2016 Yukon SLT-Hot engine towing up steep 7 mile grade

[Larry Brew]

I recently was pulling my camper up up a 7% grade, 7 miles long and the temp gauge went up to the last mark before hitting 260 red mark. I estimate the temp gauge was at 245-250. No engine overheating warning messages came on dash. I was doing around 40-45 MPH. I got very concerned about possible engine or tranny damage. Once I topped the hill the temp gauge went back to normal. It was in the high range for about 15-20 minutes. The Yukon runs fine ever since that happened and I learned I should have used manual mode and kept the RPM around 4000 to help cooling. Do you think I should be concerned?

 

[Marky Dissod]

I recently was pulling my camper up up a 7% grade, 7 miles long and the temp gauge went up to the last mark before hitting 260F red mark.
I estimate the temp gauge was at 245F-250F. No engine overheating warning messages came on dash. I was doing around 40-45 MpH.
I got very concerned about possible engine or tranny damage

AFTER THE FACT

Once I topped the hill the temp gauge went back to normal.
It was in the high range for about 15-20 minutes.
The Yukon runs fine ever since that happened, and I learned I should have used manual mode and kept the RpM around 4000 to help cooling.
Do you think I should be concerned?

Short answer: YES!
Longer answer: I am a pessimist, certainly, when compared to the above.
The amount of money someone would have to pay me to let coolant AND/OR ATF temp REACH 230F -
nevermind exceed 239F -
would cover the purchase of 2 or 3 used GMT800s in serviceable condition ... JUST IN CASE.

At the bare minimum - say, you're an optimist, and you also rolled a natural '20' -
since you did not mention changing your motor oil / ATF / antifreeze
you should not only change them NOW, you may also want to analyze the used fluids to
determine any damages.

The balanced way of looking at this:
Ever see pics of prez obama before vs after presidency? He looks like he aged more than 8 years,
because he DID. admin, lean back, I'm not tryna get political ... HERE. Point is:

You DEFINITELY prematurely aged your engine transmission AND cooling system up that 7% grade;
you ought to change your motor oil / ATF / antifreeze IMMEDIATELY.

Next time, use Tow / Haul mode, AND avoid towing in 5th / 6th / 7th / 8th, especially uphill.

 

[Larry Brew]

By the way, I just had a radiator flush and changed the Coolant a week before the trip and was towing in trailer mode when this happened!

 

[15burban]

How heavy was the camper you were towing? To a certain extent it doesn't really matter (coolant flush, etc) if you were towing more then it's rated for.

 

[swathdiver]

I recently was pulling my camper up up a 7% grade, 7 miles long and the temp gauge went up to the last mark before hitting 260 red mark. I estimate the temp gauge was at 245-250. No engine overheating warning messages came on dash. I was doing around 40-45 MPH. I got very concerned about possible engine or tranny damage. Once I topped the hill the temp gauge went back to normal. It was in the high range for about 15-20 minutes. The Yukon runs fine ever since that happened and I learned I should have used manual mode and kept the RPM around 4000 to help cooling. Do you think I should be concerned?

Hey Larry, what gear did you run that grade in? Since the cooling system had recently been serviced, it is possible that there is/was a bubble in the system and it was not a full capacity. You'll have to check that.

If yours were mine I would change the transmission fluid after that run. If it had been recently changed, I would change it at about 20K miles, 1/2 of the severe service schedule.

 

[Geotrash]

I recently was pulling my camper up up a 7% grade, 7 miles long and the temp gauge went up to the last mark before hitting 260 red mark. I estimate the temp gauge was at 245-250. No engine overheating warning messages came on dash. I was doing around 40-45 MPH. I got very concerned about possible engine or tranny damage. Once I topped the hill the temp gauge went back to normal. It was in the high range for about 15-20 minutes. The Yukon runs fine ever since that happened and I learned I should have used manual mode and kept the RPM around 4000 to help cooling. Do you think I should be concerned?

As a fellow heavy camper puller, I feel your pain. But in my opinion, if the coolant didn't boil (~260ºF), then you likely did no damage. But I also agree that something else is going on there for coolant temp to get that hot on a 5.3 towing up a 7% grade. I do that often here over the Appalachians and the hottest I've seen is 230-235ºF on a 95º day. And this is with a modified 6.2L putting out much more power and heat than a 5.3, with essentially the same cooling system.

I agree with James that you may have had some air trapped in the system, or perhaps you have a cooling fan not functioning right. We've also seen the factory radiators lose efficiency after 8-10 years and maybe 160K miles. Hard to say without more information in your case, but I would begin the troubleshooting process. And I also agree with James and Mark that an oil and transmission fluid change are both wise after a near-overheat event like that.