Anyone experienced an overheating auto transmission when towing? (1 Viewer)

[KiwiBogan]

Occasionally when towing bigger trailers (1.5-2.5T), I very intermittently experience odd behavior, most obvious being like the car becomes speed restricted to 80-90km/h, overdrive seems to not work for a period. I swear its due to the auto transmission overheating but I have no way to tell for sure and am curious if it could be something else like high intake temperatures causing fuel reduction from the ECU or something. My EGTs and Coolant temps are always well in the safe zone when this occurs. It usually happens when driving in warmer weather but that may just coincide with when we go away on long drives/holidays. I do run 16-18psi boost so my intake temps are running a bit high (about 50-60 deg C above ambient) and I thought on our last trip maybe it was when the intake temps were hitting 80 deg C, the problem was occurring but it was too hard to tell for sure as there were other things at play too i.e. strong winds

Anyone else experience such things?

 

[Morrtac]

Do you have an external cooler, or the one that is in the radiator?

 

[KiwiBogan]

Do you have an external cooler, or the one that is in the radiator?

Radiator cooler. I did try an external one but had some issues with it leaking so removed it from the system again. Do you think they actually make a difference? I didn't think mine did

 

[Morrtac]

Radiator cooler. I did try an external one but had some issues with it leaking so removed it from the system again. Do you think they actually make a difference? I didn't think mine did

I bypassed my in-radiator cooler and installed a large Hayden 679 cooler. I don't want a leak to turn my transmission oil to milkshake. Plus I'm adding an AL radiator and it doesn't have the internal one. (Might change to the 699, has the bypass valve... I live in warmer climate so IDK)

 

[KiwiBogan]

I bypassed my in-radiator cooler and installed a large Hayden 689 cooler. I don't want a leak to turn my transmission oil to milkshake. Plus I'm adding an AL radiator and it doesn't have the internal one.

I think that whole radiator leak/turning to milkshake thing is a myth, or at very least an isolated incident someone experienced and shared, due to a very neglected radiator/engine. I'm really not sure I support the idea of excluding the radiator from the trans cooling system. I mean, my coolant temps never got at absolute worst over about 90°c in the heat of the day (35°c) towing into a partial head wind. Turbo up. Fuel up. I was working it pretty hard! So that would suggest the trans isn't getting any hotter than that no? Also when I had my trans filter changed recently, apparently it all looked pretty clean in there and in good condition. No burnt fluid or crap in the pan. So if this is true, OEM spec radiator and cooling system set-up is the way to go. Piss off the old radiator, pop in a new one every few years and you should be alright. I'm also not convinced an Ali radiator will help. I've read in the Patrol forums that in some cases they've been worse and people have removed them again. Worth reconsidering!

 

[Morrtac]

I think that whole radiator leak/turning to milkshake thing is a myth, or at very least an isolated incident someone experienced and shared, due to a very neglected radiator/engine. I'm really not sure I support the idea of excluding the radiator from the trans cooling system. I mean, my coolant temps never got at absolute worst over about 90°c in the heat of the day (35°c) towing into a partial head wind. Turbo up. Fuel up. I was working it pretty hard! So that would suggest the trans isn't getting any hotter than that no? Also when I had my trans filter changed recently, apparently it all looked pretty clean in there and in good condition. No burnt fluid or crap in the pan. So if this is true, OEM spec radiator and cooling system set-up is the way to go. Piss off the old radiator, pop in a new one every few years and you should be alright. I'm also not convinced an Ali radiator will help. I've read in the Patrol forums that in some cases they've been worse and people have removed them again. Worth reconsidering!

True enough, i dont know about the milkshake thing really. But I can tell my Rad is about to go...Original, browning plasic, micro cracking all along the top plastic tank. I'm going with a KoyoRad triple pass designed for a V6 4Runner, not some knockoff junk. I will have to do some custom hose work to fit it up.

 

[KiwiBogan]

True enough, i dont know about the milkshake thing really. But I can tell my Rad is about to go...Original, browning plasic, micro cracking all along the top plastic tank. I'm going with a KoyoRad triple pass designed for a V6 4Runner, not some knockoff junk. I will have to do some custom hose work to fit it up.

Yeah cool. Get that old thing out asap haha! I had one like that let go on me once on the highway. Coolant all drained and engine cooked before the temp gauge had a chance to react haha. Good times! I went with a Koyorad too. OEM equivalent. Couldn't be happier with it!

 

[mjosoba]

I think that whole radiator leak/turning to milkshake thing is a myth, or at very least an isolated incident someone experienced and shared, due to a very neglected radiator/engine. I'm really not sure I support the idea of excluding the radiator from the trans cooling system. I mean, my coolant temps never got at absolute worst over about 90°c in the heat of the day (35°c) towing into a partial head wind. Turbo up. Fuel up. I was working it pretty hard! So that would suggest the trans isn't getting any hotter than that no? Also when I had my trans filter changed recently, apparently it all looked pretty clean in there and in good condition. No burnt fluid or crap in the pan. So if this is true, OEM spec radiator and cooling system set-up is the way to go. Piss off the old radiator, pop in a new one every few years and you should be alright. I'm also not convinced an Ali radiator will help. I've read in the Patrol forums that in some cases they've been worse and people have removed them again. Worth reconsidering!

It’s definitely not a myth. And the radiator transmission cooler is not a cooler at all. It’s there to warm your ATF to achieve lockup more quickly when it’s cold. I’ve bypassed mine, and it takes a out 10 minutes longer when it’s cold to get the ATF up to temp. An external cooler will greatly increase your transmission/transmission fluid lifespan.

 

[KiwiBogan]

It’s definitely not a myth. And the radiator transmission cooler is not a cooler at all. It’s there to warm your ATF to achieve lockup more quickly when it’s cold. I’ve bypassed mine, and it takes a out 10 minutes longer when it’s cold to get the ATF up to temp. An external cooler will greatly increase your transmission/transmission fluid lifespan.

I haven't read of anyone actually have it happen to them, only people worried about it happening to them. If you ever stumbled across any threads on it where it has happened to someone, feel free to share. I'd like to learn more about it.

From my experience with an external cooler, it made no difference other than create extra points for potential leaks/failures. Mine failed (not catastrophic) from inadequate mounting. Off roading vibrations caused a leak. So make sure you mount it really well when you do yours.

 

[mjosoba]

I’ve just always used the stock ones on the 80’s. The early A440’s in the 62’s didn’t have external coolers and would often have problems when used hard. Toyota put them on all 80’s with autos thereafter. There’s a direct and demonstrable correlation between fluid temps being lower with external coolers, and lower temps lead to longer life.

I’ve had that happen on two of my rigs. Fortunately caught it very quickly.

 

[KiwiBogan]

I’ve just always used the stock ones on the 80’s. The early A440’s in the 62’s didn’t have external coolers and would often have problems when used hard. Toyota put them on all 80’s with autos thereafter. There’s a direct and demonstrable correlation between fluid temps being lower with external coolers, and lower temps lead to longer life.

I’ve had that happen on two of my rigs. Fortunately caught it very quickly.

Hmm interesting. I did a quick search specifically on the A432F trans in particular. Found some heated debate for and against the external coolers. I'm still on the fence at this point haha. Seems like there's a bit more to it than I thought. So what are the symptoms you've experienced of this trans overheating? Does it line up with my symptoms would you say?

 

[mjosoba]

Hmm interesting. I did a quick search specifically on the A432F trans in particular. Found some heated debate for and against the external coolers. I'm still on the fence at this point haha. Seems like there's a bit more to it than I thought. So what are the symptoms you've experienced of this trans overheating? Does it line up with my symptoms would you say?

No, I’ve not had any issues, but mine have been the A440 and the A442. They both have external coolers. The only transmission I’ve had an issue with was a 700r4 and it went away after a fluid swap and adding a cooler. Average temps went to under 200 and had been up in the 230 plus range.

Does yours have the same as the later 80’s? The A343? All of the 80’s had external coolers stock.

 

[KiwiBogan]

No, I’ve not had any issues, but mine have been the A440 and the A442. They both have external coolers. The only transmission I’ve had an issue with was a 700r4 and it went away after a fluid swap and adding a cooler. Average temps went to under 200 and had been up in the 230 plus range.

Does yours have the same as the later 80’s? The A343? All of the 80’s had external coolers stock.

Yes mine the A343F. Though the 95 series Prado is about a tonne lighter than an 80 series. Maybe that's why they excluded the external cooler? No need for it?

My trans as just on 400k kms on it and is still going strong. I've pulled 2.5T with it for a 3 week tour with days getting up to 40°c. This is when I first noticed the restricted speed thing in my OP happening. Done an AT fluid drop and filter change and no signs over overheating according to the mechanic. So it's baffling my brain this one! Maybe my problem is to do with intake temps and not trans.