2008 Denali XL

[Coyneman1]

I have a 2008 GMC Denali XL Full Time AWD. I am concerned about the transmission temperature when towing as well as the expected mileage.

I am not shocked that the mileage is low - about 9.5MPG when towing - but the Transmission temperature scares me. It fluctuates from 180-210 when towing - and I don't think I have a transmission cooler. Is this temperature range normal?

 

[jimtoo]

Hi Coyneman1,

Welcome to the Heartland Owners Forum. We have a great bunch of people here and all willing to share information.

By not having an external tranny cooler, your fluid will be about same temperature of the coolant in the engine since the only cooler you have in in the radiator. The temps you mention should not be a problem.

Enjoy the forum.

Jim M

 

[thomasinnv]

i would definately get an after market cooler on that tranny. you need to keep that thing cool. start pulling steep hils in summer time and you are going to get a lot hotter than 210.

 

[rumaco]

Transmission temperatures will (should) be ambient plus 100 degrees F (give or take a little). So if it is 50 degrees Farenheit outside the transmission should be somewhere around 150 degrees Farenheit. The size of the cooler and the type of fluid you have, plus what you are pulling will change it some, but this is a great starting point. I have an oversized cooler and run Amzoil synthetic ATF and pulling my BIGHORN through Oregon to Port Angeles Washington and the outside air temp of about 60 degrees F the transmission was about 175 degrees F after climbing the grades and about 10 degrees cooler when going down or level travel (average) according to the guage. Coming up deadmans pass it rose to about 195 degrees (bad grade!!!)

 

[newbie]

My trucks transmission temp when towing in the summer months average around 200. Last summer I pulled a looooooong 9% grade in West Virginia that started as a hair pin turn at almost a dead stop. I was loaded with gear and full water tanks. I went from 208 to 230 and starting getting nervous. This was the last hill we had to climb after two hours of state roads in the National Forest. I never got a warning light but I think that is at the high end of the safe zone. That was also the only time my engine temp move above 210.

John

 

[caissiel]

If you have a GM Gas and transmission, you do have to keep a close eye on the transmission, without an additional cooler its even worst. The engine heating the cooling water in the rad kills the transmission OEM Rad oil cooler. I found by keeping the engine reved up to max. torque RPM of 3000, everything works much better. A meet a lot of people trying to save fuel by using a lower RPM, Its a fact that for a gas engine pulling, its much better using the Max Torque RPM. Same as diesels but at lower RPM of 1800 to 2100 RPM.