Trans temp confusion

[jetfixer320]

I have a 2025 Yukon AT4 Ultimate on order. It should be here by the end of July. (LZ0 power) But I'm confused.
I have no intention of towing, but on one hand I see people installing things like the PPE Trans bypass valve to drastically lower temps (150F give, or take) BUT,
on the other hand, I see other folks saying 180-200 trans temp is normal.

Should I consider something to lower transmission temperature, or just let it do its thing?

 

[blanchard7684]

To make it more confusing, it seems like the max trailer tow package in the gas engines keeps the trans temps ice cold. On my 24 with 5.3 I rarely go above 170F. This is a Suburban.

 

[Stbentoak]

Unless you are pulling a plow with it, just drive it and don't worry about stuff like this. The vehicle as designed with max tow, can handle the very vast majority of towing duties the way it is.

 

[2024 White Tahoe]

I have a 2025 Yukon AT4 Ultimate on order. It should be here by the end of July. (LZ0 power) But I'm confused.
I have no intention of towing, but on one hand I see people installing things like the PPE Trans bypass valve to drastically lower temps (150F give, or take) BUT,
on the other hand, I see other folks saying 180-200 trans temp is normal.

Should I consider something to lower transmission temperature, or just let it do its thing?

There are people that modify their vehicle and have no idea what they’re doing. They do more damage than good, and can void their vehicle warranty.

Leave the vehicle as designed - GM engineers work very hard to determine the operating characteristics and requirements for their vehicles (poor quality and manufacturing notwithstanding).

 

[viven44]

Our 2024 has no special towing package and I have once towed ~8000 lbs... it was a 4-hour tow. The trans fluid temp was ~180F the entire time.

There are vehicles like my old trucks where the transmission cooler is built into the radiator and thus most of the time it was running the same temp as coolant (~195F !!) with / without towing.

If you are not towing, you have nothing to worry about.... maybe that valve body that people are worried about.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum. You are good to go as is.

 

[jfoj]

Seems by reports for some reason the 6 cylinder Duramax trans temps are running higher than the gas engine transmissions.

Seeing a lot of reports that the Duramax trans temps when not towing are in the 200F range. My Yukon Denali XL with the 6.2l typically has a trans temp around 145-150F the majority of the time when cruising and not heavily loaded or towing. I have seen trans temps jump as high as 160F-165F after a long cruise and hitting stop and go traffic on the highway.

With the ULV (Ultra Low Viscosity) transmission fluid, seems the higher the temperature, the easier the fluid leaks occur in the valve body and cause rear wheel lock up or other shifting problems. The higher the fluid temp, the thinner the fluid becomes and it leaks past poor internal seals and spool valves much easier. This is why the Diesels were some of the first to have the rear wheel lock up transmission recalls.

I am getting ready to rework the valve body in my 2024 Yukon XL 6.2l gas and install a PPE larger capacity oil pan (extra 2.5 quarts) and will likely bypass the valve body internal temperature thermostat so I will see what happens with the trans temps shortly after the rework. I am performing the valve body update as a proactive/pre-emptive/preventative measure, because IMHO it is not IF, but WHEN these valve bodies cause problems. If you wait on a valve body upgrade, you may do premature damage to clutches and the torque converter, so why not address the problem before it occurs.

 

[Scarey]

Running around town today, no towing, baby max, air temp 62f, tranni was around 200.

 

[jfoj]

Read the info about TBV temps toward the end of this bulletin in the link - https://www.tahoeyukonforum.com/thr...n-10-speed-valve-body-kit.153898/post-1975722

Apparently the Duramax have an external, frame mounted Thermal Bypass Valve with a temp setting of 194F (90C). So this is why the Diesel transmission temps are higher. Not sure why GM did this. The gasoline speced transmissions have an internal valve body mounted Thermal Bypass Valve with a temp setting of 143F (61C). This is why I typically see my transmission temp around 145F unless the ambient temps are above 80F and/or I end up in a lot of stop and go traffic after cruising on the highway for long periods.

 

[BacDoc]

There are people that modify their vehicle and have no idea what they’re doing. They do more damage than good, and can void their vehicle warranty.

Leave the vehicle as designed - GM engineers work very hard to determine the operating characteristics and requirements for their vehicles (poor quality and manufacturing notwithstanding).

I agree with you on this but the last part you put in parentheses kinda contradicts everything else that you said?

 

[2024 White Tahoe]

I agree with you on this but the last part you put in parentheses kinda contradicts everything else that you said?

What I was trying to say in a short post was that the intended product can be perfectly designed for use and operation, but if the worker(s) making the product parts and/or assembling it do not do their work correctly, the end result is a poor product.

 

[Stbentoak]

Unless you were pushing 240 or 250 on transmission temp, you have nothing to worry about. 200 degrees plus or minus on a Duramax transmission is considered normal.

 

[JKeller]

For what it's worth, I have a stock 2021 HC with the 6.2L and regularly tow a 4,000lbs trailer with a lot of wind resistance at 75mph. I tow in 8th gear to keep my RPMs at or above 2k rpms at those speeds. My transmission temps have never exceeded 165* even while towing and I have over 105k miles now. I just change the fluid at or before the recommended interval. I agree with what others have said: no need to fix something that's not broke.

 

[blanchard7684]

For reference the 2019-2021 Tundras had no transmission cooler. None. No special boutique fluid either. Folks were driving around with no load hitting 240-245F pan temps in 100F ambient.

The alarm light was set to 302F for transmission temp.

 

[jfoj]

Would be interesting to know the reason the difference between the Diesel and Gas transmission operating temperatures and Thermal Bypass Valve placement.

While 200F may not be such a problem, I assume the Diesel transmission temps will operate higher than 200F depending on ambient temps, traffic and load conditions.

I expect the use of the Thermal Bypass Valve is to warm the transmission fluid up faster to help with fuel economy, they effectively keep fluid from entering the external transmission cooling circuit. Think of it as a engine coolant thermostat that will not allow coolant to flow to the radiator to allow for faster engine warm up. As the automatic transmission is concerned, I assume the Thermal Bypass Valve purpose along with the ULV transmission fluid it to reduce parasitic drag to improve fuel economy and along with the TCM probably makes minor adjustments to shifting again to help with fuel economy and also shift quality feel.

Do not know the exact behavior of the newer ULV automatic transmission fluid, as a general rule the higher the operating temperature and/or the higher the temperature spikes even for a short period can have a dramatic impact on the fluid and additive lifespan. The higher the fluid temperature, the shorter the fluid lifespan and the more frequently fluid services need to be performed. While some may think fluid temps around 200F are problematic, this is not really the case, but personally I would prefer the transmission fluid temp to never exceed 225F for the long term fluid reliability. In general I would personally recommend that you change your transmission fluid every 20-25k miles if you want the best lifespan from your transmission.


See this info for reference:

Transmission Fluid Lifespan Info

 

[StephenPT]

Would be interesting to know the reason the difference between the Diesel and Gas transmission operating temperatures and Thermal Bypass Valve placement.

While 200F may not be such a problem, I assume the Diesel transmission temps will operate higher than 200F depending on ambient temps, traffic and load conditions.

I expect the use of the Thermal Bypass Valve is to warm the transmission fluid up faster to help with fuel economy, they effectively keep fluid from entering the external transmission cooling circuit. Think of it as a engine coolant thermostat that will not allow coolant to flow to the radiator to allow for faster engine warm up. As the automatic transmission is concerned, I assume the Thermal Bypass Valve purpose along with the ULV transmission fluid it to reduce parasitic drag to improve fuel economy and along with the TCM probably makes minor adjustments to shifting again to help with fuel economy and also shift quality feel.

Do not know the exact behavior of the newer ULV automatic transmission fluid, as a general rule the higher the operating temperature and/or the higher the temperature spikes even for a short period can have a dramatic impact on the fluid and additive lifespan. The higher the fluid temperature, the shorter the fluid lifespan and the more frequently fluid services need to be performed. While some may think fluid temps around 200F are problematic, this is not really the case, but personally I would prefer the transmission fluid temp to never exceed 225F for the long term fluid reliability. In general I would personally recommend that you change your transmission fluid every 20-25k miles if you want the best lifespan from your transmission.


See this info for reference:

Transmission Fluid Lifespan Info

View attachment 458938

I don't know the answer to the gas versus diesel transmission operating temperature, but my guess is that the gas engine runs the transmission cooler because there will be more TC slip and unlock events, therefore there needs to be more head room for temperature spikes in certain operating conditions. The diesel has such strong low end torque that there is minimal TC slip and unlock events, so GM can run it at the more "peak efficiency fluid temp."

 

[viven44]

I don't know the answer to the gas versus diesel transmission operating temperature, but my guess is that the gas engine runs the transmission cooler because there will be more TC slip and unlock events, therefore there needs to be more head room for temperature spikes in certain operating conditions. The diesel has such strong low end torque that there is minimal TC slip and unlock events, so GM can run it at the more "peak efficiency fluid temp."

Thats a very good point regarding operating RPMs. The torque converters are likely different as well with different stall speeds. With a lower stall speed there is less slippage. If there is less slippage there is less heat generated....

If the Gas engines were designed to make peak torque closer to 2000 RPM, they would actually get better fuel economy, could perhaps run the same setup as diesel... oh but wait that affects the horsepower number which is all the consumers look at.

 

[jfoj]

Curious what the typical Diesel engine RPM is on the highway. The 6.2 is pretty much 1,500 to 1700 RPM cruising on the highway as long as you're not above that 75 mph.

 

[viven44]

Here is the torque chart including the 3.0L. Quite impressive at 1500 RPM.
Makes 170ft lbs more than the 5.3L, and about 100 ft lbs more than the 6.2L/6.6L!
Only the old school 8.1L gets close.

 

[StephenPT]

Curious what the typical Diesel engine RPM is on the highway. The 6.2 is pretty much 1,500 to 1700 RPM cruising on the highway as long as you're not above that 75 mph.

I don't think there's any gearing difference in the 10L80 gas vs. diesel. They all run 3.23 rear ends so cruising RPM will be the same regardless. I have 18" wheels, but I believe GM keeps the rolling diameter the same for the 18, 20 and 22" wheels. IIRC mine is at 1500rpm at 70mph.

When the LM2 came out they showed in the marketing debut that it makes 80% of peak torque at 1250rpm and hits peak torque at 1500rpm. Watching the gear indicator on my Banks IDash I'm usually up into 9th gear by about 45mph. It goes to 10th gear at ~55mph. What's great about the diesel is cruising the highway at ~65mph, the transmission never leaves 10th gear unless it hits a significant grade.