I have a '99 2500 4x4 with a 6 liter and 4RL80E. I have eliminated the in-radiator cooler and installed the largest cooler PermaCool makes in front of the radiator and the largest cooler B&M makes with its own fan under the chassis. I tow a 15,000 5th wheel trailer. Yes, I know I'm towing way beyond the rated capacity but the truck handles the weight surprizingly well. Cruising down the road brings the trans fluid up to190 to200 degrees but long grades force me to pull off the road at 260 (the trans goes into its fail safe mode). As far as I know this is the same transmission used in much larger trucks with gas engines. Why then does mine seem un-coolable? I've spoken to several so called trans gurus but no one has even a guess. I'm not inclined to replace the transmission without some idea that it will make any difference. Any thoughts?

 

Might be the coolnt pump

 

Thanks. I guess I should have mentioned that I have already performs all of the tests listed in the Chevy service manual for this transmission. The flow through the cooler lines is a little more than the books calls for which rules out the pump, various relief valves, and the posibility of constricted oil passages. The transmission shifts exactly like it is supposed to so I'm currious if the culprit could be the converter. It seems to do what it is supposed to do but I know that is the source of all heat.

 

if its ok empty...i'd say your pulling too much.

a 4l80e is not considered tre biggest and baddest..allison is

 

I agree with Argon, they put allisons in the big boys for a reason. No amount of cooling will get that transmission to pull that much weight. Only other thing you could do is build up your current trans as much as you can with a shift kit, towing-type torque converter, etc.....but even then there is no guarantee.