6L80E T Stat

Drivetrain discussion including Transmission, Differential, Driveshaft, and related items.
s/c'd cav
Posts: 1382
Joined: Mon May 30, 2016 3:12 am
Location: PHOENIX AZ

Re: 6L80E T Stat

Post by s/c'd cav »

kevink wrote: Tue Mar 03, 2020 11:21 am
s/c'd cav wrote: Mon Mar 02, 2020 10:35 am yes they have a thermostatic bypass at the trans cooler , it loops the trans fluid back to the trans by passing the cooler , until its up to temp
Really? I replaced the factory cooler on my 2011 with a bigger unit and didn't see a bypass. Where exactly is the bypass located and does anyone know what temp it's set to?
on the 11 it looks to be down below the rubber lines , kinda below the lower bumper beam , where its kinda out of site
9C1fanatic
Posts: 430
Joined: Tue Dec 30, 2014 8:58 pm
Location: Texas Hill Country

Re: 6L80E T Stat

Post by 9C1fanatic »

Its likely inside the block on top of the air to oil cooler where the lines go in. There is no sensor, its a mechanical t stat like the engine uses. When the fluid reaches a certain temp, the vale opens allowing ATF to flow through the cooler. Sounds like a better design then the K2XX trucks have on the 6L80E where the T-is at the transmission housing where the lines connect under the truck and before the T-stat opens, there is no flow at all to either ATF cooler. At least on the Caprice, it sounds like the ATF will still run the radiator tank loop when the air to oil cooler is bypassed. Good to know.

I wish someone could definitively say why a t-stat is being installed by GM. Ive been told the GMT 900 trucks with the 6L80E do not have any kind of thermostat. What is harmed by the trans not being a certain temp or warming up too slow. I also have guy feeling that the shifting complaints that come with all of these newer transmissions after the hydromatic series (4L60E etc) is somewhat being addressed by GM by trying to keep the trans fluid in a narrow temp range (about 200 degrees). Problem is this is causing dangerously high temps in the truck world on the 1500's when towing in some scenarios. I wonder if the same can be true for the Caprice? We have had a few Caprices at work lose transmissions around the 40-50k mark. This is the exception to the rule but since they don't get trans services till about 45k or so, I wonder if some of these failures can be blamed on fluid failure due to excessive heat. Its hard to know since there is no trans temp read out but as we all know, the hotter the fluid, the life of the fluid starts to fall off rapidly and once that happens, trans failure will follow. Had these specific cars been serviced earlier maybe the failures would not have happened.
Garner Ames



1975 Pontiac Grand Am L77 - 14.82 @ 92.89
1991 Chevrolet C1500 L31 Vortec/5 Speed
2002 Chevrolet Suburban 1500 LM7
2014 Chevrolet Caprice 9C1 L77 - 13.60 @ 105.87
2019 Chevrolet Express 3500 L96
Post Reply