Transmission Thermal Bypass Valve

[UsualSuspect]

Having owned more GM vehicles over the years than most, I thought GM was using the updated TBV on all transmissions, but I just found out that GM is still using the older version if the engine is an LM2 and LM0.
The TBV is basically a thermostat for the transmission, when the fluid temperature reaches x, the valve opens and allows coolant to flow through the transmission cooler.
The original TBV that was used on almost all GM vehicles with 6L80, 6L90, opened at 194 degrees, and is mounted directly on the transmission. GM came out with an updated TBV 3 or 4 years ago, and a issued a TSB that advised to replace the TBV with the updated version that opens at 158 degrees due to transmission overheating.
Today I get a phone call, one of the 1500's is in the shop, needs a transmission, 10L80. The engine is a LM2, the truck is out of warranty, so it was transported from 900 miles away, to the company shop.
Shop mechanic tells me the TBV's in the LM0 and LM2's open at 194 degrees. The TBV on the gassers 10L80 open at 143 degrees. He is not sure why the higher temp on diesels, it's the same transmission in both.
He said the LM0 and LM2 TBV's are mounted on the frame, not directly on the side of the transmission, he isn't sure why the mounting is different, there is enough room for it. He said we had a 143 degree TBV on the shelf, it isn't under warranty, he doesn't think there will be any issues having the tranmission run cooler.
This is the first 10L80 failure, but it is reminescent of the 6L80 overheating, and I paid for enough 6L80 tranny's to own half the factory, I hope this is not a repeat.

 

[StephenPT]

I've done a little research on this topic and can't come up with a definitive reason why the gas engines use a lower TBV temp than the diesel other than that with the gas engine you will run the torque converter unlocked more often and since the torque converter builds a tremendous amount of heat when unlocked they run it at a lower operating temp so there's more "head room" between operating temp and peak temps when running the TC unlocked.

On the diesel the TC rarely ever unlocks and at most for a few seconds so they run it closer to the peak efficiency temp.

This is my guess as GM deliberately designed a different TBV for each platform.

FWIW - I never see temps above 200F - not even while towing. Road tripping with the family I'm usually in the 170's and while towing it's in the 180's, sometimes 190's.

Curious if by now you've heard back what the diagnosis was on the 10L80 that failed?