4l80e Issue

texaco50s · August 10, 2010

Hello All !

I'm hoping to find someone with a long-time tech background on this model transmission; perhaps dealership tech. Have a '00 K3500 CC 4x4 dually that has developed a overheating problem that seems to defy diagnosis. From discussions with some local mechanics this apparently is not unique but also not widely known. Have owned vehicle since new & currently has 17K on it. Problem began around 7K. Appears to be sensitive to ambient temps above 40-50 degrees. Below that temps stay in normal range. Had local trans guy I've known for years & who has done several transmissions rebuild unit. It had upgrades to improve durability done in addition to a new & better converter than factory uses. Truck runs & shifts out fine but problem remains that I can't use truck to tow or haul.

Just spoke with another mechanic last week who knows or two other trucks with same problem and told they could not find source of problem but that transmissions were replaced with GM "crate" transmission (later model 4L80E ??) and problem was fixed.

I'm abbreviating this up some to get to the point here. I've read posts on other forums where guys have had same issue & even done what I would normally think of next which is to put a larger cooler on. They still had problem after doing so.

OK, so the question is: does anyone know exactly what is cause of this mystery 4L80E overheating????

Please advise. Thanks!!

[email protected] · August 10, 2010

When mine started doing that I believe it was torque converter slip causing the tranny to shift hard also after heating up and increasing line pressure to offset the slip. Anyway I poured lucas trans fix in mine and have been another 20k miles without a single problem. Mine may have just been overfilled and foaming the fluid also.