Well, I might be in trouble with this post. I can't find a Toyota forum with the kind of quality posters I find here.

My question is not make-specific.

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.

Thanks, in advance, for being tolerant of my Toyota post.

Roy

 

I've heard many folks refer to the "warming" function of the heat exchanger in the radiator, but I rather doubt any significant warming effect happens relative to the ATF. The thing is, unless you're letting your car warm up for along period of time (a bad idea; hard on the engine), the ATF will start getting warm almost immediately following putting the transmission in gear, and as a result, the ATF going through the radiator before the thermostat opens will be warmer than the coolant. Once the thermostat opens, the radiator doesn't immediately heat up to 180°, it gradually warms up, and as such, I suspect the window where the coolant is actually warmer than the ATF can be measured in minutes, if that long.

Long story short, I would have zero issues with eliminating the heat exchanger in the radiator and replacing it with an in-line heat exchanger.

 

That is where I am heading, too, Shipo.

I know guys with the Nissan 4.0 have been replacing radiators or by-passing their heat exchangers in large numbers. Clearly the threat is less for my Toyota...but, I just ran into two guys, each with my truck, who both lost their transmissions at ~150k due to coolant-in-the-tranny.

Roy

 

For my part, I do everything in my power to drive cars which do not have an ATF to Coolant heat exchanger; that said, I do everything in my power to drive cars which don't even use ATF.

 

Me, too.

Finding my Tundra was a multi-year search. As you know from NH, Maine is in the Deep Rust Belt. Crazy hard to find the right truck/car. So, I take a few things in a vehicle which I really really don't like. My Tundra has an AT, timing belt, 32-frickin-valves, V8, electric-controlled transfer case...all stuff I don't like. It also has no rust, 117k miles, and it is a Toyota.

I am planning on a cooling drain/fill this summer. Unless I can find someone who can talk me out of it, I will do a heat exchanger by-pass then. I'll add an air/ATF cooler and a AT temp gauge.

Roy

 

Older Hondas sent the transmission fluid through the ATF cooler that was part of the radiator. With that set-up, it’s main function was cooling the fluid, not warming it.


Newer Honda models added a transmission warmer and changed the way the cooling lines run. The ATF or CVT Fluid Warmer uses the heat of the engine coolant (which warms more quickly after a cold start-up) to help bring the ATF/CVT up to operating temperature faster. -- The cooling lines run from the water outlet housing (thermostat housing) on the engine block to the inlet on the warmer and back to the thermostat housing. I believe the warmer also serves the dual purpose to cool too.

 

Do you think the warming is related to transmission performance or longevity? Even with the newer version, which you describe, the warming only happens until the time that the transmission is generating its own heat.

Roy

 

My understanding was the warmer was added to cure some cold-start hard shifting. Thinking about another thread on an Acura site, some cars were actually retrofitted with the warmer after owners complained about harsh shifts.

 

I would say for performance with the warmer. Even on some of the newer Honda Pilots with a fluid warmer, a separate OEM transmission cooler was added to certain trim levels.

 

Well, currently, at Maine winter temps, I start my truck and drive right off. No unpleasant shifting that I can detect...and, this is with the "old style" ATF-through-radiator which means my ATF is cold until the radiator comes to engine temperature.

Maybe newer, or higher-performance, transmissions have tighter tolerances for ATF temperature.