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.