New 8 Speed Trans Temperature

Stoddard · March 3, 2015

Hey guys I was wondering if anyone would post your trans temps and driving atmosphere. It seems like my transmission is running warm to what I would expect.

Mileage on truck: 2200 miles

Trip type: 5hr interstate 70-80mph

Mid trip temp: 195*F

Outside temp: 10*F

Terrain type: mostly flat some hills

If you could use this format it might help keep it clean. Please dont post in town temps as the converter is provably unlocked alot. Coming from my Allison 5spd in my 05 duramax, anytime you were in od the torque converter was locked and temps ran this time of the year on similar trips at about 120*F. That trans has no pressure modulation though (lockup about 140psi and unlocked about 200 something).

Chris · March 3, 2015

Hey guys I was wondering if anyone would post your trans temps and driving atmosphere. It seems like my transmission is running warm to what I would expect.

Mileage on truck: 2200 miles

Trip type: 5hr interstate 70-80mph

Mid trip temp: 195*F

Outside temp: 10*F

Terrain type: mostly flat some hills

If you could use this format it might help keep it clean. Please dont post in town temps as the converter is provably unlocked alot. Coming from my Allison 5spd in my 05 duramax, anytime you were in od the torque converter was locked and temps ran this time of the year on similar trips at about 120*F. That trans has no pressure modulation though (lockup about 140psi and unlocked about 200 something).

195 will be the average. The newer 6 and 8 speeds have a thermostat in the cooling system. GM wants them to run at 195.

Stoddard · March 4, 2015

OK sounds good! Is this thermostat internal to the transmission? It made me nervous, I was thinking maybe the torque converter was slipping or something. I hope it stays cool while pulling this summer.

LongrangeLauber · March 4, 2015

What Chris said. I've towed 5500 pounds and it hasn't gone much over 200 degrees and I'm not light on the throttle either. You'll be fine. Kinda stupid IMO but it's to reduce the shift shock. I'd rather have it stay cooler but that's just me

Yes it's internal

CounterMeasure · March 4, 2015

Interesting. I've yet to see my transmission make it over 170 or so. Well, at least the original transmission never did. I'll see what the replacement does tomorrow.

Honestly, if your only worry is transmission temp, consider yourself lucky compared to those of us having them replaced. ;-)

Stoddard · March 4, 2015

Well see that's what worries me. It doesn't seem too bad yet, I've noticed a few weird shifts but my main concern is a intermittent but noticeable harsh 3-1 downshift coming to a stop and lately king of unwinding the rear driveline in a quiet bang...so we shall see. First time I took it in they said its because of my 305/55r20's. "Of course its gunna shift bad it hasnt got the right shift pattern." Please, im not dumb, I used to be a gm tech. I'm just waiting for newer software to come out.

CounterMeasure · March 4, 2015

My replacement transmission is much better behaved than the original one. On the 50 mile drive back from the dealer, I checked the temp and the gauge showed it was just shy of 200F (I have the big LCD DIC, so I get a fake trans temp needle gauge when I hit the tow button, and not the readout as shown in the smaller DICs). That's warmer than I ever saw the original transmission make it up to.

fondupot · March 4, 2015

Yea ~200 seems to be what GM wants these to run at. Like others have said. It's a bit on the warmer side, but still not terrible. Warmer fluids means the the trans can work easier, which results in better mileage. That's what GM is going for.

redwngr · March 13, 2015

Mine runs much cooler.

40F ambient and an hour+ of running a combination of local rural and freeway and the max temperature was about 175F.

Much warmer than my Allision would have run, but lower than the 200F being reported,

Silverado-Hareek · March 13, 2015

My 2007 4 speed averaged about 175 in the winter and 195-205 in the summer depending on how long or fast I was driving it. My 2014 6 speed is operating in the exact same temperature ranges.