Transmission reached 300F reversing trailer up a mountain

[tiwillia]

2017 GMC Sierra Denali 4x4 6.2, 8-speed auto, 51.5k miles

 

I was hauling a trailer full of maple hard wood here in the Appalachians, probably ~3500lbs. I had to reverse the trailer up a long (1/4 mile), steep (13 degrees according to the 4x4 info screen) driveway to get it to where it needed to be unloaded. About 95% of the way up the hill I noticed a burning smell. I continued since I was on the steepest part and just about at the top. Once I parked, I look at the trans temp guage and its just under 300F.

I shut off the truck immediately and let it cool down to ~210F while unloading before driving the truck back down the mountain. There were no leaks that I can see. The truck drove home with the empty trailer as normal without any issues. I had a transmission flush about 500 miles ago prior to this @ 51k miles, so it has brand new transmission fluid in it.

Looking for opinions on two questions:

1. What would you do next? Ignore it? Get the transmission drail & filled? Get the transmission flushed again?
2. Is there any way short of dropping the transmission pan to check the color/smell of the fluid? What should I check besides visually verifying there were no external leaks?

Edited November 12, 2020 by tiwillia
Clarification

[diyer2]

IMO

I would not have shut the truck off. I would have let it sit at idle to cool off trans. I do it when my trans gets warm 200-205 from towing my boat up the grade to our house. I switch the DIC to trans temp and watch it cool off. 

I think shutting it off raises the temp because it has to cool by disipating the heat instead of cooling with fans and trans fluid cooler. 

I would replace the fluid. No flush. 

[tiwillia]

I think you're right, in hindsight it would have made more sense to idle the truck. I was just shocked that it had reached that temperature and probably didn't think it through. Thanks for your input.

[UnlimitedMatt]

I can't answer your question but wanted to share what I do when towing in similar situation.  I always make sure I'm in 4x4 low range to take advantage of the lower gearing.   

[truckguy82]

Yes flush it asap, that fluid is toast.

[flyingfool]

torque converter clutch is probably dead too, this is the area of highest temp. in a transmission and probably 100 F hotter than that displayed on the gauge

 

1. new fluid.

2. thermostat delete, or pill flip

3. Katech 175 engine stat

4 use Ester oil in motor and trans

Edited November 12, 2020 by flyingfool

[newdude]

4 hours ago, tiwillia said:

2017 GMC Sierra Denali 4x4 6.2, 8-speed auto, 51.5k miles

 

I was hauling a trailer full of maple hard wood here in the Appalachians, probably ~3500lbs. I had to reverse the trailer up a long (1/4 mile), steep (13 degrees according to the 4x4 info screen) driveway to get it to where it needed to be unloaded. About 95% of the way up the hill I noticed a burning smell. I continued since I was on the steepest part and just about at the top. Once I parked, I look at the trans temp guage and its just under 300F.

I shut off the truck immediately and let it cool down to ~210F while unloading before driving the truck back down the mountain. There were no leaks that I can see. The truck drove home with the empty trailer as normal without any issues. I had a transmission flush about 500 miles ago prior to this @ 51k miles, so it has brand new transmission fluid in it.

Looking for opinions on two questions:

1. What would you do next? Ignore it? Get the transmission drail & filled? Get the transmission flushed again?
2. Is there any way short of dropping the transmission pan to check the color/smell of the fluid? What should I check besides visually verifying there were no external leaks?

 

 

Who did the flush and did they use the correct fluid?

 

Was the filter changed?

[elcamino]

Above 270ºF, certain internal components, such as seals, begin to disintegrate rather quickly. Some 100% synthetic fluids such as AMSOIL can withstand higher temperatures above 270 but not ordinary Dexron. 

[txab]

 

 

Replace the fluid and drive it 'till it dies

Edited November 13, 2020 by txab

[Grumpy Bear]

8 minutes ago, txab said:

 

What? No butter?

 

 

Edited November 12, 2020 by Grumpy Bear

[Grumpy Bear]

Yes it got hot enough to damage everything in the box IF it was that hot long enough.

Question is was it hot LONG enough?

 

Damage is the result of heat and time.

Fact that it drove back fine is good news. 

 

Don't worry about the converter clutch.

It doesn't lock up in lower gears or reverse.

Change ALL the fluid.

Time will tell the rest. 

 

 

[CamGTP]

The torque converter will lock in every forward gear on the 8 speed if my memory is right but not in reverse.

 

The reverse plus a long hill with weight will put tons of heat into the fluid for sure.

[Grumpy Bear]

2 hours ago, CamGTP said:

The torque converter will lock in every forward gear on the 8 speed if my memory is right but not in reverse.

 

The reverse plus a long hill with weight will put tons of heat into the fluid for sure.

Good to know about the 8 speed. Thanks! 

[Colossus]

get it flushed again. 

[heymrdjCW]

These situations are why RV haulers like manually unlocking hubs. That way they can unlock the front and still have 4x4 low reduction when they reverse the heavy things up steep inclines. Takes a lot of work off the transmission when you can run it through Low.