I'm about to pull my first boat (21 foot cobalt) with my new 2011 3/4 ton burb. It's probably still near 100 degrees in the desert and I have to get over a pretty steep grade here in So Cal (Cajon Pass). It has the stock trans cooler and I'm wondering:
A. What would you guys expect the trans temp to be at on the flat areas?
B. What is the highest temp the Trans should ever get to?

Thanks.

 

At 100*, I'd expect something in the 210-220* range. Check w/ a couple of dealers to see what they say.

 

Frankly, your truck should have no problem pulling that boat. I'd expect to see only slightly higher-than-normal trans temps.

I would expect to see the transmission in the 210-220° range. I would get worried and pull over if it ever got above 240°. There is some temperature where the truck will give you the message to pull over and idle the motor to let the transmission cool down.

On our vacation last month, I pulled my 6500-lb travel trailer through Colorado (including the Eisenhower Tunnel and Vail Pass), and also did some moderate four-wheeling in 100°+ temperatures in the Moab, UT area. In both situations, the trans temp was in the 225-230 range. Highest temperature it saw was 235°.

Now, what I did do while we were in Moab was pop the hood and let the engine idle with the hood open a few times when we stopped to take photos. This got the trans temp back down around 210° after 5-10 minutes. When I opened that hood, you could feel the blast of heat coming from the engine and radiators.

I also have a few friends who work for GM, including one who works in one of their transmission test labs. He told me Dexron VI has much higher/better properties than Dexron III. Thermal degradation is accelerated when the temperature exceeds 270° F.

Here's a pic as we were ascending the final hill towards the tunnel (outside temp was 75°):

 

230 seems pretty high. At what point does one consider a larger aftermarket cooler?

 

If you are going to tow more than a couple of times a year or for any extended distances, i would recommend adding the auxiliary transmission cooler...

 

The weak link in an automatic transmission is the fluid. All of the other components can handle the elevated temperatures. As I mentioned earlier, Dexron VI starts to degrade severely at 270°. So I was not concerned that the transmission was running at 230°. I confirmed this with a close friend, who is a transmission engineer at GM. I respect and trust his opinion.

Aftermarket coolers are discussed frequently, but the bottom line is that they're unnecessary, particularly with Dexron VI transmissions. The manufacturers test their vehicles under "worst case" conditions. You can go to Arizona, Death Valley or Pikes Peak, and you will surely see some test mules loaded up with instruments and sensors.

As an aside, I've been in the seal business for over 20 years. About a third of my business is to Tier 1 automotive suppliers, including transmission manufacturers. I call on companies like ZF, Aisin, and Master Automatic. It's my job to know how my products, and rubbers and plastics in general, are affected by elevated temperatures.

 

Hey guys,
I wanted to resurrect this topic for a moment. So as luck would have it, somebody back into the Suburban while trying to parallel park in front of the vehicle. The damage is all to the front bumper and it's not terrible. The other owner was cool, we exchanged info and they want to pay for the damage. I took it to the shop that's been servicing our vehicles for the past 10 years. He said they'll need to remove the front bumper clip to do the repairs.

So here I am with a golden opportunity to upgrade the OEM transcooler to a bigger nice B&M. The shop said they'd put it in for free if I brought them the unit. Sweet.
I'm trying to figure out if it's necessary though. We took two trips to Lake Havasu with our new boat this past summer. It was late in the season and it was only mid 90's outside. On Cajon Pass (a pretty steep grade out here in So Cal), the tranny temp got as high as 210*. I expect the outside temps to reach 110* on some trips out there. The boat is 26' long and weighs 6500-7000 lbs depending on the gear we take.

I don't want to replace the cooler if I don't have to. But now is the time to do it if you guys think I should. Curious to hear your feedback. Thanks!

 

Unless you tow a lot, I'd say stick with the OEM one if there is nothing damage on it... 210 is not an issue for a short periods, its extended high temps that cause the fluid breakdown... my 2¢

 

My close friend works at General Motors. His job is validating/testing transmissions. When he started at GM, his first job was validating the 6L80/6L90 transmissions.

I asked him about installing an aftermarket cooler in my Burb. His response: "It's completely unnecessary. We've done much worse to those transmissions than you'll ever do."

The transmission warning message comes on when the fluid temperature hits 265°. Even when I was beating the snot out of my truck, it never went above 235°.