A year ago I bought a transmission cooler. But, since my Suburban had the factory tow package with an oil cooler I didn't install it. There was a lively discussion on RV.NET where some folks argued that you could over cool your transmission. I read in the FAQ on etrailer.com that you cannot over cool a transmission and that adding a big cooler (or supplemental) will not hurt a thing. So, last weekend I installed it. The fluid now runs from the radiator, through the factory cooler, through the aftermarket cooler then back to the transmission. I took it for a long drive and then felt the new cooler, it was quite warm indicating that it's working. That 4L60e needs all the help it can get for towing, or so I have been led to believe. I use the burb for towing my travel trailer (5800 dry).

 

Chrysler found out in their early minivans that you can actually over cool transmission fluid. Some of the minivans in colder climates such as Minnesota actually slushed the transmission fluid because it got too cold. The fix was to put a thermostat in the transmission cooler line. Another way to avoid this would be to run the cool transmission fluid through the radiator transmission cooler and then back to the transmission. That would ensure a minimum temperature for the fluid then.

 

you do want it to run through the rad first.

on the duramax engines in very cold climates the trans were overheating due to not being able to flow trans fluid thru the cooler due to the shear/friction of trying to push cold fluid through the lines to the cooler...cold climate reprogramming was required.

in new trucks they run heat exchangers to heat the fluid...the faster its up to temp, the lower the friction, less for the dual stage trans oil pumps...= better fuel mileage. dodge is even running coolant pipes to the rear diff fluid to heat it up.

my transmission rebuilder instructor always said...if the trans is running hot with the factory cooler...your pulling to much...overloading the trans...to much for what it was designed for....get a bigger truck.

 

Found this graph years ago. Very informative on the connection between heat and tranny life.

https://d9hhrg4mnvzow.cloudfront.net...t0cz000000.jpg

 

That graphic is old and completely obsolete. Normal operating temperatures for DexVI transmissions are 190-200°F. And on the GMT900 trucks, the "Trans hot, idle engine" warning only comes on at 265°.

DexVI doesn't even start to break down until it's over 275°. That's a substantial improvement over DexIII.

I was concerned about elevated transmission temperatures I was seeing on my 2500 when towing in the Rockies. I have a good friend who is a transmission validation engineer for GM. He works at the Milford proving grounds. When he was first hired at GM, the first transmission validation he worked on was the 6L80/6L90. I expressed my concerns to him and his reply was simply, "We did a lot worse during validation." With a wink and a nod.

I've done this to my truck several times. The only extra TLC I give it is more frequent fluid changes. 179k miles, original engine and transmission, and it still runs/shifts perfectly.


My current rig - 8600 lb trailer

 

I don't see anything in the graph that is inconsistent with what you said.

 

Well, for one, it says that a transmission running at 200° won't even last 100,000 miles. I think there are a few million GM truck owners that might disagree.

 

i agree with the graph if it said fluid life not trans life.

How can anyone accurately knows the average temp of your trans fluid over a mileage interval...change it at the severe use maintenance scedule interval.