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Pros and Cons of Installing Later Transmission Thermostat with Lower Opening Temperature

Another JR

By Another JR
in 6.6L Gas V8 (L8T)

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Another JR Senior Enthusiast

Another JR

Posted
Posted

Hi All,

 

I have a 2021 GMC 3500HD CCLB SRW SLT gas delivered April 2021 with the older 195F setpoint transmission thermostat. I am typically carrying a 1800 lbs pop up slide in camper that is low drag (14 to 15 mpg with camper). The transmission temperature typically stabilizes between 187 and 195 in the mild PNW summer on long drives. The highest I’ve seen at the end of a climb was 200F, but I’ve not done any huge hot climbs yet. I’ve tried it towing 8000lbs but not on any long climbs that might challenge transmission cooling. 
 

I’m trying to decide whether to have the dealer do the free service bulletin replacement with the 150F thermostat even though I don’t seem to need it now. I have not done any heavy towing up long grades in hot weather, so I don’t know if there’s a cooling issue for my planned usage.  The most I’ll ever tow is about an 8000 lb boat/trailer.  No big travel trailer towing planned.  I assume if I wait until after my 3 year warranty is past it won’t be free. 
 

Are there any potential disadvantages to getting the lower temp thermostat other than the risk the dealer does something wrong (my experience is about 1 screwup for every 3 visits). Lower gas mileage?  I would do it at 15k miles and have the dealer do a transmission fluid and filter replacement at the same time.
 

Thanks 

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newdude
newdude

No cons, especially on an HD.  You will see a reduction in temps empty driving all day long.  Can it still build heat when towing?  Yes, but the fluid is flowing through the full cooling loop at a low

Grumpy Bear
Grumpy Bear

That is a flat out lie. Bolted the side of the transmission. Lord man, do it yourself. 

Another JR
Another JR

Yeah, that’s probably what I’ll do. I’m a bit concerned I’d have to add fluid, and the procedure for that may involve running the truck while adding fluid. (my BMW requires that). I’ll have to researc

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CamGTP Senior Enthusiast

CamGTP

Posted
Posted

Didn't know they put the thermostats on the 3/4 and 1 ton 6L90e transmission now, if they do.

 

You'd never regret running the transmission cooler. They never ran a thermostat when the transmission first came out and the cooler the fluid the better.

asilverblazer Senior Enthusiast

asilverblazer

Posted
Posted

I've lost maybe .5 - 1.5 mpg since 'flipping the pill' in mine, plus the transmission temperatures still get just as high as it did before, just takes a bit longer to get there.

newdude Senior Enthusiast

newdude

Posted
Posted (edited)
13 hours ago, Another JR said:

Hi All,

 

I have a 2021 GMC 3500HD CCLB SRW SLT gas delivered April 2021 with the older 195F setpoint transmission thermostat. I am typically carrying a 1800 lbs pop up slide in camper that is low drag (14 to 15 mpg with camper). The transmission temperature typically stabilizes between 187 and 195 in the mild PNW summer on long drives. The highest I’ve seen at the end of a climb was 200F, but I’ve not done any huge hot climbs yet. I’ve tried it towing 8000lbs but not on any long climbs that might challenge transmission cooling. 
 

I’m trying to decide whether to have the dealer do the free service bulletin replacement with the 150F thermostat even though I don’t seem to need it now. I have not done any heavy towing up long grades in hot weather, so I don’t know if there’s a cooling issue for my planned usage.  The most I’ll ever tow is about an 8000 lb boat/trailer.  No big travel trailer towing planned.  I assume if I wait until after my 3 year warranty is past it won’t be free. 
 

Are there any potential disadvantages to getting the lower temp thermostat other than the risk the dealer does something wrong (my experience is about 1 screwup for every 3 visits). Lower gas mileage?  I would do it at 15k miles and have the dealer do a transmission fluid and filter replacement at the same time.
 

Thanks 

 

 

No cons, especially on an HD.  You will see a reduction in temps empty driving all day long.  Can it still build heat when towing?  Yes, but the fluid is flowing through the full cooling loop at a lower temp right off the bat which will lower tow temps.  

 

Get it.  Tell the dealer you've experienced a shudder once or twice next time you take it for service.  GM wants the thermostat in there if its under warranty even for CCND (customer concern not duplicated).  21-NA-199 is the bulletin #.  

 

 

Edited by newdude
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  • 2 weeks later...
sheath Enthusiast

sheath

Posted
Posted

I like Newdude's response.  :cheers:

I can confirm that the trans temps can get hot under heavy load even with the new setup.  But having the temperature start being controlled at a lower temp would be helpful for the lower loads, like your camper and medium weight trailers. 

I'd have it done, but I'd inspect the work before leaving the dealership.  Walk into the service department with a pair of coveralls, a copy of the TSB and a tarp to lay on the ground.  Ask the Service Advisor to walk out to the truck with you, while you inspect the work.

Another JR Senior Enthusiast

Another JR

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1 hour ago, sheath said:

I like Newdude's response.  :cheers:

I can confirm that the trans temps can get hot under heavy load even with the new setup.  But having the temperature start being controlled at a lower temp would be helpful for the lower loads, like your camper and medium weight trailers. 

I'd have it done, but I'd inspect the work before leaving the dealership.  Walk into the service department with a pair of coveralls, a copy of the TSB and a tarp to lay on the ground.  Ask the Service Advisor to walk out to the truck with you, while you inspect the work.

Thanks for the responses everyone. 
 

Sheath:  Regarding checking their work at the dealer, is there a particular concern with errors they might make on this job?  I normally do a general under the hood and under the vehicle inspection at home after any dealer work. 

sheath Enthusiast

sheath

Posted
Posted

I doubt there is anything in particular, but humans make mistakes.  You had mentioned previous issues with this dealer.  So might as well check it before you leave.  Then you won't have to reschedule an appointment, if there is something done incorrectly.

Epsilon Plus Enthusiast

Epsilon Plus

Posted
Posted (edited)

You sure it has the old pill? My November 2021 built 22 has "70c" stamped on it. I thought all new 2020+ 6L90Es with thermos were the new 158F pills.

Edited by Epsilon Plus
Another JR Senior Enthusiast

Another JR

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10 hours ago, Epsilon Plus said:

You sure it has the old pill? My November 2021 built 22 has "70c" stamped on it. I thought all new 2020+ 6L90Es with thermos were the new 158F pills.

Hi. Yes I’m quite sure from the behavior, although I haven’t actually put eyes on the part number. My truck was built in early March 2021 and I took delivery in April. Driving unloaded it steadily works its way up to the 180-190F range and stabilizes, and will go up to 195F  or 196 on long climbs. 

  • 1 month later...
Another JR Senior Enthusiast

Another JR

Posted
  • Author
Posted

I took my truck to the dealer and asked them to do this TSB.  The service advisor said they can only cover it if there’s a related problem with the transmission. He read the stored codes - nothing transmission related. I told him the only thing i can complain about other than the high thermostat set point is the occasional rough 2-1 downshift approaching a stop uphill if I give it a little gas.
 

He offered to keep it overnight and do a road test over the temperature range starting cold, so I had them do that. He said they could not identify anything wrong to justify replacing the thermostat. (I agree - the transmission works great. ). 
 

He said the change involves dropping the transmission pan and replacing a harness inside that has a temperature sensor. That sounds different from what others have described here. For example, a person above mentions being able to see the part code externally. I had the impression it was a device in the external cooling circuit. Can anyone clarify what the work is to change out the thermostat?  Thanks

Grumpy Bear Senior Enthusiast

Grumpy Bear

Posted
Posted
3 hours ago, Another JR said:

He said the change involves dropping the transmission pan and replacing a harness inside that has a temperature sensor.

 

That is a flat out lie. Bolted the side of the transmission. Lord man, do it yourself. :banghead:

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Another JR Senior Enthusiast

Another JR

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14 hours ago, Grumpy Bear said:

 

That is a flat out lie. Bolted the side of the transmission. Lord man, do it yourself. :banghead:

Yeah, that’s probably what I’ll do. I’m a bit concerned I’d have to add fluid, and the procedure for that may involve running the truck while adding fluid. (my BMW requires that). I’ll have to research it.
 

His description of the work didn’t seem right, but I didn’t have the TSB printed and with me when I was there. I may print it and go back and ask WTF, and how am I supposed to trust them about anything now. 

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pokismoki Senior Enthusiast

pokismoki

Posted
Posted

i have a 2012 2500 HD  truck, and it has no thermostat back then.. with the factory giant trans cooler and pulling 8000lbs trailer up steep grade mountain passes at 55mph i can hit 190 degrees.  in the flats at 65mph it runs all day at 120-130 degrees

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Grumpy Bear Senior Enthusiast

Grumpy Bear

Posted
Posted
On 10/15/2022 at 1:28 PM, Another JR said:

Yeah, that’s probably what I’ll do. I’m a bit concerned I’d have to add fluid, and the procedure for that may involve running the truck while adding fluid. (my BMW requires that). I’ll have to research it.
 

His description of the work didn’t seem right, but I didn’t have the TSB printed and with me when I was there. I may print it and go back and ask WTF, and how am I supposed to trust them about anything now. 

 

You won't loose more than a shot glass full. 😉 

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