07 Denali Tranmission Temp

chrisnigro · February 23, 2007

I have an 07 Denali XL. Last week I was stuck in some stop and go traffic and noticed my transmission temp go from 146 to 223 Degrees. Being winter in the mid-west it was 10 degrees outside. I also noticed that as the tranny temp went up as I slugged forward, there was quite a bit of banging from the rear end. Not to mention it would shift hard from 1st to 2nd.

I have the Trailer package so, I assume I have the transmission cooler. I know that if I am moving slowly, no air gets to that cooler and the tranny temp will rise.

My question(s); what is the hottest the transmission can get before damage occurs? Is this banging normal?

bobcat5544 · February 23, 2007

You should not be at 223 deg in cold weather. Most likely the trans may need an update or the one of the solenoids/valves in the valve body are sticking causing a clutches not to be fully applied so it slips and heats up the trans fluid.

KB06YUKONXL · February 24, 2007

If you are sitting in traffic it will heat up to 200 in about 30 minutes of stop n go. My 06 does the same thing. Make sure your trans fluid is full. You have synthetic DexronVI in that trans. It can take a lot of heat but the 6 speed transmissions in the GMT900's run hotter that their 4 speed predecessors. Nature of the beast. The clunking in the back? Have your slip yoke checked by your dealer. It may be sticking and need some grease.

C & A s Dad · February 25, 2007

The banging is not normal and you need to get this checked.

If you have the tow package the cooler is mounted right in the middle of the grille. If it is there you will see a 5" x 11" cooler just behind the GMC in the grill. 223 seems to hot to me with outside temps at 10 degrees. I updated my cooler on my 02 model with a stacked plate cooler about twice as big as the OE unit and I am getting 120 degrees or so in 60 degree weather.

With all that said, 223 is not too hot and will not "hurt" anything but I would like to see it running cooler than this. Your warning light likely comes on at 250.

Check to see if the cooler is there and let us know.