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Discussion Starter #1
Was driving my 2007 Sierra 1500 classic in the cold spell we have been having and noticed it seemed to be running warm for the weather. Outside temperature was -40 and the transmission was at 150-165 degrees Fahrenheit even driving on the highway. I have noticed run that hot in warmer weather on the highway.

Transmission is a built 4L70e, Yank TT3000 and I have a tru cool 40k routed to go through the factory radiator cooler then the tru cool. I am not running the external thermal bypass.

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You want an auto trans to run 175°F so where its at now isn't bad and wont cause damage.

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Discussion Starter #3
I know the temperature isnt anything to be concerned about.

I'm wondering why in this cold spell we have been having it runs warmer then it would in warmer weather even. I will mention I have been keeping the truck in a heated shop.

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Toxic Masculinity
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Is the converter going into lockup? Yeah when it's +40F it takes half an hour for my temp gauge to budge past 100* using a 40K with the radiator bypassed (no thermal bypass).
 

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Discussion Starter #5
Converter is locked up. My only guess is I know that the box for the transmission cooler advertises the cooler itself having an internal thermal bypass and that may have something to do with it.

I did notice when the truck sat for a few minutes and then I got driving on a highway it did drop the temp rather quickly.

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Toxic Masculinity
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I would panic quite yet. Keep an eye on the gauge and when warm weather rolls in you'll know for sure. If you're close to a regular fluid maintenance change it might be a good idea, and for piece of mind. If you have a Tech2 or HP Tuners (I think) you can monitor TCC On/Off solenoid operation. That stuff is beyond my pay scale... I'm a paint/body guy that turns wrenches.
 

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Discussion Starter #7
I do know when it does get warmer weather wise the transmission does not run this warm. Only happens in extremely cold situations like we are in right now.

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Toxic Masculinity
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I do know when it does get warmer weather wise the transmission does not run this warm. Only happens in extremely cold situations like we are in right now.

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Kinda odd mine is just the opposite in the summer I'm around 160F and the mild winters much lower. Might have something to do with trans fluid viscosity being so heavy in the bitter cold, the fluid has a slower flow in the system. Then after the viscosity lowers through heating it begins to flow normally.
 

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I would guess GM installed a thermal bypass in the radiator itself.

I say that because Iv always bypassed the radiator itself with no thermal bypass like redxray stated, and had the same results.

Running a 4K lockup with the tru cool 40k would take me about a mile or 2 to even shift right in 50 degree weather. Temp gauge would never even reach 100 in AM.
 

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Discussion Starter #10
Well I think I found some explanation as to why this occurs.

I had to go to my brothers place to boost his truck. Had my truck in the shop and gave it a few minutes to warm up. Keep in mind its -40 outside.

Drove there about 20 minutes and the transmission was around 125-130 degrees F. Spent about 10 minutes with the truck idling or at 1500 rpm while we were boosting the truck. Temp went to 150 or so from not moving. Once I left and got on the road the transmission temperature dropped to 110 or 120.

I'm guessing as it was said previously, this cold weather with a big cooler like a tru cool 40k may be keeping some fluid in the cooler too cold.

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Discussion Starter #11
I will also mention I've checked the fluid and it smells and looks clean. Even got a second opinion on the fluid and same opinion.

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