2009 Yukon Denali AWD High Transmission Temps - SOLVED

[Geotrash]

You need a tru cool 40k transmission clller for that thing 150$ it dropped my temps from that down to 165-175 mine would run hot all the time too in traffic until I upgraded it

The Trucool 40K seems to work great on 5.3 rigs, but not on 6.2's when towing heavy. See my post above.

 

[Geotrash]

Rokjhn, if your vehicle lives and drives in a climate where cold winters are irrelevant, feel free to bypass the ATF preheater in the radiator.

I experimented with this a few years ago. When I added my Derale cooler to my 2012, I first cut the radiator end tank cooler out of the loop. The result was much higher transmission fluid temperatures when cresting a mountain pass we frequently tow over on hot days (260ºF). I plumbed the end tank cooler back into the circuit and it solved the problem, dropping fluid temp to 230ºF or below on the same pass in similar weather. So, the end tank serves as a fluid pre-heater when the fluid is cold, but it also takes a significant first cut of heat out of the fluid when towing in hot weather.

And indeed, the GM upfitter manual states that external fluid coolers should be plumbed in series after the radiator end tank cooler.

 

[j91z28d1]

but he's not towing.. he's got tow Temps engine and trans without towing anything?

on a ls and heat note, I don't have a the tow experience, but I can tell you from a ls1 to a ls3 on the sports cars side.. the ls1 never has temp issues, coolent or oil. doesn't matter the platform, camaro, gto and c5. once you get to 6.2L ls3 cars, like a newer c6 and camaros, they over heat like crazy but only after 08,before then they had the Ls2 6.0L and it seemed to OK. ls3 oil Temps can hit 300 in stock form from just a fun back road run, tons of issues on track days and that's manual cars. the auto cars, I've seen posts of guys not getting 2 laps before the car goes into limp mode for high trans Temps. camaros not as bad, but corvettes it takes a 1000$ oil cooler and 800$ radiator plus fan mods to keep a stock one cool if you work it hard at a open track day.


kinda wild you guys see the same thing from the 5.3 to the 6.2. oddly the 7.0L ls7 doesn't really have these issues while making almost a 100more hp

I came from a ls1 car beat it to death, no oil cooler or or aftermarket anything cooling wise. got a ls3 and thought it was broken or had a bad head gasket, it over heated it's oil so badly, even with the oem front mount oil cooler.

this 6.0 hybrid probably has the biggest front mount tranny cooler I've ever seen on a stock vehicle. it's basically the size of the ac condenser with 5/8s lines going to it.

 

[Geotrash]

but he's not towing.. he's got tow Temps engine and trans without towing anything?

Yes, I understand that. But his temps are normal for just the plain ol' truck with nothing in tow. I mentioned the towing information because 1/ they show how much more headroom he has for transmission fluid temps before he needs to worry. And, 2/ they show what happens closer to the limits with the various remedies being discussed.

on a ls and heat note, I don't have a the tow experience, but I can tell you from a ls1 to a ls3 on the sports cars side.. the ls1 never has temp issues, coolent or oil. doesn't matter the platform, camaro, gto and c5. once you get to 6.2L ls3 cars, like a newer c6 and camaros, they over heat like crazy but only after 08,before then they had the Ls2 6.0L and it seemed to OK. ls3 oil Temps can hit 300 in stock form from just a fun back road run, tons of issues on track days and that's manual cars. the auto cars, I've seen posts of guys not getting 2 laps before the car goes into limp mode for high trans Temps. camaros not as bad, but corvettes it takes a 1000$ oil cooler and 800$ radiator plus fan mods to keep a stock one cool if you work it hard at a open track day.


kinda wild you guys see the same thing from the 5.3 to the 6.2. oddly the 7.0L ls7 doesn't really have these issues while making almost a 100more hp

I came from a ls1 car beat it to death, no oil cooler or or aftermarket anything cooling wise. got a ls3 and thought it was broken or had a bad head gasket, it over heated it's oil so badly, even with the oem front mount oil cooler.

this 6.0 hybrid probably has the biggest front mount tranny cooler I've ever seen on a stock vehicle. it's basically the size of the ac condenser with 5/8s lines going to it.

Interesting stuff that confirms that the 6.2 is hot blooded. Check it and see!

 

[donjetman]

One thing I did notice though on the Yukon was that when the Transmission was at 235, the engine temp went up and matched it. I'm assuming that's because of the hot transmission fluid flowing thru the cooler?

I've never seen my transmission temp above 210. But I don't do any stop a go driving or towing. My engine temp never goes above 210*f on the gauge.
We use the Denali in extreme conditions. 110* TX, NM heat, and -20* cold in the winter CO mtns.

 

[j91z28d1]

I was thinking they never ran that hot unloaded and if it is, while fine for now, it's taking away any built in overhead for towing.

I still want to get mine front 210ish around town down to 200. need to find me a quality 180 stat.

 

[donjetman]

the ls1 never has temp issues, coolent or oil. doesn't matter the platform, camaro, gto, or c5

???
I have a stock ls1 powered c5. I'm on all the c5 corvette FB groups and forums. I read constantly about them over heating when stop and go driving their ls1 powered c5 vette.

 

[Rokjhn]

Thank you all for the insight. Never occurred to me to check the electric fans, but sure enough the passenger side fan was not coming on. Replaced it this morning and did same drive as yesterday and the transmission temp stayed in the 170-180 range. Think I’ve resolved my issue for now! Thanks!

 

[Joseph Garcia]

Very interesting discussion on transmission temps. I've never seen a transmission temp above 165 degrees on my 2007 Yukon XL Denali with the 6.2 Black Bear tuned motor, but I live in NH, and I do not tow anything significant. But, I do drive it like I stole it. I've probably just freakin' jinxed myself.

 

[Joseph Garcia]

Thank you all for the insight. Never occurred to me to check the electric fans, but sure enough the passenger side fan was not coming on. Replaced it this morning and did same drive as yesterday and the transmission temp stayed in the 170-180 range. Think I’ve resolved my issue for now! Thanks!

What happened? Did you forget to re-connect the fan's electrical connector?