Leave the pipe in Place, it’s the main to your heating. Leave the by pass to your throttle regulator. This parts sends temperature data to your ecu for use of choke / fuel oxigen cold engine. If you install a T at the end of the pipe for easier acces and checking, this can be done, if you want... good luck with it Greetz Jack
 
Yeah these were not the factory paint spots. The replacement one I have has those. These are like little twink marks. Literally over the leaks. Perhaps it could be something they put in the coolant that came through. Like stop leak. I had to clean the ports out of the block because some of them were blocked up with that crud. Totally flushed the block. Cleaned it all out. Redecked it. Did head gaskets. What was the original colour of the RTV used to seal it to the block I wonder. That might tell me if someone took it off and put it back on again.
 
Following up on this. What I did in the end was to engine enamel the entire tube and to drill a hole in the plate it is joined to just big enough to get a camera scope through so I can least peer in between the heads to see what is going on between them. That way I can check the whole tube now and again. Not just the back end of it.
 
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