Auxiliary trans cooler

The (40K)...is that the BTU rating? Those do look better than the Derale I was looking at.

My 4l80E equipped k2500 sub is getting cooked going up hills. It is currently in the shop draining the bank account.

My normal towing temps are below 190, as soon as it hits a hill, locked in 3rd (tow haul) (not bogged)and l it raises 40 degrees to 230f or higher.

I never saw anything over 200 with our old camper and it was around 7K lbs. Sounds like something wasn't right with yours maybe.

GeoBoy wrote:
I did some research and many people driving with a 4L80E are using a Tru-Cool 40K as a replacement for the stock cooler. When towing now the transmission temp runs about 160 degrees.

+1 for the above. I've got the 40K cooler on my 2500HD 6.0 and it keeps the 4L80E nice and cool towing in the mountains with the toy hauler.

It looks like the Tru-Cool addresses the cold weather issue too. I think I'll be ordering one soon.
Did you guys just use the stock lines from the factory cooler?

This is how I did mine...quick, easy and leak free.

Dont forget to go to napa and get the quick disconnect fittings for the cooler.

http://www.gmfullsize.com/forum/showpost.php?p=5008780&postcount=3

I decided to use the rubber line that came with the Tru-Cool, order an extra piece when you order the cooler, part #LNG-723. I used the fittings that came with the cooler that allows you to use the rubber line. I cut the aluminum crimp that is used to retain the OEM rubber line onto metal fitting coming out of the radiator, to the OEM cooler. The metal fitting coming out of the radiator, clamp the new rubber line and run the line to the fitting on the Tru-Cool and clamp. Then cut the aluminum crimp off the metal line going back to the transmission, remove the OEM rubber line, attach and clamp the new rubber line and run it to the other fitting on the Tru-Cool and clamp. I them put cable sheathing on the rubber lines to prevent abrasion.
I don't trust compression fittings and the OEM lines didn't really fit nicely using the suggested method in the GM forum post.
I used a rotary tool with a cutting disk to cut the aluminum crimps.
Bought the Tru-Cool and extra rubber line from Oregon Performance Transmission.
Good luck.