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Open Roads Forum  >  Tow Vehicles

 > GM Yukon XL Denali Transmission Temps

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hawkeye-08

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Posted: 06/17/19 04:04pm Link  |  Quote  |  Print  |  Notify Moderator

We had a 2008 GMC Yukon XL Denali, it did get warm towing the 7k travel trailer. Once the transmission gets up to engine temp, they both climb together. We posted on this forum back then and one of the members had emailed factory and gotten a response.

My own research agrees. We traded to 2011 GMC 2500HD and heavier trailer, but if we were keeping the Denali, I was going to put after market trans cooler on.

This is the response they got.

I was also concerned at one pointhowever and contacted GM with the question. There answer was: Good Morning! Thank you for giving me the time to do some research on your concern with the transmission temperature. I have consulted one of our dealers and am happy to inform you that I have the information you’ve requested. The normal operating temperature is between 160°F to 200°F (71°C to 93°C). For towing, the normal operating temperature is between 235°F (113°C) to 260°F (127°C).

dodge guy

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Posted: 06/17/19 04:15pm Link  |  Quote  |  Print  |  Notify Moderator

Not bad, but I also would install an extra, larger cooler.


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hawkeye-08

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Posted: 06/17/19 04:40pm Link  |  Quote  |  Print  |  Notify Moderator

marcsbigfoot20b27 wrote:

Tru-cool 40K. Google or amazon it.


I plan on getting this one for my 2011 GMC Sierra 2500HD (thermal bypass model).

time2roll

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Posted: 06/17/19 04:49pm Link  |  Quote  |  Print  |  Notify Moderator

I would be changing the transmission fluid to synthetic if not already done.
Next I would be checking that radiator if it was the largest available.
Maybe change out the fan clutch.
Lastly I would install the extra capacity transmission cooler.


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Campfire Time

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Posted: 06/18/19 07:19am Link  |  Quote  |  Print  |  Notify Moderator

I have a couple of questions, are these temps sustained, that is for hours on end, or just at the times climbing the grades? Are you using any kind of custom grill shell or grill replacement?

If these are not sustained temps it will not hurt a thing. Thinking that it is comes from using the old Dex III fluid. Your truck has Dex VI which can withstand higher temps for short bursts far better than Dex III could.

If you are using a grill shell or grill replacement it could be impeding the air flow.

time2roll wrote:

I would be changing the transmission fluid to synthetic if not already done.


Al GMs from 2006 and up use Dex VI, a synthetic blend.

time2roll wrote:


Next I would be checking that radiator if it was the largest available.


It is since is already has the auxiliary cooler

time2roll wrote:


Maybe change out the fan clutch.


It has electric fans

time2roll wrote:


Lastly I would install the extra capacity transmission cooler.


I agree, with that kind of weight and towing in mountains, it would not hurt.


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Bionic Man

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Posted: 06/18/19 07:54am Link  |  Quote  |  Print  |  Notify Moderator

@Chuck D, the Yukon runs 220* (or so) on flat ground towing. It is going up passes that it runs higher, and it takes more time to cool down after cresting the pass than I would expect - so maybe 10 minutes above 240*, and a couple minutes above 250*? Those are estimates as I didn't think to time it.

I do not have any obstructions in front of the grill.

@Hawkeye, wow, I really didn't expect that to be normal operating temps per GM. But that does pretty much go with what I have had two dealers tell me.

The truck does get hot enough that the outside temperature gauge is pretty much worthless anytime I am towing (displays around 10* above ambient temp), and the floor of the Yukon gets hot enough to make the dogs uncomfortable/too hot laying on the ground.

I will look into that Tru-Cool.


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Posted: 06/18/19 06:26pm Link  |  Quote  |  Print  |  Notify Moderator

That’s extremely high!!! Fluid needs to be changed way more often at those temps.

33k combined from 6-12% grades with temps in the high 80’s to 100 the trans is never over the mid 170’s.


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bartlettj

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Posted: 06/19/19 09:01am Link  |  Quote  |  Print  |  Notify Moderator

Since the engine and transmission cooler share space, keeping the engine cooler helps too. Higher revs are actually better for this, so let it shift and rev if it needs to. Make sure the thermostat, radiator cap, and coolant are in good shape, as well as the ignition system.

Bionic Man

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Posted: 06/20/19 09:06am Link  |  Quote  |  Print  |  Notify Moderator

Just ordered the Tru Cool 40k with the thermal bypass.

Thanks for the advice. Will report back after installation and a test run.

parker.rowe

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Posted: 06/20/19 01:38pm Link  |  Quote  |  Print  |  Notify Moderator

bartlettj wrote:

Since the engine and transmission cooler share space, keeping the engine cooler helps too. Higher revs are actually better for this, so let it shift and rev if it needs to. Make sure the thermostat, radiator cap, and coolant are in good shape, as well as the ignition system.


This. From the factory the run the trans fluid through the radiator cooler first, then the external cooler.

My trans temp, as per a scan tool, usually matches the engine temp pretty closely when climbing hills...AS LONG AS the torque converter is locked.

Once the converter unlocks the trans temp can start creeping up.

Your truck is already running at 220 normally, so if it is getting warmer than that pulling those killer hills you have our there, it is not a stretch to think it would hit 250-260. I feel like that is high, but I'm not an engineer that designed the thing. [emoticon]

My truck runs around 180-185, sometimes slightly warmer pulling hills. Rarely hits 200. But this is because I have a 175 thermostat in it rather than the factory 195.

I think the ECU intervenes at 270 trans temps and gets more aggressive with torque converter lockup.

Make sure you don't have a bunch of leaves and bug buildup in the cooling stack. I found a whole bucket of leaves between the AC condenser and the radiator when I had to replace the radiator a few years ago. Cleaning that out helped me a lot.


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