Silverado 6L80E Transmission Thermostat Delete

rav3 · July 30, 2020

Guys, I'm just curious about this delete. Can anyone chime in about the pros & cons for doing this? I currently have a '17 Silverado LTZ 5.3l with the 6 speed auto 6L80E & MAX tow package (which says it has enhanced cooling). Checking the transmission temp. on the dash display, it will get as high as approx. 190F. It make sense to me to run transmission fluid as cool as possible, that's why I'm asking. With the fluid line running thru the radiator (it does right?) it appears to me that it will heat it up when cold to at least the coolant temperature. When driving, even with the add'l transmission cooler, it can't get any cooler that the coolant temperature. Does that make sense? With the above modification, I assume that the fluid runs thru the cooler all the time, allowing it to be cooled & not restricted by the inline thermostat. In this way, the transmission & fluid runs cooler. Right? Is that a correct statement? I'm just trying to understand how it works.

Thanks for replies ....

bdbake01 · July 30, 2020

The transmission fluid does not go through the radiator. IF it has a cooler (not all do), it’s actually the top 5” or so of the AC condenser. And it is thermostatically controlled.

in my opinion, there is zero reason to modify this system. It seeeems hot, but that’s how it is designed to operate. Running cooler can get you into a variety of issues in certain situations, no improvements, and likely slightly lower mileage.

Grumpy Bear · July 30, 2020

1 hour ago, rav3 said:

Guys, I'm just curious about this delete. Can anyone chime in about the pros & cons for doing this? I currently have a '17 Silverado LTZ 5.3l with the 6 speed auto 6L80E & MAX tow package (which says it has enhanced cooling). Checking the transmission temp. on the dash display, it will get as high as approx. 190F. It make sense to me to run transmission fluid as cool as possible, that's why I'm asking. With the fluid line running thru the radiator (it does right?) it appears to me that it will heat it up when cold to at least the coolant temperature. When driving, even with the add'l transmission cooler, it can't get any cooler that the coolant temperature. Does that make sense? With the above modification, I assume that the fluid runs thru the cooler all the time, allowing it to be cooled & not restricted by the inline thermostat. In this way, the transmission & fluid runs cooler. Right? Is that a correct statement? I'm just trying to understand how it works.

Thanks for replies ....

Fluid leaves the transmission via the thermostats top line and is routed to the drivers side radiator tank (hot side on your model) then from there to the AC condensers top half and back to the thermostat. Some trucks go only to the radiator. The six cylinders like mine go to the passenger side tank (cold) and back to the thermostat.

Water heats faster than the trans fluid so in the beginning the radiator side works like a fluid heater or should if it had any flow at all but the GM thermostat does not have a minimum flow bypass and has a 192 ish F trigger temperature. So as is fluid is short circuited back to the transmission until enough work has been put into the fluid to get the pill in the thermostat off its seat after which it regulates to roughly 192 ish F. As the V8 models use the hot tank they get the extra cooler in the AC condenser for heavier work and by and large they run a bit warmer than the V6. About 20 degrees or so.

Flipping the pill will heat the fluid faster in the winter and keep it cooler year around UNTIL you ask more from the system than it can deliver. Steep long hill in Death valley at max GVWR sort of thing.

There isn't a transmission builder worth his wage that wouldn't tell you 180 F is plenty hot and staying under 175 F day in and day out will drastically length life of the unit. B&M, PATC, SONNAX, TransGo.

My 6L80E runs and shift as pretty as a peach with the pill flipped and a cooler water thermostat (bonus information) 123K trouble free miles. Red Line D6 fluid. Runs 130 ish winter and 160 summer. 170 F water thermostat. summer 180 winter.

JohnA ran a full series on this modification specific to the V8's a few years back. Great work and write up. He knows way more than I on that combination.

newdude · July 30, 2020

1 hour ago, rav3 said:

Guys, I'm just curious about this delete. Can anyone chime in about the pros & cons for doing this? I currently have a '17 Silverado LTZ 5.3l with the 6 speed auto 6L80E & MAX tow package (which says it has enhanced cooling). Checking the transmission temp. on the dash display, it will get as high as approx. 190F. It make sense to me to run transmission fluid as cool as possible, that's why I'm asking. With the fluid line running thru the radiator (it does right?) it appears to me that it will heat it up when cold to at least the coolant temperature. When driving, even with the add'l transmission cooler, it can't get any cooler that the coolant temperature. Does that make sense? With the above modification, I assume that the fluid runs thru the cooler all the time, allowing it to be cooled & not restricted by the inline thermostat. In this way, the transmission & fluid runs cooler. Right? Is that a correct statement? I'm just trying to understand how it works.

Thanks for replies ....

I just installed the Shift Technologies thermostat bypass kit. Temps are down 30-45F when it gets warmed up. It builds temperature no different than before so far.

1 hour ago, bdbake01 said:

The transmission fluid does not go through the radiator. IF it has a cooler (not all do), it’s actually the top 5” or so of the AC condenser. And it is thermostatically controlled.

in my opinion, there is zero reason to modify this system. It seeeems hot, but that’s how it is designed to operate. Running cooler can get you into a variety of issues in certain situations, no improvements, and likely slightly lower mileage.

It would operate no differently than a 2011-2019 Silverado HD gas truck. Those are open loop cooling at all times, no thermostat. Same with Colorado diesel trucks. They run at 130-150F no problems.

Your info on the cooler flow is correct on V8 trucks 2016-2018 and 2019 old body. On 2014-2015 V8, it ran through both the radiator and the condenser cooler, same on early build 8 speed 2016. V6 trucks run just through the radiator.

Edited July 30, 2020 by newdude

Grumpy Bear · July 30, 2020

https://globaltransmissionparts.com/6l80-6l90-sure-cool-cooler-flow-system-stl010/?gclid=EAIaIQobChMI7tbn8Nf16gIVCr3ACh3rSA61EAQYASABEgIcyPD_BwE

rav3 · July 30, 2020

23 minutes ago, Grumpy Bear said:

https://globaltransmissionparts.com/6l80-6l90-sure-cool-cooler-flow-system-stl010/?gclid=EAIaIQobChMI7tbn8Nf16gIVCr3ACh3rSA61EAQYASABEgIcyPD_BwE

@Grumpy Bear thanks for the link. I looked at it & wonder how does this device for $50 work any differently than just reversing the internals of the thermostat to by pass the unit? Looks like it has a spring loaded ball check valve. Just curious...

This video shows a simple way to "bypass" the transmission thermostat.

https://youtu.be/rYP6CMgfbwU

Edited July 30, 2020 by rav3

Grumpy Bear · July 30, 2020

1 hour ago, rav3 said:

@Grumpy Bear thanks for the link. I looked at it & wonder how does this device for $50 work any differently than just reversing the internals of the thermostat to by pass the unit? Looks like it has a spring loaded ball check valve. Just curious...

This video shows a simple way to "bypass" the transmission thermostat.

https://youtu.be/rYP6CMgfbwU

Yea, no clue. I did the pill flip and aligned the plug for best flow. Then added:

https://store.katechengines.com/174-degree-gen-5-lt-thermostat-p729.aspx

Gasket stays on this one. :crackup:

Runs as cool as the other side of the pillow.

rav3 · July 30, 2020

FYI, my truck is still under warranty. Will bypassing the transmission thermostat as discussed void it?

rav3 · July 30, 2020

2 hours ago, Grumpy Bear said:

Fluid leaves the transmission via the thermostats top line and is routed to the drivers side radiator tank (hot side on your model) then from there to the AC condensers top half and back to the thermostat. Some trucks go only to the radiator. The six cylinders like mine go to the passenger side tank (cold) and back to the thermostat.

Water heats faster than the trans fluid so in the beginning the radiator side works like a fluid heater or should if it had any flow at all but the GM thermostat does not have a minimum flow bypass and has a 192 ish F trigger temperature. So as is fluid is short circuited back to the transmission until enough work has been put into the fluid to get the pill in the thermostat off its seat after which it regulates to roughly 192 ish F. As the V8 models use the hot tank they get the extra cooler in the AC condenser for heavier work and by and large they run a bit warmer than the V6. About 20 degrees or so.

Flipping the pill will heat the fluid faster in the winter and keep it cooler year around UNTIL you ask more from the system than it can deliver. Steep long hill in Death valley at max GVWR sort of thing.

There isn't a transmission builder worth his wage that wouldn't tell you 180 F is plenty hot and staying under 175 F day in and day out will drastically length life of the unit. B&M, PATC, SONNAX, TransGo.

My 6L80E runs and shift as pretty as a peach with the pill flipped and a cooler water thermostat (bonus information) 123K trouble free miles. Red Line D6 fluid. Runs 130 ish winter and 160 summer. 170 F water thermostat. summer 180 winter.

JohnA ran a full series on this modification specific to the V8's a few years back. Great work and write up. He knows way more than I on that combination.

Can anyone give me the link to JohnA "full series on this mod"?

CamGTP · July 30, 2020

They would never know you did it, so it couldn't void anything.

For what it's worth, this is a great thing to do in my opinion. I went to the track last weekend with my truck, it was well over 85 degrees with +80% humidity, that nasty wet hot feeling. The drive there my temps got to 150ish on the open road, let my truck cool off while the track was getting ready. Once the lanes opened I got about 12 runs down the track in about 90 minutes, I hot lapped it back to back many times. It took 4-5 passes for me to even breach 190 degrees and all the runs after that the temps stayed under 196 just beating on it. I left the track and the temps still above 190, within 10 miles it was back down to 165. There is no way it would have ever done that with the thermostat still installed.

Grumpy Bear · July 31, 2020

4 hours ago, rav3 said:

FYI, my truck is still under warranty. Will bypassing the transmission thermostat as discussed void it?

I can't answer that without a fire fight I'm no longer willing to fight. That said....I'll give you my take.

I bought my truck and I own my truck and when it is all said and done I'm stuck with whatever decision I make. GM makes money now, not vehicles and they frankly don't care.

I know for a fact heat kills transmissions. I know for a fact GM runs them too hot to be reliable. I know they do it for mileage and I know that is BS. (I get 30 mpg plus cool or hot) Now I can wait until the warranty is over and live with the damage that wait causes or I can cool the thing down, give it chance to live longer and live with that result.

This isn't even a thing I give a seconds thought anymore. Tell you what I told the salesman and the service writer. You decide not to stand behind your product when it fails and I guarantee it's the last one I ever buy and I'll write all six kids and fourteen grand kids out of my will if they buy one. I will NOT be blackmailed into suicide. :wtf:

dieselfan1 · July 31, 2020

They would never know you did it, so it couldn't void anything.

For what it's worth, this is a great thing to do in my opinion. I went to the track last weekend with my truck, it was well over 85 degrees with +80% humidity, that nasty wet hot feeling. The drive there my temps got to 150ish on the open road, let my truck cool off while the track was getting ready. Once the lanes opened I got about 12 runs down the track in about 90 minutes, I hot lapped it back to back many times. It took 4-5 passes for me to even breach 190 degrees and all the runs after that the temps stayed under 196 just beating on it. I left the track and the temps still above 190, within 10 miles it was back down to 165. There is no way it would have ever done that with the thermostat still installed.

Do you go to BIR?

Sent from my Pixel 3 using Tapatalk

rav3 · July 31, 2020

On 7/30/2020 at 3:08 PM, Grumpy Bear said:

Fluid leaves the transmission via the thermostats top line and is routed to the drivers side radiator tank (hot side on your model) then from there to the AC condensers top half and back to the thermostat. Some trucks go only to the radiator. The six cylinders like mine go to the passenger side tank (cold) and back to the thermostat.

Water heats faster than the trans fluid so in the beginning the radiator side works like a fluid heater or should if it had any flow at all but the GM thermostat does not have a minimum flow bypass and has a 192 ish F trigger temperature. So as is fluid is short circuited back to the transmission until enough work has been put into the fluid to get the pill in the thermostat off its seat after which it regulates to roughly 192 ish F. As the V8 models use the hot tank they get the extra cooler in the AC condenser for heavier work and by and large they run a bit warmer than the V6. About 20 degrees or so.

Flipping the pill will heat the fluid faster in the winter and keep it cooler year around UNTIL you ask more from the system than it can deliver. Steep long hill in Death valley at max GVWR sort of thing.

There isn't a transmission builder worth his wage that wouldn't tell you 180 F is plenty hot and staying under 175 F day in and day out will drastically length life of the unit. B&M, PATC, SONNAX, TransGo.

My 6L80E runs and shift as pretty as a peach with the pill flipped and a cooler water thermostat (bonus information) 123K trouble free miles. Red Line D6 fluid. Runs 130 ish winter and 160 summer. 170 F water thermostat. summer 180 winter.

JohnA ran a full series on this modification specific to the V8's a few years back. Great work and write up. He knows way more than I on that combination.

Does anyone know the reasoning behind GM's choice to have the transmission thermostat set at the 192F ish temperature for the transmission? To me, that sound a little high since it's my understanding that heat kills the fluid. I'm just curious if there any GM engineers on this site that can explain it.

My old engineering mind would suggest to make the fluid as thin as possible to gain some MPG in this world of EPA driven efficiency over common sense. I've heard on here that the pre K2xx models didn't have this device. Sorta like adding the front closing shutters to make this brick more aerodynamic.

Grumpy Bear · July 31, 2020

I can take an educated guess. Warm fluid is less viscous and spinning parts in a less viscous fluid takes less gross power. That's the theory. Most lubricating oils however are 'slickest' around 160 F ish so it doesn't play out. Worse, in the winter it takes longer for the fluid to heat with a zero min flow bypass thermostat. Net/net a failed plan but one that earn points with the EPA, CARB etc. It's the cheapest way possible to fail at a plan goal. Unless the goal is to fail the transmission and build shop invoices. Then they hit that nail square on the head.

Bob2C · July 31, 2020

The one thing I have noticed is when mine is actually running at 195 it will cool down fairly quick to 180ish in about 30 min after I turn the vehicle off.

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