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

Another JR · December 21, 2022

3 hours ago, KARNUT said:

Well it’s manual mode with the added feature. If you put it second gear and it hits the rev limit. It’s in manual mode.

Hi Karnut. Could you explain a little more? I know that if you select an L level that would cause exceedance of a rev limit it won’t downshift, but are you talking about an additional feature or behavior? Thanks

KARNUT · December 21, 2022

10 minutes ago, Another JR said:

Hi Karnut. Could you explain a little more? I know that if you select an L level that would cause exceedance of a rev limit it won’t downshift, but are you talking about an additional feature or behavior? Thanks

Hello. My last new truck had manual mode. It would shift up to the last gear you selected. Before I got a tune and eliminated cylinder deactivation it was M5. It also had rev matching if I downshifted. It would hold that gear if I desired.

64BAwagon · December 21, 2022

18 hours ago, Another JR said:

Correct. It’s not a manual mode. It is a selectable top gear mode. The transmission will shift normally except it won’t upshift beyond your selection. It can be used in normal or tow/haul mode.

Thats helpful info, too bad the owners manual doesnt explain that. I found that by running under 65mph the truck rarely will try to shift into 6th unless theres a pretty good downgrade. Over 65 it will upshift more often when on flat ground with a favorable wind. I will just leave mine in 5th from now on. I will check on the programming for 6th lockout, maybe they can do that when they do the thermostat TSB.

Jettech1 · December 29, 2022

On 12/21/2022 at 5:52 PM, 64BAwagon said:

Thats helpful info, too bad the owners manual doesnt explain that. I found that by running under 65mph the truck rarely will try to shift into 6th unless theres a pretty good downgrade. Over 65 it will upshift more often when on flat ground with a favorable wind. I will just leave mine in 5th from now on. I will check on the programming for 6th lockout, maybe they can do that when they do the thermostat TSB.

I tried this out today unloaded, locked it into 5th gear. Came to a stop, truck downshifted like normal, started off in first gear and upshifted normally until it got to 5th gear, then stayed there. So the update I have that locks out 6th gear when in TH mode doesn't change a thing when using the L mode. Good stuff here.

lsttype · March 4, 2023

On Dodges we call it a thermal bypass. Just get rid of the thermostat and enjoy cooler trans temps

Pryme · March 5, 2023

On 12/29/2022 at 12:01 AM, Jettech1 said:

I tried this out today unloaded, locked it into 5th gear. Came to a stop, truck downshifted like normal, started off in first gear and upshifted normally until it got to 5th gear, then stayed there. So the update I have that locks out 6th gear when in TH mode doesn't change a thing when using the L mode. Good stuff here.

So I just finished up a 750mi road-trip and pulled back a 6x12 uhaul trailer loaded up. Not really heavy but I got to use the truck to tow with. About 3500lbs. I used tow haul. Mine goes into 6th often but not as readily as without a trailer(no tow haul on)

6th with cruise set at 65 is 1,675rpm. When it shifts to 5th it’s at 2,100.

also for the heck of it I noticed my oil life went down 3% towing about 400mi.

Also hit 100 engine hours at 3,668 miles.

3500lbs was not enough to do anything to this trucks temps. 147-151 trans whole trip.

Edited March 5, 2023 by Pryme

Jettech1 · March 5, 2023

18 hours ago, Pryme said:

So I just finished up a 750mi road-trip and pulled back a 6x12 uhaul trailer loaded up. Not really heavy but I got to use the truck to tow with. About 3500lbs. I used tow haul. Mine goes into 6th often but not as readily as without a trailer(no tow haul on)

6th with cruise set at 65 is 1,675rpm. When it shifts to 5th it’s at 2,100.

also for the heck of it I noticed my oil life went down 3% towing about 400mi.

Also hit 100 engine hours at 3,668 miles.

3500lbs was not enough to do anything to this trucks temps. 147-151 trans whole trip.

I don't get why your truck is going into 6th gear when in TH mode. And mine doesn't. My build date is 07/2022. What is yours?

Pryme · March 6, 2023

5 hours ago, Jettech1 said:

I don't get why your truck is going into 6th gear when in TH mode. And mine doesn't. My build date is 07/2022. What is yours?

Same. In flint. Our trucks might have been next to each other in the line.

I was only towing 3500-3800lbs though. But it was for sure dropping down into 6th plenty. It spent some time in 5th too though. And of course shifts into 4-3-2 and so on when you brake for stop lights etc.

Jettech1 · March 6, 2023

Just now, Pryme said:

Same. In flint. Our trucks might have been next to each other in the line.

I was only towing 3500-3800lbs though. But it was for sure dropping down into 6th plenty. It spent some time in 5th too though. And of course shifts into 4-3-2 and so on when you brake for stop lights etc.

This topic is so weird....how in the hell are our trucks so different? Programming should have been the same...I'm so confused here...

Pryme · March 6, 2023

42 minutes ago, Jettech1 said:

This topic is so weird....how in the hell are our trucks so different? Programming should have been the same...I'm so confused here...

Maybe ask if you can have them re flash it or whatever with a software update

Jettech1 · March 6, 2023

3 minutes ago, Pryme said:

Maybe ask if you can have them re flash it or whatever with a software update

I don't want my truck updated...I was concerned as to how the other trucks are so different.

Pryme · March 6, 2023

9 hours ago, Jettech1 said:

I don't want my truck updated...I was concerned as to how the other trucks are so different.

You already know you’re going to get a 2024 ha! I can sense it.

lsttype · March 8, 2023

Hey fellas, they sell bybass kits that just keep the thermo open always. Wouldnt that and a deep aluminum pan be a great way to keep the temps on the low side? Thats what I did on my ram and the temps were alway low. Like 165 was the highest towing 9k.

Jettech1 · March 9, 2023

On 3/6/2023 at 8:20 AM, Pryme said:

You already know you’re going to get a 2024 ha! I can sense it.

Knock it off young man....lol....No I'm not!!! But damn it would be nice....oh stop planting seeds in my brain. Everyone says I'm easy to read....perhaps I am....NO IM NOT GETTING A 2024.....I'm telling myself that right now...lol..

Another JR · March 11, 2023

On 3/8/2023 at 7:28 AM, lsttype said:

Hey fellas, they sell bybass kits that just keep the thermo open always. Wouldnt that and a deep aluminum pan be a great way to keep the temps on the low side? Thats what I did on my ram and the temps were alway low. Like 165 was the highest towing 9k.

I don’t think eliminating the thermostat is a good idea other than maybe for truck that is always operated in a hot environment. You want the operating temperature to warm up to a stable temperature and design around that.

I still am curious why GM engineers originally decided they wanted that nominal temperature up at 195F. Was it to improve fuel economy by having the ATF slightly less viscous? Another reason? They obviously later decided the 153F was a better compromise, but what was the thinking behind the original decision?

Anybody know or care to speculate?