Should I add a transmission cooler?

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SecondMonkey

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I have a Jeep Cherokee with the unstopable AW4 automatic transmission. It has over 218,000 miles on it and still works as good as new.

Most of my driving is short trips, so nothing in the Jeep has much of a chance to heat up, let alone overheat. But then sometimes I drive a few hundred miles. I do not tow anything.

So the question is, SHOULD I add an external tranny cooler? I happen to have a spare cooler already, it's just a matter of installing it. But, I may end up with an OVER cooling problem.

If the answer is yes, should I install the cooler BEFORE the radiator/ATF heat exchanger, or AFTER?

My only point for this is that I want my old transmission to last as long as possible.
 
I don't think you really need it but if you do put it in it goes AFTER the radiator. Driving a few hundred miles is no big deal, towing is another matter.
 
I say add the cooler after the factory cooler. This is how it is done on oem towing packages. If you see a lot of extreme cold temps in the winter, I would be inclined to use a full synthetic ATF for better cold flow. Add an inline magnefine filter to keep the fluid clean. I have yet to replace a trans that was upgraded like this. Unless your ECU won't let you get top gear or converter lock-up due to cold fluid, you should have no problems with overcooling. Worst that could happen is you would lose fuel economy if not in lock-up or high gear.
 
IMO, the oil-to-air cooler should be installed BEFORE the oil-to-water cooler.

This opens up a big can of worms... debate has raged on this forum for pages at a time over this issue.

But IMO, you will get maximum heat transfer by exposing the ATF to the air when it's the hottest... and you will introduce less heat into the cooling system this way. I don't know which 'oem towing packages' bmwtechguy is talking about... but he's likely right in some applications. But in heavy trucks with allison transmissions, in cases where there are two coolers, the ATF is routed through the oil-to-air cooler first, then into the oil-to-water cooler.
 
I used to drive a 94 Ford E250 around NYC every day. I put lots of miles on it and when the trans needed to be rebuilt, I added a heat sink type cooler to it before the factory cooler. Also added an inline spin on filter. That transmission performed better than any other truck trans I ever had for a longer time. I DID tow with it, but I can count the times on one hand. I left the company 5 years ago and I know they still have that van.
 
uhhmn, IIRC, the extra cooler I added is after the radiator. Which is the better hookup, IDK. I added it because I had it. and like the idea of adding an extra qt to the ATF.
 
The only reason I added it before the factory cooler was to hopefully add less heat from the trans into the cooling system. I never tested the theory, but I do have a similar cooler on my Yukon set up the same way. I'll check the lines with my raytec and report back.
 
Well, here's my theory:

If I install the external cooler BEFORE the factory cooler, the ATF-coolant heat exchanger can either keep cooling, or HEAT up the trans as needed and keep it around 200*.

Wouldn't that create a more even temp inside the trans under all types of driving?
 
Originally Posted By: SecondMonkey
Well, here's my theory:

If I install the external cooler BEFORE the factory cooler, the ATF-coolant heat exchanger can either keep cooling, or HEAT up the trans as needed and keep it around 200*.

Wouldn't that create a more even temp inside the trans under all types of driving?


Yep. And that's probably why GMC routed the transmission fluid this way on their Top Kick medium duty trucks.
 
My engine coolant temp sensor is before the radiator. The water in the end tank where the coolers typically go is warm but I can hold my finger in it indefinately. It's not nearly as hot as the engine temp.

It's pretty hard to overcool a trans. Unless you live in an extremely cold climate I would put the external cooler after the radiator cooler.
 
If you look at the OEM aux trans coolers on most passenger vehicles such as the ones with a "towing package" you will find that the fluid is nearly always routed thtough the radiator cooler first, then the air/oil radiator (aux cooler) next, then back to the trans. I live in a warmer climate and have always added an aux cooler in series the same as oem set-ups. I think I can be confident that the ATF will always run at cooler temp than before adding the aux unit. After changing/flushing ATF on literally hundreds of vehicles (passenger cars and trucks), I have seen the fluid flow the way described above. I see no real problem routing it before the radiator as others have said, and it may actually be better in cold climates to maintain a steadier ATF operating temp. I just have never done it that way.

I have been told that to replace the cooling capacity of the liquid/oil heat exchanger in the radiator requires a substantially large air/oil external ATF cooler. I mention this after reading the TCI link which promotes bypassing the radiator cooler, probably to prevent any leftover cooler trash from getting into the newly rebuilt trans.
 
My younger brother has a 65 Pontiac Tempest with a warmed up 327 Chevy and a TH350 trans. The trans is all worked with a loose converter, shift kit, all the tricks. He runs a big Earl's cooler on the front, no radiator cooler and a Derale pan with cooling tubes running right through the pan. I think that trans is in that car 18 years and still works mint.

I had an 80 Trans Am with a 383 Chevy and a 700R4. I also ran an external cooler but I used the radiator cooler as well. My pan was cast aluminum with cooling fins.
Both transmissions lasted a good long time, so I don't believe it's possible to harm an automatic by overcooling it. BTW, I drove the T/A year round, so sometimes it saw temps of zero degrees F.
 
I put a transmission filter on my 1962 Pontiac Catalina and since it had a temperature sensor fitting, I added a gauge too. The next week I bought an air/oil cooler and added it in after the radiator. I then saw temps drop from over 225+ Deg. F. to 180-190 in the summertime. I don't know if the transmission was actually happier but I was.
 
Originally Posted By: daves66nova
never heard of over cooling an auto trans.


I wish I still had the pictures...
ATF can gel in winter and starve the trans. These are by far the the worse trans failures I have ever seen. Total meltdown!
Only a concern in harsh winter climates (Minnesota, Dakotas, Canadian prairies and more northern)

I always install the AUX cooler before the in rad cooler.
 
The transmission is designed to operate in a particular temperature
range. If the fluid is too cool the pressures will be higher in the trans. install before radiator, if trans is overheating it will lower the fluid temp and the radiator will put the temp in the sweet spot it was designed to run in.
 
Another point to ponder.
Say you plumb your aux trans cooler after the rad and mount it in front of the A/C coil.

For ease of numbers, let's say that the aux trans cooler is throwing off 100btu as the air moves through it. That 100btu is now being added to the A/C coil which makes it less cool. Now that 100btu from the aux trans cooler and what ever the A/C coil adds to that 100btu is now trying to cool the rad.

A non-scientific minds wants to know ... is adding the aux trans cooler in the up-stream airflow of the other "heat exchangers" really a good idea?

Hummmmm
 
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