Transmission temperature 10speed with 3.0 LZO Duramax

[newdude]

1 hour ago, redwngr said:

Thanks for the correction! 

 

Is there an Allison fluid that is also recommended? 

 

 

 

No because the "Allison" 10 speed is not an Allison.  Its a GM transmission with Allison's name on it.

[Rick_]

6 hours ago, Grumpy Bear said:

 

I see we are neighbors. Good, then we have some common experience. How does the truck run on a -20 F winter day first start of the morning? Does is hang on to the 1-2 shift or the 2-3 a bit longer than when hot? Too cool. Then there are perhaps some parameters within the TCM or ECM that require a certain temperature to satisfy some requirement or another. Too cool. 

 

Now I don't own an Allison 10 so don't know it's programing but I'd still wager that the temperature in which ALL requirements are satisfied for 'normal' operation is something like 105-115 F AFT temperature. My 6L80E is 107 F. 

 

Anything between that trigger number and 'too hot' is a sound operating temperature. Too hot is over 175 F and will be for every transmission that uses hydrocarbon lubrication. So 120 F to 175 F is target. (120 F to 160 F for older boxes still using full conventional fluids). 

 

That doesn't mean the OEM designed it to operate in that area. Wear is not their first priority. Fuel economy and cost take priority over wear as long as wear keeps them out of the warranty claim box and they don't mind loosing a certain percentage of them even to that. Bean counters are not engineers and even engineers are subject to bosses whose priorities are not the consumer they sell to but the shareholders they placate. 

 

Anyone that tells you that 120 F is too cool and will accelerate wear is full of Internet regurgitated . Anyone that tells you that running over 175 F continuous will not shorten the life of the fluid/gearbox, ditto. 

 

There isn't any Kryptonite seals or clutch bonding materials saved only for Allison and no Unobtainium fluid that will take the heat of the sun. 

 

Does this mean that a box running 215/225 F is doomed? Not necessarily. It means the owner/operator will need to be more diligent about fluid exchange and live with less cushion for that long grade or silly hot day. 

 

 

Transmission life follows fluid life and the fluid doesn't know or care what box it is in.

 

 

This information originally came from Kendal Oil and has been displayed two dozen different ways by every Internet concern there is; often corrupted to read transmission life and not fluid life. 

 

You may notice that the OEM temperature range and the fluid change intervals come pretty darn close to the chart. You will also notice that when they don't the warranty miles isn't all that. There is no 'forever fluid'. 

 

Do with this information as you please. It will have no effect on my equipment whatsoever.    

Here's some info from nextgendiesel on how to extend transmission life.  Nextgen also sells valve body repair kits directly to GM dealers now to fix the issues the 10spd transmissions are currently having.

https://nextgendiesel.com/blogs/transmissions-101/top-5-ways-to-extend-the-life-of-a-factory-transmission

For temps over 200F, the seals and o-rings need to be made out of a more expensive HNBR rather than cheap nitrile.  Also, planetaries and shaft/bushing interfaces like a bit more lubricity than what LV and ULV fluids afford.  Taking the word of a dealer is not a be-all end-all answer as I've had dealers and sales managers lie to me face to face.  My experience with automatic transmissions and heavy duty hydraulics is that a temperature limit below 105C makes for happy customers.  YMMV

[redwngr]

6 hours ago, newdude said:

 

 

No because the "Allison" 10 speed is not an Allison.  Its a GM transmission with Allison's name on it.

Yes, the never ending is it a GM or an Allison argument that doesn't matter anyway. 

 

When the 5/6 speed was designed and approved, Allison was a GM division -- so I guess it's a GM transmission too.

[Atlas]

Sounds like I need to pick me up a thermal bypass and 1-2 quarts of ULV for a quick little project.

 

Is Valvoline ULV acceptable, or do I need to find the AcDelco brand ULV?

Edited August 16, 2025 by Atlas

[Grumpy Bear]

5 hours ago, Rick_ said:

Here's some info from nextgendiesel on how to extend transmission life.  Nextgen also sells valve body repair kits directly to GM dealers now to fix the issues the 10spd transmissions are currently having.

https://nextgendiesel.com/blogs/transmissions-101/top-5-ways-to-extend-the-life-of-a-factory-transmission

For temps over 200F, the seals and o-rings need to be made out of a more expensive HNBR rather than cheap nitrile.  Also, planetaries and shaft/bushing interfaces like a bit more lubricity than what LV and ULV fluids afford.  Taking the word of a dealer is not a be-all end-all answer as I've had dealers and sales managers lie to me face to face.  My experience with automatic transmissions and heavy duty hydraulics is that a temperature limit below 105C makes for happy customers.  YMMV

 

 105C? 221 F? My milage does vary. LOL. I'm happy at 160 F and adding cooling above 175 F sustained. But yea, if you change oil often enough you can get away with murder. I'm just not going to do it. 

[newdude]

20 hours ago, redwngr said:

Yes, the never ending is it a GM or an Allison argument that doesn't matter anyway. 

 

When the 5/6 speed was designed and approved, Allison was a GM division -- so I guess it's a GM transmission too.

 

 

The latter has fact, Allison was a GM owned division from 1929-2007.  The 1000 series came out in 1999 and made it into the GMT-800 HD pickups for the 2001 model year.

 

Your first statement, there really is no argument about it.  Allison themselves in their press release from 2018 clearly stated its just branded Allison.  GM should have pulled their heads out of their a$$es and just have Allison design and engineer a new transmission for the 2020 product launch instead but noooooo gotta do an in house unit instead.  

 

Chevrolet to Offer 10-Speed, Fully Automatic Allison Branded Transmissions in 2020 Silverado Class 2/3 HD Trucks | Allison Transmission

 

“We built the new 2020 Silverado HD with more differentiation than ever before, to meet the needs and priorities of our customers,” said Jaclyn McQuaid, chief engineer, Silverado HD. “By offering the new Allison 10-speed, tested and validated in partnership with Allison Transmission, each transmission will deliver the legendary quality and durability that customers have come to expect.

 

The Allison branded automatic transmission, manufactured by General Motors, combines enhanced performance and fuel economy, greater operational flexibility, and improved driver comfort and control, with an industry-leading reputation for uptime and reliability. Designed for high-performance and low-maintenance, the Allison 10-speed coupled with Chevrolet’s Duramax diesel engines provide the superior power delivery and productivity customers demand."

Edited August 16, 2025 by newdude

[Atlas]

Before I install this thing, a few more questions:

 

Does the 10L80 require a minimum transmission temperature to achieve TC lockup? I remember this from my 2015 6-speed. Would installing a PPE TB prolong the fluid warmup, and extend the time it takes for TC lockup to occur?

 

Does the 10L80 (specifically, for LZ0 diesels) have an ATF heater? If so, does installing the PPE TB cause any heater to continually heat the fluid in attempt to achieve stock run temperatures of ~195F+ ?

[Holy Smokes]

Bringing this topic up again.... 2025 GMC Sierra 1500 with 3.0 & 10L80.  Was seeing temperatures of around 200°F in typical summer conditions.  So, installed the PPE thermal bypass.  Summer driving in the Midwest with ambient temps around 80°F* seeing only ~130°F transmission temps.  So, about 50* delta. 

 

Now that it's winter and the ambient temperature is roughly 30°F, I'm still seeing only a 50°F delta.  Meaning, my trans temp is only around 80-90* tops.  PPE states that I must remove the bypass each winter and then reinstall it in the spring.  Seriously?!?

 

Question... how cool is too cool? 

 

I'm not worried about the potential 0.1 mpg efficiency gain from a higher-temperature transmission, but I AM concerned that at only 80°F, is the transmission being impacted and doing its job properly?  What happens when it's 0* outside?

Edited December 3, 2025 by Holy Smokes

[CamGTP]

My opinion is that sub 100 degrees is too cool. Even on the older 6L80e's before the thermostats were installed I would see 100-115 degrees in the winter, it did take a little while to reach that though. Temps above 100 is fine, if you drive the truck harder, the temps will climb higher slightly but not always doable when you are just bombing down the freeway.

 

At the rate you are now if you were here in Minnesota, we are already seeing temps in the single digits in the morning so you'd be lucky to reach over 80 degrees it seems. Tomorrows low is -8 or so, going to be chilly.

[newdude]

3 hours ago, Holy Smokes said:

Bringing this topic up again.... 2025 GMC Sierra 1500 with 3.0 & 10L80.  Was seeing temperatures of around 200°F in typical summer conditions.  So, installed the PPE thermal bypass.  Summer driving in the Midwest with ambient temps around 80°F* seeing only ~130°F transmission temps.  So, about 50* delta. 

 

Now that it's winter and the ambient temperature is roughly 30°F, I'm still seeing only a 50°F delta.  Meaning, my trans temp is only around 80-90* tops.  PPE states that I must remove the bypass each winter and then reinstall it in the spring.  Seriously?!?

 

Question... how cool is too cool? 

 

I'm not worried about the potential 0.1 mpg efficiency gain from a higher-temperature transmission, but I AM concerned that at only 80°F, is the transmission being impacted and doing its job properly?  What happens when it's 0* outside?

 

 

That is too cool for sure.  Honestly?  Stock is where it should be temp wise, and they usually stay right at that temp anyway year round.  Run a 45,000-50,000mi fluid service interval and it should treat you right.  

 

TCI Auto Transmission Life Expectancy - TCI® Auto

 

"HOW HOT IS TOO HOT?

The ideal operating temperature for automatic transmission fluid is between 175 and 225° F."

 

 

 

Edited December 4, 2025 by newdude

[redwngr]

The 10 speed behind my LZO runs between 190 and 200 winter and summer.

In colder ambients, it takes longer to get there -- but it does. 

 

 

[Rick_]

On 8/14/2025 at 8:09 AM, Rick_ said:

My wife's '22 RST 3.0 with our 5000lb boat running 70mph in rolling hills at around 3000ft in low 90's temp runs up to 201* even with the Max Trailering package.  Looks like it's going to get the PPE bypass.  My '24 3500 Duramax barely cracks 150* with the same boat running between 70-75mph.  

Installed the PPE bypass on the RST last week.  With ambient temps between 75-95, the trans temp dropped from 195-198 unloaded to between 180-185.  Not what I was expecting (also has the Max Trailering package).  I have a Nextgen diesel valve body upgrade kit going in this week and the remaining thermostat in the pressure regulator valve will be removed and I'll see what happens.  
I did the same mod in the Valve body upgrade kit for my '24 3500 HD Duramax and I haven't seen much difference in trans temp but I've just been running back and forth to town so far.  

[newdude]

33 minutes ago, Rick_ said:

Installed the PPE bypass on the RST last week.  With ambient temps between 75-95, the trans temp dropped from 195-198 unloaded to between 180-185.  Not what I was expecting (also has the Max Trailering package).  I have a Nextgen diesel valve body upgrade kit going in this week and the remaining thermostat in the pressure regulator valve will be removed and I'll see what happens.  
I did the same mod in the Valve body upgrade kit for my '24 3500 HD Duramax and I haven't seen much difference in trans temp but I've just been running back and forth to town so far.  

 

LM2 and LZ0 DO NOT have a thermostat in the valve body.

 

LM2 and LZ0 still have the water to oil heat exchanger that the ATF goes through no matter what.  So if the thermal bypass in the lines to the aux cooler is closed, ATF goes out the transmission, into the water to oil exchanger, to the thermostat and then back to the transmission. 

 

When it gets hot enough to open the TBV in the line, it will then flow to the aux cooler out front to regulate temperatures.

 

The cooling system is going to warm the ATF up as the exchanger is part of that entire Active Thermal Management cooling system.  

 

LM2 and LZ0 DO NOT have a thermostat in the valve body.  Just the one in the lines.  Stock TBV opens at 194F.  

 

From TSB 22-NA-182

 

• 10 Speed (10L80, 10L90, 10L1000) - 143F (61C) - TBV is within the valve body on all listed applications except those equipped with 3.0 (LM2) (LZ0) Diesel. The (LM2) and (LZ0) Diesel, the TBV is on the frame rail, external to the transmission and opens at 194F (90C).

 

 

 

As for your big Duramax, the transmission cooler lines still flow through the side tank on the radiator, so deleting the TBV in the valve body will only lower it so much.

Edited July 20 by newdude

[Grumpy Bear]

On 12/3/2025 at 7:01 PM, newdude said:

 

 

That is too cool for sure.  Honestly?  Stock is where it should be temp wise, and they usually stay right at that temp anyway year round.  Run a 45,000-50,000mi fluid service interval and it should treat you right.  

 

TCI Auto Transmission Life Expectancy - TCI® Auto

 

"HOW HOT IS TOO HOT?

The ideal operating temperature for automatic transmission fluid is between 175 and 225° F."

 

 

 

 

Point of clarification on this graph. It is the life of the FLUID not the Transmission being graphed. Compare to his comments below the graph. Get it to the top of the graph and you can kill one in an afternoon. 

[Rick_]

On 7/20/2026 at 3:20 PM, newdude said:

 

LM2 and LZ0 DO NOT have a thermostat in the valve body.

 

LM2 and LZ0 still have the water to oil heat exchanger that the ATF goes through no matter what.  So if the thermal bypass in the lines to the aux cooler is closed, ATF goes out the transmission, into the water to oil exchanger, to the thermostat and then back to the transmission. 

 

When it gets hot enough to open the TBV in the line, it will then flow to the aux cooler out front to regulate temperatures.

 

The cooling system is going to warm the ATF up as the exchanger is part of that entire Active Thermal Management cooling system.  

 

LM2 and LZ0 DO NOT have a thermostat in the valve body.  Just the one in the lines.  Stock TBV opens at 194F.  

 

From TSB 22-NA-182

 

• 10 Speed (10L80, 10L90, 10L1000) - 143F (61C) - TBV is within the valve body on all listed applications except those equipped with 3.0 (LM2) (LZ0) Diesel. The (LM2) and (LZ0) Diesel, the TBV is on the frame rail, external to the transmission and opens at 194F (90C).

 

 

 

As for your big Duramax, the transmission cooler lines still flow through the side tank on the radiator, so deleting the TBV in the valve body will only lower it so much.

So you are saying that there is a water to oil transmission fluid "heater" along with an air to atf heat exchanger?  Where do I get hold of a diagram/microfiche of that routing?   Is the water to oil cooler a bar plate job between the trans thermostat and the air to oil cooler?

In the 2022 10L80/90? valve body there is a valve called the Cooler Thermostat Valve that gets modded to eliminate regulation to the flow to the cooler.  There are two styles - the 2022 has no brass thermostat, but later versions seem to have it.

Testing today after the valve body kit install, zero change in gauge temp unloaded - 180F at 84*F unloaded, so the atf heater is doing its job.   The positive so far is the lag in shifting from R to D has been eliminated.

 

There is a brass "thermostat" in the Cooler Thermostat Valve that is removed with the NextGen kit for the 10L1000 - 135F gauge temp with a 5000lb boat in small rolling hills at 85*F.