GM - LV HP ATF, Ideal Temperature?

[AdmiralYoda]

A little backstory...I have a 2021 GMC Canyon with the 8L45 transmission. Supposedly it got the updated Mobil 1 HP LV ATF from the factory. I've replaced it every 25k just for preventive maintenance. GM says that 95-203F is the operating range for my transmission. Fine with that.

My 8L45, like many full-size truck 8L90 counterparts does not have a bypass thermostat for the fluid. This means 100% of the fluid goes to the radiator and then to the external transmission cooler. In the summer my transmission usually tops out at 120F and maybe 135F in traffic when its hot out. In the winter I'm lucky to ever see above 90F.

So what's the problem? Clearly I'm not overheating my transmission but I've always wondered what the ideal temperature for transmission fluid is. Does the additive package perform best at a certain temperature? Does the lubricity perform better at a certain temp? At what temp does the moisture that may accumulate in the transmission burn off?

I've always felt that warm-hot oil (engine or trans) is better than cold oil. Any thoughts here? Does ATF like to be at an ideal range of temperatures for improved performance and longevity? Thanks!

 

[buster]

I have a 22 Colorado. Same unit. I see ATF temps from 90-150F. I'll hit 140F's if off-roading and going slow.

I don't know what the ideal temperature is, but the fluid should easily handle the 90-150F temps we see. What was more of a concern with this unit and fluid was the original fluid was hygroscopic.

 

[MrHorspwer]

It's not too warm; It's too cool.

Part of the issue (not all of it though) with the original Dexron HP in the 8Lxx transmissions was it was incredibly sensitive to moisture in the fluid. Without the thermal bypass, ATF remains cool, condensation in the fluid is never fully evaporated, and the friction characteristics of the fluid degraded. That's why a fluid flush typically solved the issue.

The LV ATF HP fluid has a more robust additive package that doesn't degrade so much with condensation present and solves it from the point of view of the fluid. The addition of the thermostatic bypass valve was the second piece of the puzzle and the 8Lxx bypass has a really high temperature threshold before it sends fluid to the cooler: 194F. This is versus 160F for 6Lxx transmissions and Dexron VI.

If you dig into GM's diagnostic information and look into torque convertor diagnosis, there is a series of steps called Transmission Condensation Reduction that instructs brake torquing the vehicle until transmission fluid temp is 230F, then driving normally until temps return to less than 194F. This was to evaporate any condensation in the fluid.

 

[Brian123]

A little backstory...I have a 2021 GMC Canyon with the 8L45 transmission. Supposedly it got the updated Mobil 1 HP LV ATF from the factory. I've replaced it every 25k just for preventive maintenance. GM says that 95-203F is the operating range for my transmission. Fine with that.

My 8L45, like many full-size truck 8L90 counterparts does not have a bypass thermostat for the fluid. This means 100% of the fluid goes to the radiator and then to the external transmission cooler. In the summer my transmission usually tops out at 120F and maybe 135F in traffic when its hot out. In the winter I'm lucky to ever see above 90F.

So what's the problem? Clearly I'm not overheating my transmission but I've always wondered what the ideal temperature for transmission fluid is. Does the additive package perform best at a certain temperature? Does the lubricity perform better at a certain temp? At what temp does the moisture that may accumulate in the transmission burn off?

I've always felt that warm-hot oil (engine or trans) is better than cold oil. Any thoughts here? Does ATF like to be at an ideal range of temperatures for improved performance and longevity? Thanks!

Where are you taking this Trans Temp, is this on the Dash? Here is what you do, in the Summer after a long drive, when you get home aim an infrared gun at the trans pan, same thing for the winter.

Your External Transmission Cooler has a bypass in it, here is how it works, when the trans fluid is cold, cooler, or thicker, the fluid bypasses your External Trans Cooler. The External Trans Cooler you have is like the stacked plate B&M external trans cooler, you do not have a tube and fin trans cooler that was offered back in the 1980's.

Another thing for you to realize is that you are running LV Fluid which is probably like the Dexron VI fluid and it is thinner than the old stuff like Dexron III

You are fine with the Temps of the Trans on this Vehicle.

 

[AdmiralYoda]

Thanks guys! To be clear I'm not concerned that the low-ish transmission fluid temperatures are harmful to the transmission, I'm more concerned that the fluid itself will not be operating at ideal temperatures. Water not being able to burn off is one concern.

If an engine had an oil cooler that somehow was keeping the engine oil at +20F above ambient temperatures we might be concerned, no? Generally we like the engine oil to be hot, but not too hot.

And yes, I did use a laser gun pointed at my transmission pan. It read within 10-15 degrees of the trucks displayed temperature output (and my OBDII scanner). My transmission operates at about 20-30 degrees above ambient in typical conditions.