07 denali, 6.2 with muffler and full tune. Fans are on high but when pulling the boat last weekend the engine kept getting up around 225 and staying awhile before going back to 210. Tranny never got over 205 until the engine got warmer. Towing in fifth gear at 70 plus mph and the coolant was flusjed just a couple of nonths back at 70/30 mix. Whay might be the problem here? I was advised to leave the stock stat in it for fuel economy so i did.never any problems without the load behind it. Thanks Ryan

 

how heavy is the boat?

 

Texas weather id change that stat and add a tranny cooler

 

Man if your just going off that little temp gauge on your dash then its wrong. My temp gauge always shows 210° all the time but when logging on efilive it shows to never go over 196°

 

Onetogofast,
I have the same problem out here in Phoenix. I changed all my cooling parts last year and now when I pull the boat it will go to 225+ and once hit 255. Since I don’t know which part is not up to par I just replaced the waterpump(again) and T-stat yesterday. I won’t be able to get out with boat for 2 weeks so unsure if that will help. If that doesn’t get it I guess next will be to change to the 34inch radiator and ditch the 28 that is in there now. But that means new e-fans also. Hope it doesn’t get to that. Good luck to you as well as myself.

 

The boat and trailer is around 5000lb or so, its as tall as the yukon plus the windshield and tower hang up above pretty high. Tower collapses but not safe enough for travel. I was thinking that possibly the tranny getting warmer and the temp together were making everything get hot as one since the tranny cools through the radiator as well. Tranny cooler is in my mind for asap but my wife DD's this thing a lot more than it tows so the fuel mileage cut for doing the stat might not be worth it. The tranny never got over 217 so I wouldnt think the coolant got as hot as it sad or the tranny should have kept climbing. For it being GM's top of the line, "THE DENALI" you would think the tranny cooler would be bigger already, and mine does not have an oil cooler and it has the smaller radiator. I just dont understand these engineers....

 

I think they're overly influenced by the bean counters ....

 

My Denali came with a cooler but just not big enough lol

 

WHAT!!!! That's panic zone for me.

<< Ignorant to the Denali's, but what trans did they put in that monster?

 

It has a 6L80E in it. 217 had me worried but it would get high and drop back to 199 or so and stay for a long time then peak again for a few miles and drop and stay for 40 miles.