For those with the updated tranny thermostat…

dzsmith · March 4, 2023

Had my transmission rebuilt in December 2021. Had to replace my leaking cooler lines recently , and decided to update to the newer thermostatic bypass valve while I was there. The one stamped with 70F and opening at 158f verses 194f on the old one. I’m curious as to what temps you guys are seeing on the new one. On my old one, it would take 30minutes to an hour driving at 70mph to get up to around 194F and it would stay there , as if it may just sorta open and close a little but never really got higher . My new one will get to 158F at around 20 minutes at 70mph, but it does continue to climb. I drove it an hour today . And the highest it got was 171F. I also noticed on the first drive , when I came home, and the vehicle was idling without the fans running , that it climbed to 171 while sitting in the porch. It was relatively cool outside , no a/c running on the vehicle so I’m not surprised my fans were not kicking on and off much , I’m sure I could have idled it long enough too. Anyway , I’m just curious as to what temps Yal are seeing on the new thermostat . It’s obviously opening sooner and keeping the temp out of the 190s but 170s still seems a little high for my liking . It doesn’t stay there , but it does stay in the 160s. Is additional cooling needed ?

CamGTP · March 4, 2023

I don't have the updated thermostat because I just bypass mine but in regards to the fluid temp you are seeing, that is perfectly fine. Optimum fluid life is in that 140-180 degree range.

OffTheAir · March 5, 2023

I got the updated transmission thermostat a couple months ago and I have never seen it go above 170F yet, granted we are still facing the cool winter weather here.

I will say that around this time last year, I was getting in the mid to high 180F range after doing my normal commute. Now I get around 147F to 150F doing the same trip, which is a pretty big difference. Just judging by the behavior of the new thermostat, I would like to bet I will probably see 167-170F at the highest in the coming months or during long trips.

All I will say is, I will gladly take these temperatures any day over consistently reaching 194F and staying there.

dzsmith · March 6, 2023

Yep that’s how I feel. Better than 190. I’ve been commuting in my truck this week. Oddly enough other than the initial 2 drives . It’s never hit 170 again, but we had a little cool front come in so I’m sure that helps. Thanks for the replies. I’m not to worried about it .

newdude · March 6, 2023

On 3/4/2023 at 9:15 AM, dzsmith said:

Had my transmission rebuilt in December 2021. Had to replace my leaking cooler lines recently , and decided to update to the newer thermostatic bypass valve while I was there. The one stamped with 70F and opening at 158f verses 194f on the old one. I’m curious as to what temps you guys are seeing on the new one. On my old one, it would take 30minutes to an hour driving at 70mph to get up to around 194F and it would stay there , as if it may just sorta open and close a little but never really got higher . My new one will get to 158F at around 20 minutes at 70mph, but it does continue to climb. I drove it an hour today . And the highest it got was 171F. I also noticed on the first drive , when I came home, and the vehicle was idling without the fans running , that it climbed to 171 while sitting in the porch. It was relatively cool outside , no a/c running on the vehicle so I’m not surprised my fans were not kicking on and off much , I’m sure I could have idled it long enough too. Anyway , I’m just curious as to what temps Yal are seeing on the new thermostat . It’s obviously opening sooner and keeping the temp out of the 190s but 170s still seems a little high for my liking . It doesn’t stay there , but it does stay in the 160s. Is additional cooling needed ?

2014 truck this sounds normal because the transmission cooler line flow is transmission to the cooler in the radiator, then out to the aux cooler at the condenser then back to the transmission.

Its flowing through the radiator which just happens to be exposed to 210F engine coolant so its providing some degree of warmth to the ATF.

2016-2019 K2 trucks the transmission doesn't go through the radiator at all. Its transmission to the cooler in the condenser then back to the transmission. They run 20-30F cooler so right at the open temp of the thermostat.

steelerdude15 · March 6, 2023

My truck runs between 130F to 151F since I installed the new thermostat. That is a mix of highway, back roads, and city driving.

Edited March 6, 2023 by steelerdude15

Grumpy Bear · March 6, 2023

On 3/4/2023 at 8:15 AM, dzsmith said:

Had my transmission rebuilt in December 2021. Had to replace my leaking cooler lines recently , and decided to update to the newer thermostatic bypass valve while I was there. The one stamped with 70F and opening at 158f verses 194f on the old one. I’m curious as to what temps you guys are seeing on the new one. On my old one, it would take 30minutes to an hour driving at 70mph to get up to around 194F and it would stay there , as if it may just sorta open and close a little but never really got higher . My new one will get to 158F at around 20 minutes at 70mph, but it does continue to climb. I drove it an hour today . And the highest it got was 171F. I also noticed on the first drive , when I came home, and the vehicle was idling without the fans running , that it climbed to 171 while sitting in the porch. It was relatively cool outside , no a/c running on the vehicle so I’m not surprised my fans were not kicking on and off much , I’m sure I could have idled it long enough too. Anyway , I’m just curious as to what temps Yal are seeing on the new thermostat . It’s obviously opening sooner and keeping the temp out of the 190s but 170s still seems a little high for my liking . It doesn’t stay there , but it does stay in the 160s. Is additional cooling needed ?

It's doing fine. It will always run hotter when idling or crawling in city traffic. No air flow, right? As you note, comes back to the 160 F range once moving. Perfect! You can knock that back a bit if you install the cooler water thermostat. If you want to stay below 170 no matter what you will need more cooler with a thermostatic fan that trips 160 F. Improved Racing may be able to help with that.