Updated Thermal Bypass Valve Installed, still reaches 195 F

gmm43 · May 7

Just recently bought a 2018 Sierra 1500 4.3V6 with the 6L80, 91xxx miles. A week or so later I ordered my AFM disabler and the GM updated TBV. Normally my trans temps would be 190-210 city driving, 170-185 highway.. took a while for it to be delivered through snail mail but when it finally got here I went ahead and swapped it out. I noticed that the trans fluid would reach 180s about after 20 min or so of highway driving( its been high 80's here these past few days). It definitely takes longer for the fluid to reach these temps but I was expecting way cooler levels. After driving on highway for half an hour(185 F), I drove around town and parked at grocery store and watched the temp rise to around 193 F at idle, shopped for a few minutes and when I started the truck again it was down to 185 F and pretty much remained that temp for the 10 minute drive home stop and go traffic.

only one previous owner and had excellent service history on carfax, regular oil changes and one Transmission fluid change at 45k miles. I'm waiting on my filter. gasket and fluid to be delivered some time next two weeks to change out the fluid myself. Transmission runs fine to me .

any ideas why my trans temp is so high?? anyone else have a similar experience with the GM TBV update?

I should also mention the i went ahead and ordered the STL010 from Shift Tech, hopefully that continuous flow will give lower temps

Edited May 8 by gmm43

TheRiver · May 8

"Active Grill Shutters"???

rav3 · May 8

10 minutes ago, TheRiver said:

"Active Grill Shutters"???

That would throw a code.

gmm43 · May 8

1 minute ago, rav3 said:

That would throw a code.

No code thrown

rav3 · May 8

Your transmission thermostat change only drops the 'open temp' by about 20 degrees, IIRC. the pill flip or thermostat delete is a constant open & cooling of transmission fluid. I did the pill flip 3 years ago on my 17 & I don't usually see it above 140-145 F. It cools fluid like the older 4L80 transmission. This transmission thermostat is GMs way of trying to get more MPG due to EPA at the expense of the owner when torque converter goes bad & takes out the transmission. IMO

gmm43 · May 8

1 minute ago, rav3 said:

Your transmission thermostat change only drops the 'open temp' by about 20 degrees, IIRC. the pill flip or thermostat delete is a constant open & cooling of transmission fluid. I did the pill flip 3 years ago on my 17 & I don't usually see it above 140-145 F. It cools fluid like the older 4L80 transmission. This transmission thermostat is GMs way of trying to get more MPG due to EPA at the expense of the owner when torque converter goes bad & takes out the transmission. IMO

Wow really? honestly I chose the GM update only because of how easy it would be to just switch out the original one. But Im definitely going to install the STL010 kit I've got coming tomorrow. It basically keeps the the valves open to have the fluid go through the cooler all the time witch in turn is basically functioning as a delete. all I need is a pair of snap ring pliers ..
Thanks

rav3 · May 8

6 minutes ago, gmm43 said:

Wow really? honestly I chose the GM update only because of how easy it would be to just switch out the original one. But Im definitely going to install the STL010 kit I've got coming tomorrow. It basically keeps the the valves open to have the fluid go through the cooler all the time witch in turn is basically functioning as a delete. all I need is a pair of snap ring pliers ..
Thanks

In my opinion you won't be sorry. I'm not. My 6L80 is a weak transmission or maybe the factory torque converter. Lowering the transmission temperature along with frequent fluid changes may increase its life.

newdude · May 8

1 hour ago, gmm43 said:

Just recently bought a 2018 Sierra 1500 4.3V6 with the 6L80, 91xxx miles. A week or so later I ordered my AFM disabler and the GM updated TBV. Normally my trans temps would be 190-210 city driving, 170-185 highway.. took a while for it to be delivered through snail mail but when it finally got here I went ahead and swapped it out. I noticed that the trans fluid would reach 180s about after 20 min or so of highway driving( its been high 80's here these past few days). It definitely takes longer for the fluid to reach these temps but I was expecting way cooler levels. After driving on highway for half an hour(185 F), I drove around town and parked at grocery store and watched the temp rise to around 193 F at idle, shopped for a few minutes and when I started the truck again it was down to 185 F and pretty much remained that temp for the 10 minute drive home stop and go traffic.

only one previous owner and had excellent service history on carfax, regular oil changes and one Transmission fluid change at 45k miles. I'm waiting on my filter. gasket and fluid to be delivered some time next two weeks to change out the fluid myself. Transmission runs fine to me .

any ideas why my trans temp is so high?? anyone else have a similar experience with the GM TBV update?

I should also mention the i went ahead and ordered the STL010 from Shift Tech, hopefully that continuous flow will give lower temps

Its because you have the 4.3.

The 4.3 has the transmission cooler built into the right hand side tank of the radiator and that's it. The V8s of the same year as yours, they have one cooler that is out at the front in the top of the AC condenser and do not send any ATF through the radiator at all.

Here's the line routing for the 4.3. Out of the transmission, if I recall it should then be in flow to the bottom and then out from the top and then returns back to the transmission. Being it goes through the radiator only, the ATF is still being exposed to the coolant temp in the radiator itself so it maintains a higher temperature. A 2018 5.3 for example however would run 145-170F with the lower temp TBV. Mine ran no more than 170F on a hot day romping on it.

Your best bet to bring them down will be the SureCool bypass, but even then don't expect a larger drop. You might see 10 degrees lower or so, maybe 15. Your truck with the SureCool would operate temp wise like a 1999-2013 truck would as those all flowed through the radiator only on a V6 and V8s that did not have the heavy cooling, but even those that had heavy cooling (which had an aux cooler) still flowed through the radiator first.

Grumpy Bear · May 8

@newdude nailed it. To get a lower temp without additional cooler you need to lower the water temp. I run and IPSCO thermostat housing and a Reische Racing 170 F thermostat. Plus Red Line D6 fluid which has both a higher thermal capacity and thermal conductivity. Not sure they still sell that unit but STANT still sells a 180F that fits this holder and Katech started selling a 174 F unit that fits the stock housing. Yellow line is the one I'm currently on. 170 F water and 70 C TBV, Ancillary cooler is in the works.

Road speed is also a huge temperature driver both to fast and to slow.

Sitting parked or in town when there is no flow over the radiator and water temp rises well above the water thermostat set point will still drive temps up. The fix for that would be additional cooler with a separate thermostatically controlled fan.

gmm43 · May 8

21 hours ago, newdude said:

Its because you have the 4.3.

The 4.3 has the transmission cooler built into the right hand side tank of the radiator and that's it. The V8s of the same year as yours, they have one cooler that is out at the front in the top of the AC condenser and do not send any ATF through the radiator at all.

Here's the line routing for the 4.3. Out of the transmission, if I recall it should then be in flow to the bottom and then out from the top and then returns back to the transmission. Being it goes through the radiator only, the ATF is still being exposed to the coolant temp in the radiator itself so it maintains a higher temperature. A 2018 5.3 for example however would run 145-170F with the lower temp TBV. Mine ran no more than 170F on a hot day romping on it.

Your best bet to bring them down will be the SureCool bypass, but even then don't expect a larger drop. You might see 10 degrees lower or so, maybe 15. Your truck with the SureCool would operate temp wise like a 1999-2013 truck would as those all flowed through the radiator only on a V6 and V8s that did not have the heavy cooling, but even those that had heavy cooling (which had an aux cooler) still flowed through the radiator first.

Thanks for the diagram and explanation! will definitely install the Sure Cool

gmm43 · May 8

17 hours ago, Grumpy Bear said:

@newdude nailed it. To get a lower temp without additional cooler you need to lower the water temp. I run and IPSCO thermostat housing and a Reische Racing 170 F thermostat. Plus Red Line D6 fluid which has both a higher thermal capacity and thermal conductivity. Not sure they still sell that unit but STANT still sells a 180F that fits this holder and Katech started selling a 174 F unit that fits the stock housing. Yellow line is the one I'm currently on. 170 F water and 70 C TBV, Ancillary cooler is in the works.

Road speed is also a huge temperature driver both to fast and to slow.

Sitting parked or in town when there is no flow over the radiator and water temp rises well above the water thermostat set point will still drive temps up. The fix for that would be additional cooler with a separate thermostatically controlled fan.

very cool data! I guess for now my next step is an after market thermostat, after the Sure Cool mod. you would think that they would have the same tranny cooler on V6s as like the V8s since the V6s also come with towing package

newdude · May 9

1 hour ago, gmm43 said:

you would think that they would have the same tranny cooler on V6s as like the V8s since the V6s also come with towing package

Less towing capacity, less engine to cool. Even the older V6s didn't have a factory aux cooler.

Grumpy Bear · May 9

3 hours ago, gmm43 said:

very cool data! I guess for now my next step is an after market thermostat, after the Sure Cool mod. you would think that they would have the same tranny cooler on V6s as like the V8s since the V6s also come with towing package

I ran a "pill flip" before installing the 70C TBV. The blue and orange lines in the top graph. The 70 C TBV is a pretty comfortable 'floor' for temperature and has nearly zero impact on the hotter days. Sure Cool is like a pill flip and the insurance it provides is more smoke and mirrors than actual. If you plug that stacked plate exchanger in the cold tank you've already grenaded the transmission.

170 F on the water requires zero tuning. A 160 F stat however does. Too cool anyway.

Even if you faithfully duplicate my system you will still have days of high fluid temperatures. Stalled in traffic for example. Crawling for a hour on a hot day around a wreck on the I-80. Pulling heavy over a steep grade. Thing just needs more cooler to take the head off the snake. i.e. quicker cool down and more reserve. Just say'n.

gmm43 · May 10

21 hours ago, Grumpy Bear said:

If you plug that stacked plate exchanger in the cold tank you've already grenaded the transmission.

could you say that in layman's terms?

I just installed the SureCool today after work. truck was still warm by the time I finished, trans fluid temp read 187. I ran a test drive to the car wash going the scenic route. 10 min on the free way and plenty of stop and go city driving, letting her eat a couple of times.

Good news? It never hit 200...only went up to 199 and settled down to 194. I'll keep an eye on it in during the morning commute to see what happens when starts from ambient temp.