Transmission Cooler

I have an '09 31QBS pulled by an '05 Yukon XL SLT. I don't know what the rear end ratio is (How do I find out?). Anyway, I wanted to get opinions on the value/usefullness of adding a transmission cooler. With my current set-up, I don't have a transmission temperature gauge, so I'm flying blind. I'm moving to Florida this summer and I'm worried about pulling a heavy load in the heat. Any thoughts?
 

Ray LeTourneau

Senior Member - Past Moderator
Rich, Did your Yukon come with the Towing package? Chances are if it had the hitch on it already you have the towing package and it includes a factory trans cooler. It wouldn't hurt a thing to add a second cooler. I assuem when you tow you have the trans in "tow haul" mode. This raises your shift points to 2500 RPM and is better for the transmission. As long as you aren't over your towing capacity you should be fine.
 
It does have the factory tow package and I do use the "tow haul" mode, but I don't see anything about an external transmission cooler in any of the literature I have.
 

westxsrt10

Perfict Senior Member
I have an '09 31QBS pulled by an '05 Yukon XL SLT. I don't know what the rear end ratio is (How do I find out?). Anyway, I wanted to get opinions on the value/usefullness of adding a transmission cooler. With my current set-up, I don't have a transmission temperature gauge, so I'm flying blind. I'm moving to Florida this summer and I'm worried about pulling a heavy load in the heat. Any thoughts?

I hope you have better luck with your Yukon than us (2007). We towed a 5000# trailer and the truck couldnt take it. The weak spot was the rear end then the transmission. We traded our 6000 mile Yukon in while it was at the dealer getting a new rear end and trans. I'd get a MagHytec rearend cover for sure!
 

Ray LeTourneau

Senior Member - Past Moderator
Rich, The trans cooler is in there somewhere but it's not very big and that's why I mentioned it wouldn't hurt to add an after market cooler. Easy install and not very expensive. I forgot to mention. You have two options to determine your axle ratio. If you bought your truck new and saved the window sticker it should be on that. You can also have any dealer run your VIN and they can tell you. OR the old fashioned turn a rear tire one revolution and count the turns of the drive shaft. Probably very close to 3 and 3/4 turns which would translate to a 3:73 to 1
 
Hey Ray! I scoured the window sticker and couldn't find the number. I laughed out loud when you explained the old-fashioned way to determine the ratio! You'd think an engineer worth his salt would have figured that out! Duh! Thanks for the input. I'll probably have the guys down at GMC install an external cooler for me. It'll probably cost me twice what it should, but I don't want to take any chances on voiding my warranty (I have 70,000 miles left!) Can't wait to take my new trailer camping!
 

bigredtruck

Well-known member
AFter overheating on the way to Disneyland going up the 'Grapevine', we got a transmission cooler installed in Anaheim $250 all in. Couldn't beat the peace of mind on the way home :)
 
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