10 speed Transmission Hot - Please help

truckguy82 · August 29

Was randomly browsing this topic. Haven’t posted in years. I was one of the first people to have this issue about 9 years ago on my 2014 6.2L with the 6l80. I had to troubleshoot it myself. Same symptoms, temp just kept rising.

If you want to know if your trans thermostat is stuck, all you have to do is locate the lines to the trans cooler, you can follow the 2 lines off the trans.

If the thermostat is operating normally, both the supply and return to the cooler will be scolding hot, if the line is stuck closed (which I believe still allows a very small amount of flow) then the supply line to the cooler will be hot, and the return will be cool to the touch because your trans cooler will have cooled the fluid to ambient because the flow is so slow.

Cliff notes:

when trans is fully warmed up….

thermostat ok = trans fluid line return line from cooler is hot

Malfunction = return line is cool to the touch

for reference, the k2xx trucks trans thermostat didn’t open until 190 degrees. With the trans cooler functioning normally, I could drag race while towing 6k lbs and it never got above 205.

260+ is really high and I’d replace all that fluid.

Edited August 29 by truckguy82

ArthurW · September 12

On 8/29/2024 at 12:23 AM, truckguy82 said:

Was randomly browsing this topic. Haven’t posted in years. I was one of the first people to have this issue about 9 years ago on my 2014 6.2L with the 6l80. I had to troubleshoot it myself. Same symptoms, temp just kept rising.

If you want to know if your trans thermostat is stuck, all you have to do is locate the lines to the trans cooler, you can follow the 2 lines off the trans.

If the thermostat is operating normally, both the supply and return to the cooler will be scolding hot, if the line is stuck closed (which I believe still allows a very small amount of flow) then the supply line to the cooler will be hot, and the return will be cool to the touch because your trans cooler will have cooled the fluid to ambient because the flow is so slow.

Cliff notes:

when trans is fully warmed up….

thermostat ok = trans fluid line return line from cooler is hot

Malfunction = return line is cool to the touch

for reference, the k2xx trucks trans thermostat didn’t open until 190 degrees. With the trans cooler functioning normally, I could drag race while towing 6k lbs and it never got above 205.

260+ is really high and I’d replace all that fluid.

Little delayed in getting back to you - but thank you for the information.

I will double check this next time I have the truck hot. For reference - it would be fairly easy for me to overheat my transmission if I was to "drag race" my truck while towing. I watch these videos of people towing, putting the pedal to the floor while climbing a mountain to see how it holds speed, etc. My truck's transmission would overheat in 10 minutes if I did that lol.

I have a shutter now while driving at highway speeds, (kind of intermittently) and a few real weird shifts/flares at times. Unfortunately all of these issues are very intermittent, and I know my dealer would "not able to replicate" it lol.

Ejl923 · September 12

Had my first real tow with my 24 5.3/ 10 spd Silverado. Towed my 4000 lb camper 340 miles, mid August. Temp didn’t get much above 170 the entire trip. Other than a malfunctioning part, wonder if there were any changes between the two years?

truckguy82 · Friday at 08:29 PM

On 9/12/2024 at 3:17 PM, ArthurW said:

Little delayed in getting back to you - but thank you for the information.

I will double check this next time I have the truck hot. For reference - it would be fairly easy for me to overheat my transmission if I was to "drag race" my truck while towing. I watch these videos of people towing, putting the pedal to the floor while climbing a mountain to see how it holds speed, etc. My truck's transmission would overheat in 10 minutes if I did that lol.

I have a shutter now while driving at highway speeds, (kind of intermittently) and a few real weird shifts/flares at times. Unfortunately all of these issues are very intermittent, and I know my dealer would "not able to replicate" it lol.

Yeah mine would get to 230 degrees just not towing anything.

It literally was just a slow and gradual rise up to temp like it’s supposed to, but it just didn’t stop rising. Exactly what would happen if you didn’t have a functioning trans cooler because the flow was blocked.

Back when I had a problem with mine, the dealer could not figure it out and nobody had ever had this problem before. Had to diagnose on my own. It seems relatively common now. I bet 75% of people don’t even look at their trans temp and most would have no idea.

I’d just remove the thermostat if you can. Our was at 190 degrees so I didn’t remove mine because I didn’t think it was wise to run at like 60 degrees less than design temp in the winter. But now that you guys have a 150-160 degree stat, it proves that 190 is BS…I would just remove it. In the case of the 6l80, it was just called “flipping the pill” which was basically just making sure the thermostat was always open. Thermostat was external though. Not sure how easy it is on the 10speed’s.

Edited Friday at 08:34 PM by truckguy82