Keeping coolant and transmission temps under control when towing in the summer heat

[Geotrash]

Found this little nugget as well that might be helpful:

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."

Finally, I've seen a bunch of charts that show transmission life vs. fluid temperature. Apparently they're all hogwash, and based on very outdated information using older generations of fluids. GM's own manuals tell a different story. The charts more accurately depict transmission fluid life for older generations of fluid than Dexron VI, and not transmission life.

 

[avalonandl]

Dexron 6 is designed to work until 260 with no issues.

Those old charts that show "damage" above 210 are BS......

 

[wsteele]

Found this little nugget as well that might be helpful:

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."

Finally, I've seen a bunch of charts that show transmission life vs. fluid temperature. Apparently they're all hogwash, and based on very outdated information using older generations of fluids. GM's own manuals tell a different story. The charts more accurately depict transmission fluid life for older generations of fluid than Dexron VI, and not transmission life.

Thanks for sharing.

My anecdotal experience has zero statistical significance, but weighs on my point of view about transmission temps, modern ATF replacement cycles, etc. My 5.3L, 4 speed Yukon SLT, integrated trans cooler (much different than your 6.2L, 6 speed, with 24kt gold cooling) did tow duty for its first 60K miles or so, a lot of tow duty. I pulled a 5K lb enclosed trailer all around the west (occasionally even to the GM experts worst case scenario location, Willow Springs Raceway, Rosamond CA).

Trans temps very rarely got above 230F and never anything close to the 285F the GM expert says is the red line for Death Valley towing. As per my owners manual, I changed the transmission fluid at 50K miles along with the filter. At 76K miles, just outside Reno NV on Interstate 80, my transmission decided it had enough. A reman transmission was the prescribed repair.

I hear what the GM guy is saying, but frankly, if I was still pulling 5K around, I would have already upgraded to your setup and would change my Dexron VI and filter every 25K miles. Even if it didn't statistically do anything for the longevity, it would make me feel like maybe anecdotally it might.

 

[Geotrash]

Thanks for sharing.

My anecdotal experience has zero statistical significance, but weighs on my point of view about transmission temps, modern ATF replacement cycles, etc. My 5.3L, 4 speed Yukon SLT, integrated trans cooler (much different than your 6.2L, 6 speed, with 24kt gold cooling) did tow duty for its first 60K miles or so, a lot of tow duty. I pulled a 5K lb enclosed trailer all around the west (occasionally even to the GM experts worst case scenario location, Willow Springs Raceway, Rosamond CA).

Trans temps very rarely got above 230F and never anything close to the 285F the GM expert says is the red line for Death Valley towing. As per my owners manual, I changed the transmission fluid at 50K miles along with the filter. At 76K miles, just outside Reno NV on Interstate 80, my transmission decided it had enough. A reman transmission was the prescribed repair.

I hear what the GM guy is saying, but frankly, if I was still pulling 5K around, I would have already upgraded to your setup and would change my Dexron VI and filter every 25K miles. Even if it didn't statistically do anything for the longevity, it would make me feel like maybe anecdotally it might.

I’ll bet that was a painful breakdown! We’re you able to get it fixed while you waited?

Thanks for sharing your thoughts about the relative towing reliability of something like the Denali with the 6L80E vs the old 4L60. I had one of those in my old ‘02 Suburban. It never gave me any trouble but it had been rebuilt by the time I bought it.

Hopefully this Denali will be dialed in now, but we still have some trips to make before I’m 100% on the transmission cooling setup. More to come!


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[wsteele]

I’ll bet that was a painful breakdown! We’re you able to get it fixed while you waited?

Thanks for sharing your thoughts about the relative towing reliability of something like the Denali with the 6L80E vs the old 4L60. I had one of those in my old ‘02 Suburban. It never gave me any trouble but it had been rebuilt by the time I bought it.

Hopefully this Denali will be dialed in now, but we still have some trips to make before I’m 100% on the transmission cooling setup. More to come!


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I think all breakdowns are painful on the road far from home. This one was particularly tough as I was commuting down to UC Davis Vet hospital, trying to keep the best dog we ever had alive. She had a bad form of cancer and UC Davis was our only hope, so I was driving back and forth weekly from Idaho.

I got a wonderful tow truck driver, he took me and our dog to a great transmission shop. The guy at the shop got me a rental car, help transfer all our crap to the rental and did the transmission replacement in a day and had my truck ready for us on our return trip back through from our dog's chemo treatment. The whole bill was just a smidge over $2300. The transmission has been trouble free since (coming up on the same mileage as the last one soon, but little towing and regular service probably means we should be good for a long time to come).

Bullet proofing the transmission makes a ton of sense to me.

 

[thompsoj22]

Some more data for those of you following along and for those considering this path. Picked up the camper this morning with an ambient temp of around 70ºF. It's about a 10 mile drive to the storage place each way - most of it on I-95. On the way out, the transmission temp hovered around 175ºF on the highway and was up to 180º once I slowed down and was maneuvering around the lot. The Derale's fan didn't need to come on. After picking up the trailer, on the highway, my transmission temp hung around 185-190ºF, also likely below the fan threshold. Once I got off the highway though, the temperature quickly rose to 199ºF and peaked at 205ºF as I maneuvered around the neighborhood and arrived at the house, but quickly settled back down to 198ºF once I stopped and was idling in park for a minute.

Engine coolant temp never broke 200ºF in either direction. So far, this seems to be a win for engine cooling, and I'm cautiously optimistic that it'll be able to keep the transmission cool enough (below 215ºF on the hills) when towing in warmer weather - especially on the highway. More data to come this weekend.

Does this jibe with what you guys who also have the Derale see when towing?

Ditto on the average temps while towing. Just to clarify, Did you eliminate the radiator heater when you installed the DERALE?

 

[thompsoj22]

Some more data for those of you following along and for those considering this path. Picked up the camper this morning with an ambient temp of around 70ºF. It's about a 10 mile drive to the storage place each way - most of it on I-95. On the way out, the transmission temp hovered around 175ºF on the highway and was up to 180º once I slowed down and was maneuvering around the lot. The Derale's fan didn't need to come on. After picking up the trailer, on the highway, my transmission temp hung around 185-190ºF, also likely below the fan threshold. Once I got off the highway though, the temperature quickly rose to 199ºF and peaked at 205ºF as I maneuvered around the neighborhood and arrived at the house, but quickly settled back down to 198ºF once I stopped and was idling in park for a minute.

Engine coolant temp never broke 200ºF in either direction. So far, this seems to be a win for engine cooling, and I'm cautiously optimistic that it'll be able to keep the transmission cool enough (below 215ºF on the hills) when towing in warmer weather - especially on the highway. More data to come this weekend.

Does this jibe with what you guys who also have the Derale see when towing?

Ditto on the average temps while towing. Just to clarify, Did you eliminate the radiator heater when you installed the DERALE?

 

[Geotrash]

Ditto on the average temps while towing. Just to clarify, Did you eliminate the radiator heater when you installed the DERALE?

Yes, I did. Both lines run from the transmission directly to and from the Derale cooler.

 

[Geotrash]

Just another update for y’all. This setup ain’t gonna work as it is. Pulled the camper over the blue ridge on a steep pass (highway 211) crossing over the skyline drive, 87° ambient temp. Transmission temp started at 208° at the bottom and rose to 261° at the top, then took 20 minutes to cool down to below 220° again after the descent while driving over gently rolling terrain. Coolant temps never got above 227°

Next step: I’m going to plumb the radiator’s cooler back into the system. My theory is that the oil to water cooler will help cut the peaks off the transmission fluid temp on a long pull like that, and that there is enough extra cooling capacity in the radiator to handle it.


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[HD_LS]

A lot of the heat generated in the transmission is from the Torque converter. What about having your tuner reprogram it to fully lock up the torque coverter, and keep it locked up, when you have it in Tow/Haul mode? I read that GM also has some kind of intentional % slip, when it is supposedly locked up, that can also be programmed out.

 

[03_GMC]

Just another update for y’all. This setup ain’t gonna work as it is. Pulled the camper over the blue ridge on a steep pass (highway 211) crossing over the skyline drive, 87° ambient temp. Transmission temp started at 208° at the bottom and rose to 261° at the top, then took 20 minutes to cool down to below 220° again after the descent while driving over gently rolling terrain. Coolant temps never got above 227°

Next step: I’m going to plumb the radiator’s cooler back into the system. My theory is that the oil to water cooler will help cut the peaks off the transmission fluid temp on a long pull like that, and that there is enough extra cooling capacity in the radiator to handle it.


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Hmmmm that’s interesting. I am going to install a 30 row American Volt cooler on mine but keep it plumbed through the radiator. It’ll have its own fan and also be mounted behind the lower grille with aluminum baffles to direct the air straight to the cooler.


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