AC condenser for Transmission cooler?

[Dishtowel]

I had a thought (don't worry, no-one was hurt) , I plan on using the AC compressor for on-board air, it's not a York or anything special, I'm just going to lube it when I use it. Since my rig came with AC and I have an AC condenser out in front that no longer has anything to do I am considering using is as a transmission fluid cooler.

I think it was quite a-bit of work for my A4LD (with 280,000km) to push my 32" rubber, and the day I blew a coolant line and nearly emptied it probably didn't help. But I'm at the beginning of my very own 5.0L swap. I have a AOD trans on my hands, I know the V8 will push 32"s (and 3.73 gears) with no problem, and if the A4LD could do it then I'm sure a AOD won't be bothered by them either.

I'm basically considering it because.... well why not? What would be the down side?
I need to buy and extra 2 liters of ATF?
My trans will run 'too cool'? (This rig will not be taken out in the winter, and is there such a thing as too cool trans temp?)
The heat from the AC condenser/trans cooler will adversely effect my engine cooling?

Has anybody else done this? Does anybody know some good reasons why I shouldn't?

 

[Will]

Under any conceivable circumstances there is no such thing as too cool of tranny fluid.

It could work. It's a big cooler though. It's possible there's too much resistance in it. I'd prefer a small one with a fan on it.

 

[Wicked_Sludge]

my only concern would be flow. im sure your trans supply lines flow more volume than a normally functioning a/c...i just dont know how much.

some will argue that there is no "too cool" for an auto tranny. i tend to disagree. however i dont think overcooling will be a problem with this setup.

i also wouldnt worry about the hot cooler in front of your radiator. they come like this from the factory on all kinds of vehicles.

 

[Dishtowel]

Resistance, something I never thought of. Well, I could bust out my fluid mechanics text and figure out how much of a pressure drop all those extra corners and tube will cause. Any automotive techs know how much PSI trans pumps put out? And how much they require to operate?
That could cause poor low rpm shifting I suppose.

 

[AllanD]

Actually there IS such a thing as "Too cool" tranny fluid but there's a real easy way to deal with that.... (I'll get to that in just a moment)

Yes, an A/C condenser makes a wonderful transmission cooler.

Now, to preventing the fluid from being "too cool"?

use a radiator with a tranny cooler built in and run the fluid through the coller built into the radiator AFTER it's run through the former A/C condenser.

This will make sure the tranny fluid is at the temperature of the engine coolant
being returned to the engine from the "cold side" of the radiator.

This is more or less the correct operating for the transmission.

AD

 

[thegoat4]

One thing: flush the hell out of the condensor core if it's anything other than pristine. Other than that, ought to work fine. Might also get one of those oil cooler regulators so your trans will get up to operating temp quickly. There is such a thing as too cool ATF: you'll get very rapid varnishing if it always runs cold.

Rubbing alcohol makes good AC flush.

 

[Will]

We've discussed this one before.

This is from Amsoil--they feel petroleum fluid is good from 10*F to 170*F with bordeline performance from -30*F to 270*F. I also researched other manufacturers sheets and this is concurred with. Thats why I said as a practical matter you can't overcool the fluid. The stuff isn't engine oil, it's already thin. It's hydraulic fluid.

 

[Will]

And don't run it through the auxillary cooler first--run it through the fluid-fluid one. The fact is, the fluid-fluid is more efficient than the fluid to air. Under most circumstances, the cooler in the radiator is going to bring it down to the coolant temperature--or close to it.

Imagine this--you are going up a hill pulling a trailer, your foot is to the floor and you are making 150hp. The converter clutch is unlocked and the converter is doing its job--multiplying torque--its slipping 10% probably.

It's the same thing as taking a 15hp engine, connecting it to a fluid churning device and running it to full power while the fluid churning around absorbs ALL that power. It's going to get nuclear hot and destroy the fluid. You ever do that calculation in physics class where if you shook a glass of water and none of the heat from the shaking was lost, how long would it take to boil the water? This is the same thing on a grand scale. The fluid temperature can very a hell of a lot depending on what you are doing. And the fluid needs to be fairly cool. That's why Ford and eveyone else puts the auxillary after the fluid-fluid exchanger. You want it to be cooler than the engine, not the same.

 

[LearjetMinako]

I concur with Will. Transmission fluid temps does need to be lower than the raditor temps. Ideally, a good transmission will not run hotter than 160*F and no hotter than 180*F under towing.

My father learnt this lesson the hard way. RIP one tranny after being cooked.

If you plan on making the tanny work harder. I suggest sythenic fluid.

 

[AllanD]

Will you are mistaken that the FLUID temperature is at issue when it is the temp of the metal parts and the seals inside the trans are more important.


Of COURSE Amsoil is going to say that pertoleum oil is only good to 170ish...

They sell synthetic!

IDEAL automatic transmission operating temp is about the temp of
the "cool" side of the radiator coolant.

use the air to oil cooler to cool the fluid as much as possible then use the water oil coolant to warm it back up to the PROPER temp.

On european cars with automatic transmissions there is typically an air-to-oil cooler,
but they usually use a bypass theromstat in the loop to bypass the cooler until the tranmission reaches PROPER operating temp.

And BTW, what temp do you THINK the "return" coolant from a properly sized radiator actually is?

My concern is NOT the temp of fluid when towing as much as it is the temp your transmission will drop to when the ambient temp is quite cool to downright COLD
and you ARE NOT towing which for anyone here is more typically the case....

Look carefully at the fluid flow path on ANY factory installation where both a
water-to-oil cooler AND an air-to-oil cooler are used.