Transmission not getting to temp when cold out.

[JTdiRtyD]

I'm having troubles with my transmission oil not getting to temp when it's cold out. I can let the truck get to operating temp, and then drive 30+ miles and I still wont see over 140deg transmission temps. I believe this is causing the transmission to want to stay in 7th and tank fuel economy.

I thought these were thermostatically controlled and shouldn't push oil through the cooler until it reaches temp, correct? If so, what temp should it be opening at? Is there a lockout where it might be stuck open (my Tacoma had a lockout for fluid changes and level checks)?

If the tstat is operating fine, which I find hard to believe, I might need to look into a partial cooler block.

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[Rusty PW]

Believe they removed the tstat. But can't remember which year.

 

[Maximus Gladius]

Can’t remember if my 3rd transmission had the thermostat removed but the 4th one certainly was sometime in 2023 when it was replaced.
OP, how many miles you put on and what year model you have?You say your milage is in the tank. How bad is it? Milage dropping can be a cause of one bad thing or a myriad of small things but with a diesel, nothing is small. Does diesel change for the winter like gas does? I’ve seen my gas milage drop by 2 mpg in the winter.

30 miles,… I wouldn’t see temps any hotter than yours.

 

[Stan H]

Believe they removed the tstat. But can't remember which year.

Yes believe it was 22 or 23 . I read it somewhere . Mine will do the same thing. I can run for 65 miles in the cold and transmission get only up to 172degrees. At 30 miles mine will still be in the 140's . Sounds normal to me . And I would be delighted if mine ran in the 140 to 170's year around.

Oh and yes now I am running a 2024 model transmission.

 

[JTdiRtyD]

Can’t remember if my 3rd transmission had the thermostat removed but the 4th one certainly was sometime in 2023 when it was replaced.
OP, how many miles you put on and what year model you have?You say your milage is in the tank. How bad is it? Milage dropping can be a cause of one bad thing or a myriad of small things but with a diesel, nothing is small. Does diesel change for the winter like gas does? I’ve seen my gas milage drop by 2 mpg in the winter.

30 miles,… I wouldn’t see temps any hotter than yours.

Well this morning it was -9 and my trans temp never got above 140deg, and I saw around 14mpg when checking on the highway. This afternoon it was about +5deg and trans temp got up to 160 (after a lot more driving around post before heading home) and my mpgs went from 14 when it read 125ish, to 18 after my trans temp reached 162. I normally see around 20mpg. Trans fluid is meant for 160-200 operating temp for best performance and efficiency, so my only guess is the colder trans oil temps are degrading efficiency.

I've owned diesels for years, so I'm familiar with how economy changes with winter blends, longer idles, etc., but this is a significant drop. I'm going to block off some of the cooler and see if mpgs consistently increase with warmer trans temps, and I'll report back.

 

[ShadowsPapa]

Yes believe it was 22 or 23 . I read it somewhere . Mine will do the same thing. I can run for 65 miles in the cold and transmission get only up to 172degrees. At 30 miles mine will still be in the 140's . Sounds normal to me . And I would be delighted if mine ran in the 140 to 170's year around.

Oh and yes now I am running a 2024 model transmission.

When it's cold mine doesn't get warm fast at all and doesn't really get all that warm even after a lot of driving around.

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