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Discussion Starter · #262 ·
Got some time to do the thermostat bypass today and it was one of those expect the worst and hope for the best things given that I’m in the northeast.

After getting the transmission lines off this is what I was left with. Here’s my thermostat housing.


The first thing I was worried about was the snap ring. I was hoping it wasn’t going to be rusted or too corroded to the point that it wouldn’t pop out. After some WD40 and using a pick to clean out the holes in the snap ring, I was able to slowly use my snap ring pliers and work it out.




The next “worry” I had that I had to tackle was if the cap was corroded to the point that it “welded” itself to the housing. With a pair of vise grips I was able to gently wiggle the cap loose, and eventually off.


Contents of the thermostat housing, even have some gunk on the cap.


The inside is incredibly clean, especially since I had the transmission flushed less than 5K miles ago.


Contents of the STL010 bypass kit


Put the O-Rings onto their corresponding parts


All parts fully assembled and back in the housing


Snap ring back on and fully seated


Fully cleaned up (as best as I could)


All re-installed in the truck!


Just make sure that the lines are clipped in properly and fully before starting the truck or it will pile all of its transmission fluid… Ask me how I know… lol
 

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Discussion Starter · #264 ·
what, if any, are the drawbacks of doing this? if there are none, why didnt GM do it from the factory?
GM finally realized the bad design and released an updated a transmission thermostat replacement, but it wasn't as good of an option for me since I have a 14/15 which has difference connectors and that means I would have had to replace my transmission lines as well. Both the GM option or this one will open the TSTAT around 150 degrees instead of 190 so the transmission can run cooler and prolong life.
 

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I did this on my father's 18 8l90 as well. Nice easy install.

His thermostat failed by the little pin that's in there punching through the plastic piece and not allowing it to open at all. Really a crap design that shouldn't be there to begin with.
 

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Discussion Starter · #266 ·
I did this on my father's 18 8l90 as well. Nice easy install.

His thermostat failed by the little pin that's in there punching through the plastic piece and not allowing it to open at all. Really a crap design that shouldn't be there to begin with.
Nope, shouldn’t be at all, but at least it’s an easier repair with plenty of options for those who actually care about their trucks


Sent from my iPhone using Tapatalk
 

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GM finally realized the bad design and released an updated a transmission thermostat replacement, but it wasn't as good of an option for me since I have a 14/15 which has difference connectors and that means I would have had to replace my transmission lines as well. Both the GM option or this one will open the TSTAT around 150 degrees instead of 190 so the transmission can run cooler and prolong life.
thanks for the info. do you have a link to the kit you got to do this?
 

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Discussion Starter · #268 ·

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6L80e's are plagued with problems in comparison to the GMT900 or GMT800 (4l60e jokes aside). For example my trucks had a flipped thermostat since like 55,000 miles, has 98,000 now. The hottest my 6L80E has ever got was towing last month in 95 degree weather and it got to 190 in stop and go traffic with a 5500lb trailer + a bed full of spare tires. And before someone tells me its "too cold" my 4l60e had a trucool 40k and that thing has 220,000 miles, plows, tows and in the winter runs maybe 100 degrees? My 6L80e runs like 110-130 in the winter.
 

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Discussion Starter · #270 ·
6L80e's are plagued with problems in comparison to the GMT900 or GMT800 (4l60e jokes aside). For example my trucks had a flipped thermostat since like 55,000 miles, has 98,000 now. The hottest my 6L80E has ever got was towing last month in 95 degree weather and it got to 190 in stop and go traffic with a 5500lb trailer + a bed full of spare tires. And before someone tells me its "too cold" my 4l60e had a trucool 40k and that thing has 220,000 miles, plows, tows and in the winter runs maybe 100 degrees? My 6L80e runs like 110-130 in the winter.
Hitting 190 after flipping the pill? Just imagine what that temp would have been if you didn't do anything to the thermostat? We would be seeing an update post about a new transmission or trading in the truck... I'm glad I did it (even though I am at 68K right now) and I barely do any towing or any heavy "work" with it.
 
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