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

Another JR · October 19, 2022

5 hours ago, Grumpy Bear said:

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

Thanks. That’s good to know. Looks like the part and seals are around $80.

I decided to call GM and open a warranty case to get their position on the intent of 21-NA-199 as it applies to my case (complained of occasional rough 2-1 shift, no fault found). I figure it’s worth a shot trying to get them to cover it. The person said they’d call me with an answer tomorrow.

mrjulian416 · December 6, 2022

Took my '21 in for a free tire rotation and "after blow" activation. While they had it I mentioned some hard 2-1 downshifts and asked for the TSB to be applied. Service writer made no arguments and said they'd take care of it.

Of course it took two trips since the first trip only confirmed I didn't have the 70C housing so "they had to order it". Two weeks later and another day at the dealer and I now have the lower temp t-stat.

Can confirm steady state highway transmission temps are now about 154F vs. the previous 195F.

Pryme · December 6, 2022

1 hour ago, mrjulian416 said:

Took my '21 in for a free tire rotation and "after blow" activation. While they had it I mentioned some hard 2-1 downshifts and asked for the TSB to be applied. Service writer made no arguments and said they'd take care of it.

Of course it took two trips since the first trip only confirmed I didn't have the 70C housing so "they had to order it". Two weeks later and another day at the dealer and I now have the lower temp t-stat.

Can confirm steady state highway transmission temps are now about 154F vs. the previous 195F.

What is afterblow activation?

mrjulian416 · December 6, 2022

27 minutes ago, Pryme said:

What is afterblow activation?

Afterblow turns on the cabin air fan if you've been using AC when you turn off the truck to dry the evaporator coil and prevent mold/mildew buildup. It requires the dealer scan tool, and some dealers will do it for free while servicing your vehicle... some will want to charge 0.5hrs. Mine did it for free. Per GM:

"Afterblow is a feature that dries the evaporator core by operating the blower motor after the engine is turned off. This reduces the amount of microbial growth that can create undesirable odors. The vehicle does not come equipped with the afterblow feature turned on. If the afterblow feature is required due to an odor concern, it must be turned on by reprogramming the HVAC control module, refer to Service Programming System (SPS) (See: Programming and Relearning) .

After the HVAC control module has been programmed for afterblow, the following conditions must be met for afterblow to operate:

The engine has been turned off for at least 32 minutes.
The ambient air temperature is at least 21°C (70°F).
The A/C compressor operated for more than 2 minutes.
The system voltage is at least 12 volts.

Once the above conditions have been met, the following sequence of events will occur:

The blower motor will run for 20 seconds.
The blower motor will be off for 10 minutes.
The blower motor will run for and additional 20 seconds"

Pryme · December 7, 2022

5 hours ago, mrjulian416 said:

Afterblow turns on the cabin air fan if you've been using AC when you turn off the truck to dry the evaporator coil and prevent mold/mildew buildup. It requires the dealer scan tool, and some dealers will do it for free while servicing your vehicle... some will want to charge 0.5hrs. Mine did it for free. Per GM:

"Afterblow is a feature that dries the evaporator core by operating the blower motor after the engine is turned off. This reduces the amount of microbial growth that can create undesirable odors. The vehicle does not come equipped with the afterblow feature turned on. If the afterblow feature is required due to an odor concern, it must be turned on by reprogramming the HVAC control module, refer to Service Programming System (SPS) (See: Programming and Relearning) .

After the HVAC control module has been programmed for afterblow, the following conditions must be met for afterblow to operate:

The engine has been turned off for at least 32 minutes.
The ambient air temperature is at least 21°C (70°F).
The A/C compressor operated for more than 2 minutes.
The system voltage is at least 12 volts.

Once the above conditions have been met, the following sequence of events will occur:

The blower motor will run for 20 seconds.
The blower motor will be off for 10 minutes.
The blower motor will run for and additional 20 seconds"

That was a fantastic explanation, thanks. I’ve never heard of that on any vehicle I’ve owned. Have you done it with other vehicles too?

anyone else do this with their HD?

Another JR · December 7, 2022

It’s frustrating that the dealers are inconsistent on doing the thermostat sb. Mine wouldn’t do it and the GM tech support/warranty people backed them up and said no.

Edited December 7, 2022 by Another JR

mrjulian416 · December 7, 2022

13 hours ago, Pryme said:

That was a fantastic explanation, thanks. I’ve never heard of that on any vehicle I’ve owned. Have you done it with other vehicles too?

anyone else do this with their HD?

I have never done it before... this is my first vehicle that actually has the capability. Living in NC, I figure it can't hurt.

12 hours ago, Another JR said:

It’s frustrating that the dealers are inconsistent on doing the thermostat sb. Mine wouldn’t do it and the GM tech support/warranty people backed them up and said no.

That is more than frustrating, it's wrong. The TSB plainly says even if the dealer can't reproduce the complaint, the TSB should be applied. I'd try another dealer before making the swap myself. At the very least have a conversation with the Service manager and/or the dealer general manager.

Jettech1 · December 18, 2022

This is kind of a confusing topic for me. With our 2022 custom model crew cab gasser picked up our new 8k lb. camper in mid September in Jacksonville, FL. I towed it 255 miles to Byron, GA in 95' heat running at 65mph. Trans never went above 182. Today I towed our camper from Byron, GA to Goodwater, AL. Trans never went above 170. It was 45' out, super cold for us but I've never seen it above 182 in very high heat and lots of hills...Is it safe to assume this was an earlier model problem?

Edited December 18, 2022 by Jettech1

Another JR · December 18, 2022

My 2021 was built in the March/April timeframe in 2021. They switched to the lower temp thermostat a month or two after that. Your 2022 has the lower temp thermostat.

Jettech1 · December 18, 2022

45 minutes ago, Another JR said:

My 2021 was built in the March/April timeframe in 2021. They switched to the lower temp thermostat a month or two after that. Your 2022 has the lower temp thermostat.

Thank you, I appreciate your reply.

Another JR · December 18, 2022

No problem. Here is a link to the service bulletin describing the issue and showing what’s affected.

https://static.nhtsa.gov/odi/tsbs/2021/MC-10207911-9999.pdf

Jettech1 · December 18, 2022

1 hour ago, Another JR said:

No problem. Here is a link to the service bulletin describing the issue and showing what’s affected.

https://static.nhtsa.gov/odi/tsbs/2021/MC-10207911-9999.pdf

Interesting, thank you!

64BAwagon · December 18, 2022

My Dec 2020 built truck has a "flare" when downshifting from 6 to 5 while pulling the fifth wheel. I normally dont let it get to 6th gear since 5th is a better RPM range for the speed I typically run (63-64 MPH)

I wasnt going to take it in for this issue since I would get the whole run around about not being able to duplicate (it has only done it while pulling this trailer) and I didnt want to have a half tank of gas wasted screwing around with it. After seeing this TSB

I will likely have it done in the spring, no reason to take it out and get it all salty right now.

Jettech1 · December 18, 2022

3 hours ago, 64BAwagon said:

My Dec 2020 built truck has a "flare" when downshifting from 6 to 5 while pulling the fifth wheel. I normally dont let it get to 6th gear since 5th is a better RPM range for the speed I typically run (63-64 MPH)

I wasnt going to take it in for this issue since I would get the whole run around about not being able to duplicate (it has only done it while pulling this trailer) and I didnt want to have a half tank of gas wasted screwing around with it. After seeing this TSB

I will likely have it done in the spring, no reason to take it out and get it all salty right now.

If you use tow/haul mode 6th should be locked out already. Are you using that mode? If not, towing a 5th wheel that I'm guessing weighs quite a bit could be all of your problem. Try tow/haul mode. Hopefully problem solved.

Edited December 18, 2022 by Jettech1

Pryme · December 18, 2022

My truck was built in July of 22 and must have the lower thermostat as my transmission temp unloaded over 600mi drive this weekend hung between 147-151