2009 Yukon Denali AWD High Transmission Temps - SOLVED

[Rokjhn]

I installed a rebuilt 6.2l engine in my Yukon that I had picked up with a seized engine. Mild build with a Stage 1 TSP cam with BlackBear tune, kept the stock exhaust, original 6l80e transmission, torque converter, etc... everything is running as it should regarding oil pressure, engine temps, etc.. I'm about 1000 miles into the break-in and noticed that the transmission temperature on the DIC went as high as 235 degrees when in stop-and-go traffic on a hot Houston day (100 degrees). Drove 17 miles this morning in moderate temps (85 degrees) and it got up to 205 degrees, again in town stop-and-go traffic. On the freeway, it stays between 180-190. It also has a new radiator, however, I reused the stock transmission cooler. No warning lights or codes, transmission shifts fine, and the fluid still looks and smells new. Not sure what would cause it to spike that high or am I worried about nothing? Should I upgrade the cooler?

 

[petethepug]

Welcome from SoCal, thank you for calling out the trucks description out front. I drove my 09 Denali clone from TX to CA and the trans did run warm when I got stuck in construction traffic on the highway.

You’ve got a slight increase in performance on the motor which is likely taken the trans cooler to the far end of it’s capability when the front & rear a/c are balls out.

Just update the trans cooler one size up. Some of the other guys will chime in about adding a t stat or not and a good replacement for the trans cooler. Post up a pic of the truck when you when you get a chance.

 

[Geotrash]

I installed a rebuilt 6.2l engine in my Yukon that I had picked up with a seized engine. Mild build with a Stage 1 TSP cam with BlackBear tune, kept the stock exhaust, original 6l80e transmission, torque converter, etc... everything is running as it should regarding oil pressure, engine temps, etc.. I'm about 1000 miles into the break-in and noticed that the transmission temperature on the DIC went as high as 235 degrees when in stop-and-go traffic on a hot Houston day (100 degrees). Drove 17 miles this morning in moderate temps (85 degrees) and it got up to 205 degrees, again in town stop-and-go traffic. On the freeway, it stays between 180-190. It also has a new radiator, however, I reused the stock transmission cooler. No warning lights or codes, transmission shifts fine, and the fluid still looks and smells new. Not sure what would cause it to spike that high or am I worried about nothing? Should I upgrade the cooler?

Completely normal. The system is working as intended. I have studied this particular topic to death and there is a lot of incorrect information on transmission fluid items out there. Here is GM's guidance on it:

xxxx

In the February 2011 issue of Trailer Life magazine RV Clinic in response to a reader about the maximum transmission temperature allowed in a 2009 Chevy Silverado, the Tech Team had this response.

“General Motors’ in-house towing team expert provided RV Clinic with this statement: The maximum allowable automatic transmission fluid temperature is dictated by the transmission oil itself. The oil begins to degrade significantly above 270 degrees Fahrenheit, so we design vehicles so that in all but the most extreme conditions, the fluid temperature in the transmission sump stays below 270 degrees F.

We allow for up to 285 degrees F in extreme conditions (i.e. towing a trailer with combination loaded at GCWR in Death Valley). But for customer usage anywhere else in the country, even at GCWR, transmission sump temperature should stay well below 270 degrees F. Above this point, certain internal components, such as seals, begin to disintegrate rather quickly. Although newer synthetic fluids can withstand higher temperatures we still recommend this (270F) as a maximum temperature. "

xxxx

For my part, I will sometimes see transmission fluid temps up to 235 when towing heavy up long 7% grades at the peak of summer, but most of the time when towing I'm right around 195-205 on the highway and around 190 when not towing.

 

[Rokjhn]

Completely normal. The system is working as intended. I have studied this particular topic to death and there is a lot of incorrect information on transmission fluid items out there. Here is GM's guidance on it:

xxxx

In the February 2011 issue of Trailer Life magazine RV Clinic in response to a reader about the maximum transmission temperature allowed in a 2009 Chevy Silverado, the Tech Team had this response.

“General Motors’ in-house towing team expert provided RV Clinic with this statement: The maximum allowable automatic transmission fluid temperature is dictated by the transmission oil itself. The oil begins to degrade significantly above 270 degrees Fahrenheit, so we design vehicles so that in all but the most extreme conditions, the fluid temperature in the transmission sump stays below 270 degrees F.

We allow for up to 285 degrees F in extreme conditions (i.e. towing a trailer with combination loaded at GCWR in Death Valley). But for customer usage anywhere else in the country, even at GCWR, transmission sump temperature should stay well below 270 degrees F. Above this point, certain internal components, such as seals, begin to disintegrate rather quickly. Although newer synthetic fluids can withstand higher temperatures we still recommend this (270F) as a maximum temperature. "

xxxx

For my part, I will sometimes see transmission fluid temps up to 235 when towing heavy up long 7% grades at the peak of summer, but most of the time when towing I'm right around 195-205 on the highway and around 190 when not towing.

Thank You Dave! That makes me feel better about the situation. My only other reference is my 2011 Avalanche (5.3l\6L80) rarely gets over 175 in the Texas heat, but it's probably a little lighter and not AWD\4x4. 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?

 

[tagexpcom]

I have 2021 6.2L / 10speed Yukon Denali and transmission gets up to 180s towing 5300lbs at 90F ambient at 60mph and mountain grades. Highest was ~200F towing 5300lbs up 10mile 6% grade 10miles on a 107F ambient afternoon at 60mph.

So I can see why you're paying attention as mine is <180F for normal driving but on the other hand I like the previous post by @Geotrash and 205F for normal driving might be OK. It really does get down to the design tolerances.

What year/transmission do you have?

 

[donjetman]

I installed a rebuilt 6.2l engine in my Yukon that I had picked up with a seized engine. Mild build with a Stage 1 TSP cam with BlackBear tune, kept the stock exhaust, original 6l80e transmission, torque converter, etc... everything is running as it should regarding oil pressure, engine temps, etc.. I'm about 1000 miles into the break-in and noticed that the transmission temperature on the DIC went as high as 235 degrees when in stop-and-go traffic on a hot Houston day (100 degrees). Drove 17 miles this morning in moderate temps (85 degrees) and it got up to 205 degrees, again in town stop-and-go traffic. On the freeway, it stays between 180-190. It also has a new radiator, however, I reused the stock transmission cooler. No warning lights or codes, transmission shifts fine, and the fluid still looks and smells new. Not sure what would cause it to spike that high or am I worried about nothing? Should I upgrade the cooler?

Temps seam normal to me. The 6L80 in ours runs 85* to 105*f above outside ambient temps. My Denali has a factory trans cooler, RPO code KNP. GMC labels it heavy duty but its NOT.
If I towed I would upgrade my cooler.

 

[Marky Dissod]

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.

 

[Trey Hardy]

I installed a rebuilt 6.2l engine in my Yukon that I had picked up with a seized engine. Mild build with a Stage 1 TSP cam with BlackBear tune, kept the stock exhaust, original 6l80e transmission, torque converter, etc... everything is running as it should regarding oil pressure, engine temps, etc.. I'm about 1000 miles into the break-in and noticed that the transmission temperature on the DIC went as high as 235 degrees when in stop-and-go traffic on a hot Houston day (100 degrees). Drove 17 miles this morning in moderate temps (85 degrees) and it got up to 205 degrees, again in town stop-and-go traffic. On the freeway, it stays between 180-190. It also has a new radiator, however, I reused the stock transmission cooler. No warning lights or codes, transmission shifts fine, and the fluid still looks and smells new. Not sure what would cause it to spike that high or am I worried about nothing? Should I upgrade the cooler?

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

 

[j91z28d1]

Thank You Dave! That makes me feel better about the situation. My only other reference is my 2011 Avalanche (5.3l\6L80) rarely gets over 175 in the Texas heat, but it's probably a little lighter and not AWD\4x4. 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?

if your engine coolent Temps were 235 as well from just driving around normally not towing or working it hard, something isn't right.

are both cooling fans coming on max? can you read the coolent temp from a scanner not just the dash gauge that's just kinda a guess. I've seen 10-15deg differences on my scanner and the dash gauge never more off straight up.

how old and how many miles on the rad?

the tranny could in theory add some temp to the coolent in the radiator, but it shouldn't be enough to over heat it, water to water is the best heat transfer, but it's not that good. these trucks have a fairly large cooling system, and byond towing and racing should never run 235.

 

[Geotrash]

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?

Yes, I believe so. I attribute it to having the transmission fluid coolers so intricately tied to the engine cooling system. The factory external transmission cooler sits in front of the radiator, dumping heat there, and the hot fluid exiting the transmission flows first through the end tank on the passenger side of the radiator, before entering the external cooler.

On my 2012, I replaced the factory external cooler with a Derale 13960 fan-forced plate cooler mounted below the front bumper and behind the lower grille. This had a modest decoupling effect between the transmission fluid and coolant temps when towing.

Side note, in my 2007, I mounted a Trucool 40K in the factory external cooler location in front of the radiator, and it's now unusable for towing our 7500 lb camper in the summer. The transmission fluid stays cool but the engine does not. Both trucks have radiators which are less than 2 years old.

Interestingly, this problem only seems to afflict the 6.2L trucks. Other people have noted the same problem with the Trucool on their Denali's, but 5.3 owners have not. My guess is that it's because the 6.2 puts out about 21% more power. More power = more heat but they both have the same cooling system.

 

[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?