8L90 Transmission Operating Temperature

TruckinCountry · March 23, 2023

I have a 2016 Chevrolet Silverado V8 5.3 pickup with the 8L90 transmission. What operating temperature should I be running? Just looking for feedback on standard operating temperature for daily driving with no load. Any feedback regarding transmission operating temperature is greatly appreciated. Would like to hear from some who run the 8L90 as well.

Background: I got a transmission shop trying to tell me that 120*F and under is normal operating temperature for a transmission with the bypass valve. Not buying it, so just gathering some information to back me up to provide when I pay them another visit. Feel free to provide your feedback on that claim as well.

Edited March 23, 2023 by TruckinCountry
Add fahrenheit, fix spelling

rav3 · March 23, 2023

Interesting question. Check out this updated TSB from GM about changing the transmission thermostat from 90C (194f) to 70C (158f). with that said, what is normal?

The old 4 speed transmission didn't have a transmission thermostat at all. to get more MPG, GM decided to heat up the transmission fluid to make the fluid thinner. So they added a 90c thermostat on your transmission. Then the transmissions/torque converters started failing, so now the have a TB to install a lower 70c thermostat.

Most experts will tell you that the worst thing to kill a transmission is HEAT. I did the "pill flip" on my 6L90 & mine runs between 115 to 150, depending on ambient temps, even driving in our mountains in WNC.

In my opinion, what you guy told you is pretty correct, when not towing or hot rodding.

If I were you, I'd do the pill flip or there's a kit out there to modify the thermostat to stay open & fluid will run just like all the earlier truck transmission.

Hope this helps

21-NA-199 1..3 (nhtsa.gov)

newdude · March 23, 2023

2 hours ago, rav3 said:

Interesting question. Check out this updated TSB from GM about changing the transmission thermostat from 90C (194f) to 70C (158f). with that said, what is normal?

The old 4 speed transmission didn't have a transmission thermostat at all. to get more MPG, GM decided to heat up the transmission fluid to make the fluid thinner. So they added a 90c thermostat on your transmission. Then the transmissions/torque converters started failing, so now the have a TB to install a lower 70c thermostat.

Most experts will tell you that the worst thing to kill a transmission is HEAT. I did the "pill flip" on my 6L90 & mine runs between 115 to 150, depending on ambient temps, even driving in our mountains in WNC.

In my opinion, what you guy told you is pretty correct, when not towing or hot rodding.

If I were you, I'd do the pill flip or there's a kit out there to modify the thermostat to stay open & fluid will run just like all the earlier truck transmission.

Hope this helps

21-NA-199 1..3 (nhtsa.gov)

This is for 6 speed, not 8 speed.

newdude · March 23, 2023

2 hours ago, TruckinCountry said:

I have a 2016 Chevrolet Silverado V8 5.3 pickup with the 8L90 transmission. What operating temperature should I be running? Just looking for feedback on standard operating temperature for daily driving with no load. Any feedback regarding transmission operating temperature is greatly appreciated. Would like to hear from some who run the 8L90 as well.

Background: I got a transmission shop trying to tell me that 120* and under is normal operating temperature for a transmission with the bypass valve. Not buying it, so just gathering some information to back me up to provide when I pay them another visit. Fell free to provide your feedback on that claim as well.

8L90 on 15-18 trucks the stock TBV is full open at 194F.

If the pill has been flipped or the SureCool aftermarket TBV bypass was installed, you'd see 100-130F.

Edited March 23, 2023 by newdude

ForestryGuy · January 11, 2025

Resurrecting this thread to get some answers or reassurance that I made the right choice by installing the Shift Technology STL010 kit on my 8l90. The truck is a 2018 Sierra with 103K miles.

I live in southern CO, it gets cold here but also gets hot in the summer. I do a lot of driving up mountain passes and towing a 6k pound camper. Driving up to the ski area Ive been seeing temps in the 190s and occasionally getting burning smell. Trans fluid and filter were recently changed at 90k by the dealer. Had them check it out recently and they said everything is good. No shudder no hard shifts - I think it drives pretty good for a truck with just over 103k miles.

We've got a trip planned for spring break where we will be towing a camper across the southwest so this afternoon I installed the Shift Technology kit to keep my temps lower and hopefully keep the trans happy for the remainder of my time with the truck. I'd keep it to 200K or more if it will make it.

Driving home after the install 28F outside temps and I am seeing trans temps 103-108F. Is this too cold? Shifts were a little more noticeable but not harsh.

I am worried this is too cold for the trans - I don't want to create a problem but solve a potential one.

Thanks!

CamGTP · January 11, 2025

Those temps are fine if the truck isn't being pushed. If you started being more aggressive with your driving the temps would come up. My 6 speeds runs between 110-125 in the cold months if I drive it. Stays around 145-150 in the summer with no load. Pull a trailer and it starts to rise a little but still way cooler than the factory thermostat temp that it came with, which helps with fluid life.

ForestryGuy · January 11, 2025

Thanks for that info. This was a chill drive home with no aggressive driving. I’ll be driving up to the ski area tomorrow so I’m hoping this prevents the burning smell.