10 speed Transmission Hot - Please help

truckguy82 · August 29, 2024

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, 2024 by truckguy82

ArthurW · September 12, 2024

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, 2024

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 · September 13, 2024

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 September 13, 2024 by truckguy82

TheRiver · September 15, 2024

Can't hardly believe the OP has put up with this for a YEAR now!!!!!!!

ArthurW · October 10, 2024

On 9/13/2024 at 5:29 PM, truckguy82 said:

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.

Unfortunately it is part of the valve body on the 10 speeds with the gas application. Probably explains the reluctance on GM's part to do anything to help me.

I have very similar symptoms to what you had though. Temperature just continuously goes up, never comes down.

On 9/15/2024 at 5:55 AM, TheRiver said:

Can't hardly believe the OP has put up with this for a YEAR now!!!!!!!

I've basically given up on it at this point. After 12 visits to the dealer, countless headaches, phone calls with GM Support Canada, and countless emails, a meeting with the general manager of my local dealer, a meeting with a service manager at another dealer, I have literally gotten NOWHERE.

I really like GM's trucks otherwise, but the dealers around me aren't willing to do anything to help me. I've just come to the conclusion that I will trade the truck in when it makes sense financially, and never come back to GM again because of this whole ordeal. I don't even care that the truck has issues, the problem I have is that it's been a ridiculous headache trying to get some layer of service to help me with the issue. I won't buy another GM. From my experience where I live, and with the lack of support on my local dealer's, and GM Canada's part there is no way I can risk having to go through this again with another vehicle.

It is what it is, but it's a shame that someone who's been an avid GM guy for years has just been let down this heavily. This issue will affect my families purchases, and most of my social and professional work environments purchases moving forward who all know about the issues I've had. All over a call it maximum $5000.00 repair.

Edited October 10, 2024 by ArthurW

TrueBlue · October 10, 2024

Personally Arthur, I don't understand GM's position on this. That $5K repair might have equaled the profit they made on the truck. Maybe. But even if it did it would have been a wash. Now they're getting to keep their profit on this one rig, and lose many potential sales and profits on other vehicles as a result. I'm not a businessman but I don't see how that equates to sustainability of their bottom line.

truckguy82 · October 11, 2024

On 10/10/2024 at 9:32 AM, ArthurW said:

Unfortunately it is part of the valve body on the 10 speeds with the gas application. Probably explains the reluctance on GM's part to do anything to help me.

I have very similar symptoms to what you had though. Temperature just continuously goes up, never comes down.

I've basically given up on it at this point. After 12 visits to the dealer, countless headaches, phone calls with GM Support Canada, and countless emails, a meeting with the general manager of my local dealer, a meeting with a service manager at another dealer, I have literally gotten NOWHERE.

I really like GM's trucks otherwise, but the dealers around me aren't willing to do anything to help me. I've just come to the conclusion that I will trade the truck in when it makes sense financially, and never come back to GM again because of this whole ordeal. I don't even care that the truck has issues, the problem I have is that it's been a ridiculous headache trying to get some layer of service to help me with the issue. I won't buy another GM. From my experience where I live, and with the lack of support on my local dealer's, and GM Canada's part there is no way I can risk having to go through this again with another vehicle.

It is what it is, but it's a shame that someone who's been an avid GM guy for years has just been let down this heavily. This issue will affect my families purchases, and most of my social and professional work environments purchases moving forward who all know about the issues I've had. All over a call it maximum $5000.00 repair.

Here’s how you can prove it and what I would do.

Get a laser thermometer off amazon or home depot, cheap one, take a video, upload it to youtube so you can easily share it. In the video, show the trans temp on the dash, and then show the temp of both of the external trans cooler lines with the laser thermometer.

If your thermostat is like the 6l80’s, it will still allow for 5-10% flow. That means the line to the trans cooler will be scorching hot. Because the flow is so slow the output line of the trans cooler will get cooled down to ambient. If it’s zero flow both lines will be cool.

This is undeniable evidence that you don’t actually have a problem with your trans and that you just don’t have any trans cooler flow.

If you want you can email it to me and I can throw it on my youtube. I use youtube just to easily store and share personal videos.

Edited October 11, 2024 by truckguy82

ArthurW · October 13, 2024

On 10/11/2024 at 10:34 AM, truckguy82 said:

Here’s how you can prove it and what I would do.

Get a laser thermometer off amazon or home depot, cheap one, take a video, upload it to youtube so you can easily share it. In the video, show the trans temp on the dash, and then show the temp of both of the external trans cooler lines with the laser thermometer.

If your thermostat is like the 6l80’s, it will still allow for 5-10% flow. That means the line to the trans cooler will be scorching hot. Because the flow is so slow the output line of the trans cooler will get cooled down to ambient. If it’s zero flow both lines will be cool.

This is undeniable evidence that you don’t actually have a problem with your trans and that you just don’t have any trans cooler flow.

If you want you can email it to me and I can throw it on my youtube. I use youtube just to easily store and share personal videos.

On 5/26/2024 at 1:55 PM, ArthurW said:

I have some videos of the same process, both in front of the truck at the cooler and also underneath.

Been down this road unfortunately.

truckguy82 · October 13, 2024

3 hours ago, ArthurW said:

I have some videos of the same process, both in front of the truck at the cooler and also underneath.

Been down this road unfortunately.

Was that with the trans hot?

really depends where you measured. Most accurate place is the lines.

But yeah, looks like it’s definitely not working. Wish i could help.

Edited October 13, 2024 by truckguy82

ArthurW · October 13, 2024

2 hours ago, truckguy82 said:

Was that with the trans hot?

really depends where you measured. Most accurate place is the lines.

But yeah, looks like it’s definitely not working. Wish i could help.

Yeah that was with the transmission over 100c I believe. I have a video showing all the temps, pan was like 119 I think, lines near pan were 90s, and lines near cooler were 30 and 20

jasonr83 · January 5, 2025

Has your problem been resolved yet with trans overheating? I am a GM technician. I just stumbled upon this post. I'm very familiar with that transmission. I drive a 22 Sierra At4 with a 10spd as well.

ArthurW · January 15, 2025

On 1/5/2025 at 12:31 AM, jasonr83 said:

Has your problem been resolved yet with trans overheating? I am a GM technician. I just stumbled upon this post. I'm very familiar with that transmission. I drive a 22 Sierra At4 with a 10spd as well.

Hi Jason!

Absolutely not - I've not received any help, nor have I resolved this issue. I'd love to speak to someone who has some experience with this transmission to help out, or at least give me some ideas.

Anything you can provide would be a great benefit to me!

Thanks,
Arthur

redwngr · January 17, 2025

On 9/15/2023 at 9:02 AM, ArthurW said:

Hey all,

Looking for some input on my truck. It's a 2022 Sierra 5.3 with the 10 speed transmission. It has about 3000KM (around 2000 miles) on it. When I was towing my trailer the other weekend (about 5000lbs) the transmission got to 257F (125C) within about an hour of towing. I pulled over to let the transmission cool, because it continuously was rising. I was not working the truck very hard at all, allowing it to slow on the hills, etc. The ambient temperature was about 80F.

I took it to the dealer, and they told me this is completely normal for these trucks, and that it didn't set a code. I got them to put it in writing, but I really don't want to cause additional damage. I've never owned a truck that allowed the transmission to get this hot.

Is there anyone that has some specific information on this? I read the TSB about the twisted cooler line, but my dealer didn't even consider it an option.

Would love some help with this or at least some comparisons in terms of transmission temperatures, options, etc.

Arthur

How fast were you running when this was going on?

Was it steady speed?

What's temp does it get to when running highway without the trailer?

Approximate dimensions and weight of trailer?

ArthurW · January 17, 2025

26 minutes ago, redwngr said:

How fast were you running when this was going on?

Was it steady speed?

What's temp does it get to when running highway without the trailer?

Approximate dimensions and weight of trailer?

Hi.

- I was running about 55-62MPH (90-100KMH)
- Steady-ish speed, I let it slow down on hills (fairly flat province though, we're talking small grades, not mountains or anything like that).
- I don't really run much highway, most of my drive time without the trailer is approximately a 15-20 minute trip to/from work. Each way I normally hit anywhere from 180-200F during the summer. In the winter it's cooler, as right now it's pretty cold here. I haven't looked at the temperature recently, as usually in the winter I'm not towing nor do I notice any temperature problems.

- Camper is a older Prowler 25LX which has a base weight of about 4500-5000lbs. I don't haul it with the tanks full, ever, and our gear in the camper is fairly minimal, but probably an extra 500-1000lbs to be safe. It's 25ft long, typical camper trailer. No slides or anything like that. Truck doesn't struggle much at all power-wise towing it (well it does compared to my old Duramax, but not the same animal lol) and I don't push the truck hard. I'm never in a rush.

- EDIT: Also for reference, it also runs pretty stinkin' hot just hauling my utility trailer around with a couple walk behind mowers on it. Probably 3000lbs gross. Just toodlin' around the city I'll easily see transmission temperatures of 240+.

EDIT 2: I should also mention, I'm from a rural area in Canada. When I say "city" we're talking a population of 70,000 or so. No traffic, or anything like that. Just slower speeds.

Edited January 17, 2025 by ArthurW