Transmission Temperature Hitting 220s

[DustMcGrath]

First of all sorry, I know there are a ton of transmission temperature threads...

 

My truck is a 2025 LZ0 High (10l89 10-speed) High Country with NHT max trailering package. The NHT package is supposed to have "enhanced cooling."

 

Normally the trans temp sits around 200. It seems like with any real stress it quickly jumps into the 220s (for example climbing a grade unloaded at lower speeds). I haven't towed much with this truck, but I'm concerned if it gets this hot unloaded. 

 

I've tried a few different things to keep the temps down (tow/haul mode, sport mode, low range when that makes sense) and nothing seems to affect it. 

 

I'm curious if others are the same behavior or if anyone has found techniques to keep the temps down. It seems like it just can't handle reduced airflow at lower speeds, even with relatively light loading. 

 

Thanks!

 

 

 

[diyer2]

Switch a a 100% synthetic trans fluid, Amsoil works for me.

[newdude]

2 hours ago, DustMcGrath said:

First of all sorry, I know there are a ton of transmission temperature threads...

 

My truck is a 2025 LZ0 High (10l89 10-speed) High Country with NHT max trailering package. The NHT package is supposed to have "enhanced cooling."

 

Normally the trans temp sits around 200. It seems like with any real stress it quickly jumps into the 220s (for example climbing a grade unloaded at lower speeds). I haven't towed much with this truck, but I'm concerned if it gets this hot unloaded. 

 

I've tried a few different things to keep the temps down (tow/haul mode, sport mode, low range when that makes sense) and nothing seems to affect it. 

 

I'm curious if others are the same behavior or if anyone has found techniques to keep the temps down. It seems like it just can't handle reduced airflow at lower speeds, even with relatively light loading. 

 

Thanks!

 

 

 

 

 

It is working as designed.  NHT and non NHT trucks have the same exact transmission cooling setup.  NHT just gets a larger radiator.  

 

The transmission cooler loop on these is as follows.  

 

-Transmission out goes into an oil to water heat exchanger (item #1 in the first illustration below).  This exchanger has engine coolant opposite the transmission fluid and uses engine coolant to warm and then regulate the transmission fluid temperature when its in the operating window.

 

- From the cooler it goes to a thermal bypass valve (item #11 in the 2nd illustration below).  If the ATF has not reached the temp to open the bypass (194F), it loops back.

 

- When it reaches 194F, the thermostat opens and ATF then flows out to the oil to air auxiliary cooler (item #17 in the 2nd illustration) at the front of the truck.  From there it goes back to the transmission.  

 

Your only fix would be to swap for the PPE thermal bypass delete block which will open the loop to the aux cooler all the time.  It will STILL run warm, probably 170-200F, but that's as low as you'll get it as its still flowing through the oil to water exchanger.  

 

 

[DustMcGrath]

@newdude great info, thank you!

 

So opening the thermal bypass valve early (or all the time) would cause temperature to rise more slowly, but above 194F there would be no difference from normal operation?

 

It seems like the only practical ways to bring down the peak temperature would be to improve the oil-air heat exchanger in some way or increase fluid capacity?

[newdude]

1 hour ago, DustMcGrath said:

@newdude great info, thank you!

 

So opening the thermal bypass valve early (or all the time) would cause temperature to rise more slowly, but above 194F there would be no difference from normal operation?

 

It seems like the only practical ways to bring down the peak temperature would be to improve the oil-air heat exchanger in some way or increase fluid capacity?

 

 

Rise more slowly?  Debatable.  It would run slightly cooler, yes if anything after adding the thermostat delete kit from PPE.

 

PPE makes a larger front aux cooler which they "claim" will lower temps 45 degrees but I have not used it.  

 

IMO, especially in cold states, I would not want to mess with the first cooler, the oil to water one.  Cold states, you want heat in the transmission for it to shift properly, and you don't want moisture in the ATF. 

 

Ideal temps for automatic transmissions to do their job the best is 175-220F.  Hotter than 220F you start heading towards fluid degradation and shortened fluid life/service intervals.  240F can start varnishing things like the fluid, clutches, etc.   

[PunchT37]

2 minutes ago, newdude said:

 

 

 

 

 

Ideal temps for automatic transmissions to do their job the best is 175-220F.  Hotter than 220F you start heading towards fluid degradation and shortened fluid life/service intervals.  240F can start varnishing things like the fluid, clutches, etc.   

Why do they have the gas 10l80 opening at 145?

[newdude]

7 hours ago, PunchT37 said:

Why do they have the gas 10l80 opening at 145?

 

 

No.  Idea.  

 

That's just where GM set it to.  Why?   

 

 

[PunchT37]

2 hours ago, newdude said:

 

 

No.  Idea.  

 

That's just where GM set it to.  Why?   

 

 

Good question. Most to all of what I hear in internet land is to have 212 trans temp to boil off the water.

 

That`s where my earlier comment was coming from.