"transmission hot idle engine" message alert setting

[GMCTom]

2018 GMC Yukon SLT
While taking a 1,000 mile trip to 9k elevation, my GMC Yukon alerted with a "transmission hot idle engine" message. I Let the vehicle cool for about 45 minutes, then resumed driving. The message alerted one more time, and I pulled over and let the vehicle cool for 20 minutes. No more alerts occurred that trip, but there were no more steep uphill legs either.

Question for the forum, what is the "transmission hot idle engine" message set to alert at?
After doing some reading on this forum, I set the dash to display the Transmission Fluid temp. so I could watch it. While the alert has not occurred again, the transmission fluid has reached a max temperature of 260. Trying to understand norms and if I have an underlying transmission issue that I need to look into.

Thanks in advance.

 

[Rygrego]

That's way too hot. I would replace the transmission fluid thermostat with the updated one from a year or two back. It will keep your fluid well below 190 degrees. Temps that high will soon leave you on the side of the road. The fluid in my 2016 SLT never exceeds 180 degrees with the updated thermostat and a Mishimoto trans cooler no matter the temp outside or whether I'm towing.

 

[15burban]

Along with the updated thermostat or just delete it I would replace your trans fluid asap. That fluid got cooked.

 

[Marky Dissod]

the ATF has reached a max temp of 260F.
Trying to understand norms and if I have an underlying transmission issue that I need to look into.

EVERY TIME the ATF hits 248F, it and the ATF filter need to be changed. EVERY TIME.

That's way too hot. I would replace the transmission fluid thermostat with the updated one from a year or two back.
It will keep your fluid well below 190F. Temps that high will soon leave you on the side of the road.

THIS.

 

[Rygrego]

Along with the updated thermostat or just delete it I would replace your trans fluid asap. That fluid got cooked.

I totally agree.

 

[GMCTom]

That's way too hot. I would replace the transmission fluid thermostat with the updated one from a year or two back. It will keep your fluid well below 190 degrees. Temps that high will soon leave you on the side of the road. The fluid in my 2016 SLT never exceeds 180 degrees with the updated thermostat and a Mishimoto trans cooler no matter the temp outside or whether I'm towing.

Thanks for the reply

 

[NickTransmissions]

Thanks for the reply

Drop the pan, inspect for burnt clutch material or any melted rubber material...Id also drop the valve body and replace the seals between the vb assembly and pump + center support as 240+ makes for crispy critters and melted sealing surfaces.

Do a complete flush, get all the old fluid out.

 

[GMCTom]

That's way too hot. I would replace the transmission fluid thermostat with the updated one from a year or two back. It will keep your fluid well below 190 degrees. Temps that high will soon leave you on the side of the road. The fluid in my 2016 SLT never exceeds 180 degrees with the updated thermostat and a Mishimoto trans cooler no matter the temp outside or whether I'm towing.

Thanks Rygrego, and all,
ODB code came back with a failed transmission fluid cooler thermostatic valve.
One valve ($131) and three seals ($10) fixed my issue
& yes I replaced the fluid, filter and pan.

Display now reads between 149 - 182 for Transmission Fluid temp

Thanks for the help on this - you all are great!

 

[Bagherra]

Got a part #?

 

[GMCTom]

GM Valve (Part# - 85585333)
GM Seal (Part# - 85628205)
GM Seal (Part# - 23277649) Needed 2

 

[Rygrego]

Thanks Rygrego, and all,
ODB code came back with a failed transmission fluid cooler thermostatic valve.
One valve ($131) and three seals ($10) fixed my issue
& yes I replaced the fluid, filter and pan.

Display now reads between 149 - 182 for Transmission Fluid temp

Thanks for the help on this - you all are great!

Fantastic!

 

[Bagherra]

GM Valve (Part# - 85585333)
GM Seal (Part# - 85628205)
GM Seal (Part# - 23277649) Needed 2

Thanx!!

 

[ComputernerdBD]

I second the cooler and bypass kit OR the updated one for sure having been there myself unfortunately but not as lucky as you were.... Mishimoto MMTC-K2-14 cooler and Surecool STL010 bypass kit along with a B&M B&M 70392 pan are all on my 2018 Z71 Midnight Edition now with a rebuilt transmission. The first two of those I ordered on Christmas Day off Amazon sitting in a tow truck after blowing my original transmission hours from home on Christmas Eve, the pan I ordered from there in 2022. It was at 65K miles just hours after it being offloaded from the Auto Train in Northern VA on Christmas Eve and at the time I was driving thru Baltimore. The torque converter started shedding metal and was hesitating/slipping/flare shifting so felt something was up and checked the temp gauge. Temps started climbing 2F every few seconds up 240F so pulled off the road into a gas station. Fluid was just changed less than two months before with nothing there and had the new pan on there since the previous change year before that so I knew once I got it off the road and saw glitter on the dipstick it was done. Let it cool and drove to a hotel in low gear and had AAA tow it back to NY almost 300 miles away on Christmas Day back to a shop close to home I trust with all three of my trucks. Now I have had it back for almost a month since all of the repairs (which also included a new condenser and lines due to the glitter) and about 1400 miles later running nicely no warmer than 128-130F at high speeds and only gets up to 135F in town but that is in the winter with no towing and the aero shutters do influence it a bit so might consider investigating if those can be disabled. I am just about ready to put the truck back into service on longer range trips again now that I have somewhat regained trust as it seemed even doing fluid once a year and taking care of it was never enough given how poorly designed the thermal bypass valve seems was designed to let it get hot with almost no margins for the conditions most of us use our trucks for. Hope everything goes well for your vehicle and that you don't (knock on wood) face what I ran into.