Forum Discussion

Bionic_Man's avatar
Bionic_Man
Explorer
Jun 17, 2019

GM Yukon XL Denali Transmission Temps

My main tow vehicle is my RAM CTD, but when we take the RV as well the truck has to pull my 7000 pound boat. So then we use my 2011 Yukon XL Denali to tow the Malibu.

It has always run hot - both engine and transmission. Especially in the mountains.

Last week we went on vacation. Pulled the boat to Steamboat, Colorado. This was up I70 to Hwy 40 for those familiar with the area. Going up it wasn’t terrible but coming home it was. Up Rabbit Ears pass, I ran it somewhat hard up until about a mile from the top. Engine temp was about 3/4 up the gauge but the transmission temp is what was worse. Even slowing down to run about 4000 RPMs in second, it was 254* at the top.

I ran slower up to the Eisenhower tunnel, but couldn’t keep the tranny below even 240*. Again at the top, it was at 250* - even though I further slowed down. Trying to force it out of 2nd and into 3rd didn’t help (and it was hard to maintain any speed in 3rd).

I’ve? asked two GM dealers as well as an independent transmissio?n shop about it in the past and they told me that is just what to ex?pect towing 7000 pounds with a half ton SUV through the m?ountains and that it would be fine for short periods of time at those temps.

The Yukon does have an auxiliary transmission cooler from the factory.

Is anyone else seeing that high of temps? Is there some sort of idiot light that will come on or will the engine defuel if the temps get too high?
Tow Vehicles
  • Bionic_Man's avatar
    Bionic_Man
    Explorer
    Aug 07, 2019
    Grit dog wrote:
    And for the group, yes it appears GM 1/2 ton trans run hot. By design. Mine and others like it. 2016-2017 models, min 190 when it’s cold out. 200 or close when hot out.
    Seems like it has a 190deg thermostat in it, it’s they consistent.
    If I owned the truck I’d make it run cooler as well.


    It’s not just GM trucks. I’ve been watching the Fords on test drives or rentals as well. 200*-220* is normal.
  • Bionic_Man's avatar
    Bionic_Man
    Explorer
    Aug 07, 2019
    hawkeye-08 wrote:
    Check the coolant level (when cool of course), your engine temp should not behave that way unless something else is going on.. IIRC, you have a 6.2l with plenty of power. Are the fans working ok (I don't recall if you have dual electric fans or a large fan driven by belt). Perhaps water pump needs replacement or fan belt?


    I’ll check coolant when we get home. Fans sound to be working fine and there are no fluid leaks.

    Honestly, if there is a problem, it is likely to be someone else’s.
  • ShinerBock's avatar
    ShinerBock
    Explorer
    Aug 07, 2019
    Grit dog wrote:
    And for the group, yes it appears GM 1/2 ton trans run hot. By design. Mine and others like it. 2016-2017 models, min 190 when it’s cold out. 200 or close when hot out.
    Seems like it has a 190deg thermostat in it, it’s they consistent.
    If I owned the truck I’d make it run cooler as well.


    Or they have their temp sensor closer to the trans fluid going to the cooler instead of the sump like many vehicles. These two places have different temps with the sump being the cooler of the two.
  • hawkeye-08's avatar
    hawkeye-08
    Explorer III
    Aug 07, 2019
    Check the coolant level (when cool of course), your engine temp should not behave that way unless something else is going on.. IIRC, you have a 6.2l with plenty of power. Are the fans working ok (I don't recall if you have dual electric fans or a large fan driven by belt). Perhaps water pump needs replacement or fan belt?
  • Grit_dog's avatar
    Grit_dog
    Navigator
    Aug 07, 2019
    And for the group, yes it appears GM 1/2 ton trans run hot. By design. Mine and others like it. 2016-2017 models, min 190 when it’s cold out. 200 or close when hot out.
    Seems like it has a 190deg thermostat in it, it’s they consistent.
    If I owned the truck I’d make it run cooler as well.
  • Grit_dog's avatar
    Grit_dog
    Navigator
    Aug 07, 2019
    I thought you upgraded the transmission mission cooler to the Expedition model?

    Bummer on the Denali. You can only ask so much out of a vehicle sometimes.
  • wq93's avatar
    wq93
    Explorer
    Aug 07, 2019
    Are you sure that the cooling stack is really clean? Often you get a lot of debris buildup between the condenser and radiator. The HD trucks are well known for this issue after a few years and although you don't have the additional intercooler of the diesel pickups there is still a lot of area between the condenser and the radiator for stuff to get caught greatly reducing airflow.

    It won't make a huge difference, but the engine heat increase may be a little less if the added transmission cooler is plumbed in ahead of the cooler in the radiator tank because it will dump more of the transmission heat before adding it to the engine coolant.
  • Bionic_Man's avatar
    Bionic_Man
    Explorer
    Aug 07, 2019
    Well, today was the day (yesterday now). Loaded everything up to use the Yukon to tow the LSV to Powell.

    Three people and four dogs, and all our gear for 5 days at the lake. Didn’t have much room in the Yukon, put a lot of stuff in the boat.

    Temp was low 90’s when i left home. Temps i have seen before.

    Got on the highway and noticed the engine temperature was running a bit high right out of the gate. Took the first hill by Red Rocks, and it went way high. Couple miles up, and it got bad enough that I shut off the air conditioning. Engine cooled down a little. Inside temp warmed up a bunch.

    Slowed down to about 30 MPH. Turned the air back on, and the engine temp went way up way fast. Before I knew it, there was a message on the dash warning about the temp and that the air was shut off. On the plus side, the transmission temp never got about 200*

    Not a good way to start a 450 mile trip. So we turned around and headed home. Quickly emptied out that Yukon. I hooked the boat up to my truck, my wife took a dog and my nephew in the Jeep, and we left again.

    Set us back by about two hours. But we got here.

    When I had the auxiliary transmission cooler installed, I worried if the added size right in front of my radiator would create another problem. Well, it looks like I have my answer.

    I’m tired of chasing problems with the Yukon. When I get home I will step up my search for a replacement.
  • Bionic_Man's avatar
    Bionic_Man
    Explorer
    Jul 29, 2019
    Towed the boat for the first time since I had the new trans cooler installed.

    Just flat land down I76 and back. Cruise set about 70 MPH, outside temps in the low 90’s, most of the time in 5th gear running about 2400 RPMs, the trans never got above 180*. It spent most of the time in the 160* range. Before the cooler install it ran 200* - 220* on this same trip. Must say so far I am pretty impressed.

    I’ll give it more of a test next week as we will be using it to tow the boat to Utah. The ride home will be the real test - eastbound over Vail Pass and the Eisenhower tunnel is where it would run up to 250*+ before. Will report back again.
  • BurbMan's avatar
    BurbMan
    Explorer II
    Jul 02, 2019
    The trans temp idiot light or warning message is usually set at 275*. 250* is high, but as other said not the end of the world, just put a fluid change on the list at the end of every towing season. Be sure you are using the new Dex VI full synthetic.

    The bigger cooler should help, next step would be an electric fan to flow more air over the cooler.

    ALSO, if your trans is getting that hot you're cooking the rear axle too. I would change the fluid and consider a Mag-Hytec expanded capacity cover, and be sure you have full synthetic in the rear axle also (GM fluid is full syn).

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