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Transmission Flush When Also Changing Radiator

stuzbot

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I brought this up in my 'Got One at Last!' thread:


But it's got a bit lost in the midst of all my other froth-lipped tomfoolery there. So, since it's an important job I don't want to screw up, I'll put it in a separate thread.

I've ordered a new radiator, new transmission filter & gasket and plenty of ATF and coolant from Roughtrax, as I'm going to preventatively overhaul my entire cooling system.

Now, I've read the various threads about draining the transmission sump, refilling, driving a bit to allow the new ATF to dilute the old cruddy stuff.... rinse and repeat until you've purified your ATF as much as possible. But I still have some queries about what I'm planning

1: If I remove and replace radiator too, I'll obviously lose whatever ATF was in the oil cooler section of the old radiator, as well as what was in the transmission sump. So is it just a case of topping up with that much extra to get back to where I was, or is it more involved. ie does the oil cooler section of the new radiator need to be primed or bled to remove the air and fill it with ATF, or will gravity do the trick?

2: Fitting the new transmission filter means removing the transmission sump. Will this also eject more of the old cruddy ATF than comes out the drain plug? I imagine it will. And, when I remove the old filter, will that cause even more old ATF to drain out? Just trying to get a handle on how much capacity I'll be needing in my catching tub to cope with it all.
 

MODVRS

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I think you may be overly concerned about the job. It's a simple old-fashioned system so you're not going to have a problem with air locks, the fluid will go where it needs to.

Experiences vary on what drains out from 2 litres to 5 litres (I've had 5 litres out both times I've done the job so advise a big drain pan). You'll only get dribbles from the trans, filter and cooler when you pull them off; most of what you get will come out of the drain plug.

Refilling is more of a faff as you need to be precise and get the level spot on. It's measured with the ATF warm and the engine running in neutral or park using the "hot" level on the dipstick which can be hard to judge. As I'm happy I've got the level right once and have no leaks I just measure everything that comes out and put the same back in with a final sanity check on the dipstick (level ground obvs.)

Good luck.
 

AdventureWagon

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Budget for 5l to come out maybe a little more if overfilled. Don't worry about the cooler it's self bleeding and less than 1l including the lines (my guess). The cooler drains into the sump when the engine is stopped.

Refilling accurately is a PITA at least on mine. But if you get out about 3 to 4 litres then safe to refill with that. Especially if you don't plan on towing then that will be cool. If you do you'll want to pay much closer attention to it.

Removing the pan won't get you much more out but you will be able to clean the pan and magnets. It will rain ATF though so be prepped to get yourself and driveway covered in it.
 

Juddian

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Agree with the above, 4/5 litres has been what i've got from both 90 and 120 series autobox sumps.
 

AdventureWagon

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Also be prepared to wipe and dip about 20+ times to check the level. Maybe something about my car or the 5VZ engine bay layout but I found it very hard to get a reliable repeatable reading on the trans dipstick.
 

stuzbot

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Also be prepared to wipe and dip about 20+ times to check the level. Maybe something about my car or the 5VZ engine bay layout but I found it very hard to get a reliable repeatable reading on the trans dipstick.

Funnily enough, I just had a quick dip and look at the transmission fluid pre-buying and then again a couple of days ago, to compare the colour with that chart above and, both times, I found it really hard to tell where the level was. It just seemed to be smeared halfway up the stick. So either my transmission is ridiculously overfilled, or I've just not got my eye in yet.

As regards my forthcoming ATF and radiator overhaul, I'm thinking now that, rather than trying to do everything at once, baby steps are the order of the day. Especially after watching this guy's video where he actually explains why a full-scale flush on a high mileage transmission can sometimes cause problems, rather than just repeating the urban myth with no explanation.


So, since mine's on 200.000 miles and I have no service history relating to the transmission, I reckon it's probably better if I use the 'change ATF. Drive for a while making sure everything's OK...rinse and repeat until fluid is nice and red again' rather than giving it a full scale ATF enema straight off.

Mind you, as the Yang to the above guy's Ying, this lad's recommending just going 'full flush and damn the consequences!' Though his argument in favour seems less scientifically based and more akin to "Go on. Spark up! My grandad smoked 100 a day for 90 years and died on the job, on his 105th birthday!

 
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AdventureWagon

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When the motor is off it will appear overfilled, as the fluid drains out of the transmission internals, especially over time. However my theory is that surface tension holds this in the dipstick tube somewhat even after it's started up so getting an accurate reading is quite hard. This is made extra hard if you're in the process of filling and then dipping as you've just filled the tube with cold thick fluid.

TBH I think though you could still do the radiator part of the overhaul, as if the radiator does fail you're up for a tranny rebuild anyway. As part of this you're likely to lose about 1l of transmission fluid which you can capture and assess and decide if you want to do a full service or not. After all if it fails after just replacing 1l of fluid then it was going to fail pretty soon anyway.
 

stuzbot

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TBH I think though you could still do the radiator part of the overhaul, as if the radiator does fail you're up for a tranny rebuild anyway....

I'm going to replace the radiator anyway. I've got a new one on order. Should arrive today actually. I was just thinking it might be better to only introduce one variable at a time. But I guess you're right. If the tranny blows up after replacing an extra litre or so, it was on borrowed time anyway.

Boy, I'll be glad when I get all these 'new motor preventative medicine' jobs out of the way and can start thinking about the fun stuff!
 

AdventureWagon

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Sounds a good plan. If you give them a little love these are pretty solid reliable trucks.
 
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