I installed a Hayden rapid-cool Model 679 transmission cooler on my Yukon xl with a 5.3L. It already had a tiny little "towing package" auxiliary transmission cooler in front of the radiator (the integrated radiator for the engine also brings trans fluid up in temperature and then provides some cooling, I think), but my new Hayden cooler sits off to the right and only about 1/2-2/3 of it gets direct airflow through the grille. It doesn't matter, because is seriously makes a difference. I swear to you it makes the transmission temp at least 50 degrees cooler. No kidding.
It's winter now and freezing-*** cold and the transmission rarely makes it up to 110 when not towing. I was worried about being to cool, but in 30 degree weather, the trans temp jumps quickly to about 75 degrees in just a few minutes, then takes about 15 minutes to get up to 95-98.
Before the addition of the Hayden cooler, I towed an RV in 96 degree weather this summer with lots of stoplights to go thru. Cruising, it would hold fast at 180's, but climbed to 192 when we reached our campground and then 203 just as I parked. I said screw it, and added the Hayden cooler. Then we made the same trip (much cooler weather, about 70-80 degrees out), but the trans temp stayed at 126. It did go to 136 once at a lot of intersections, but then COOLED off while cruising. Different ambient conditions, but still obviously much cooler transmission.
Pretty easy to put in once I got the courage and time. It is in series with the little aux cooler. Hayden guy said it should work but to just watch for pressure drop. I don't know how I'm supposed to watch for that, except by watching temp.
I do believe this DOES take a little bit of work off the main radiator (which supposedly, questionably, cools transmission).
Plus, if one of my coolers somehow fails or leaks, I can readily just unsnap it and take it out of the system.
And I tow almost 8,000 lb. My Yukon XL was rated for 5k, but I added Air Lift bags to rear coils for 1,000 tongue wt cap, use wt-distributing hitch, EBC "yellow stuff" dimpled/slotted brake pads/rotors, and importantly, I changed the axle ratios from soccer-mom 3.08 to bad-*** 3.73. Sure, my non-towing gas mileage really sucks, but I use 93 octane to make the wallet pain too intense to even feel.
I believe it suck that car makers can't stick a $60-80 big transmission cooler in there that will vastly increase the life of the transmission.
I have pictures if anyone is interested.
