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Discussion Starter #1
I know the heat exchanger in the radiator, for an auto transmission, is said to both warm and cool the ATF. I have not found anyone who seems to know to what extent the warming-function is important.

I know no warming happens until the thermostat opens and the radiator comes to temperature; and, I know once the AT really gets working, it produces ATF which is hotter than the coolant. So, it seems to me that the warming only happens for a relatively short period of time.

But, is the warming important to the AT performance or longevity?

I am writing because I am thinking of by-passing the heat exchanger and adding a second air/ATF cooler. I don't like the idea of my ATF flowing unseen through my radiator. A good number of people with my truck have experienced exchanger failure and ended up with coolant-filled dead transmissions.

2003 Tundra

Thanks,

Roy
 

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The only real way to see where the coolant temps and transmission temps are in reference to each other is to log and graph them. I do know that my transmission in my T-100 will not shift to the upper gears until the coolant temp is about 131 degrees Fahrenheit.

I do know that a liquid heat echanger is more efficient than an air heat exchanger even with an active fan in the air heat exchanger. Keep in mind that auto makers try to make the system foolproof as cheaply and simply as possible.

Yer ATF will require more cooling during the initial roll of yer vehicle than when the torque converter locks up. You can see this when the ATF temps spike as you start out. Any air heat exchanger will need to be able to handle this spike rather quickly and efficiently or the heat will start to build and degrade the ATF and components if the temps git too high fer too long. If you tow a lot or do a lot of skinny pedal exercises, then I would expect you may need a pretty sizable air heat exchanger. ;)

Good luck with yer experiment! ;)
 

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The cooling lines for ATF only run in a small part of the larger heat exchanger/radiator, and it's really just to provide some cooling for the transmission fluid rather than just being dependent on the air flowing through the engine compartment and under the vehicle.

It really doesn't provide much of a warming function, but in some cases, such as in freezing cold weather, it would keep the fluid warm if the transmission wasn't producing a lot of heat, during light use or with a lot of idling.


It's not uncommon to add a larger, dedicated transmission fluid cooler, and sure, you can even just use the dedicated heat exchanger for the transmission.

Sometimes the trans fluid cooler lines in the radiator are repurposed as an engine oil cooler instead, or you can just cap them off and not use that part for anything. Just be sure to cap them off and not leave it open to water and corrosion - it'd be a good idea to have the ability to switch the ATF cooler lines back over to the radiator cooler in case of a leak or damage to the dedicated cooler, or just if you ever sell the vehicle or if someone else wants to put it back to stock.
 

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The only real way to see where the coolant temps and transmission temps are in reference to each other is to log and graph them.
^ This is my conclusion, too.

and it's really just to provide some cooling for the transmission fluid rather than just being dependent on the air flowing through the engine compartment and under the vehicle.

It really doesn't provide much of a warming function
^ Another of my conclusions.

The truck in question came stock with the ATF/Coolant and ATF/air heat exchangers. I understand the efficiency of liquid/liquid exchangers.

I plan to to the temp monitoring/graphing to figure out what exactly the ATF/coolant exchanger is doing for me.
 

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The cooling lines for ATF only run in a small part of the larger heat exchanger/radiator, and it's really just to provide some cooling for the transmission fluid rather than just being dependent on the air flowing through the engine compartment and under the vehicle.

It really doesn't provide much of a warming function, but in some cases, such as in freezing cold weather, it would keep the fluid warm if the transmission wasn't producing a lot of heat, during light use or with a lot of idling.


It's not uncommon to add a larger, dedicated transmission fluid cooler, and sure, you can even just use the dedicated heat exchanger for the transmission.
Ditching the in-radiator trans cooler for an aftermarket cooler can be a good move. The trans cooler line inside the radiator can fail, then you have trans fluid and engine coolant mixing in both the trans and engine, That's a huge repair bill.
 

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Discussion Starter #7
Ditching the in-radiator trans cooler for an aftermarket cooler can be a good move. The trans cooler line inside the radiator can fail, then you have trans fluid and engine coolant mixing in both the trans and engine, That's a huge repair bill.
That is what I am worried about. If owned a Nissan 4.0, I would have done it yesterday (high rate of failure). I am unsure about my Tundra...I have run into, in person and on-line, a few folks who have had this failure. Not sure that level of risk justifies the change. On the other hand, if it were to happen, it would drive me nuts, as it is a known-to-me risk.

Roy
 

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Discussion Starter #8
BTW, there are Nissan dudes who just by-pass the coolant/ATF exchanger without adding a second air/ATF exchanger. The reports I've read, say they are not getting excessive tranny temps.
 

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BTW, there are Nissan dudes who just by-pass the coolant/ATF exchanger without adding a second air/ATF exchanger. The reports I've read, say they are not getting excessive tranny temps.
I'm not even going to comment on that.
 
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