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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

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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

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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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KARNUT Senior Enthusiast

KARNUT

Posted
Posted
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 Senior Enthusiast

64BAwagon

Posted
Posted
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. 

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Jettech1 Senior Enthusiast

Jettech1

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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.

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Pryme Senior Enthusiast

Pryme

Posted
Posted (edited)
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 by Pryme
Jettech1 Senior Enthusiast

Jettech1

Posted
Posted
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 Senior Enthusiast

Pryme

Posted
Posted
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 Senior Enthusiast

Jettech1

Posted
Posted
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 Senior Enthusiast

Pryme

Posted
Posted
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 Senior Enthusiast

Jettech1

Posted
Posted
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 Senior Enthusiast

Pryme

Posted
Posted
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. 

  • Haha 1
lsttype Enthusiast

lsttype

Posted
Posted

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 Senior Enthusiast

Jettech1

Posted
Posted
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..

  • Haha 2
Another JR Senior Enthusiast

Another JR

Posted
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Posted
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?

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