- Joined
- Aug 3, 2024
- Messages
- 155
So I have a 2020 Silverado 1500 with the 5.3L and 8 speed auto. As is tradition the transmission has already had two warranty repairs, a new torque converter at .under 20K and a first gear solenoid not long afterwards. It's now out of warranty so it's time to get proactive about preventing future issues.
It's no secret these things run hot, fluid temps topping 200F is apparently the norm. GM might be OK with, that but I am not. We all know that heat is the biggest killer of automatic transmissions and I certainly can't see a down side to getting that fluid to run a bit (or a lot) cooler. GM actually released Service Bulletin 21-NA-199, which replaces the thermal bypass valve that wasn't fully open until 194F with an upgraded part that opens at 158F. For some reason that TSB only applies to the 6 speed, leaving the 8L90s to keep running hot.
Of course this issue has been known for quite some time and hasn't gone unaddressed. The internet (including BITOG) is rife with information on bringing down the temperature, from "flipping the pill" to aftermarket bypass kits. I decided to go a different route. I like the idea of keeping everything as OEM as possible and I wanted to use that new TBV for the 6L80, so I ordered one. I thought it would be a direct bolt-on but the housings are different and the metal lines wouldn't fit. The internals were identical other than the "pill" opening at a lower temp, so I just swapped the guts out.
Reinstalled, leak checked good so off for a test drive. I live in the tropics and summer was just starting so it didn't take long for the fluid to warm up. So far so good and I decided to just keep an eye on the fluid temp while doing normal day-to-day driving. I did just that and even in stop and go traffic with a heat index of over 100F, the fluid never got hotter than 160F. That's considerably lower than what I was getting before the swap, but I knew the ultimate test would be when we took our 20ft travel trailer out to the beach for a long weekend. That day came and it was a scorcher, and wouldn't you know it we got stuck in road construction, the ultimate torture test while pulling a trailer. None of that mattered though, stop and go or 60 mph down the highway with the A/C blasting, the fluid temps never went above 170F. I call that a win.
I know I over-complicated the whole thing and could have simply used a bypass kit, flipped the valve or just rolled the dice and let it be, but I kinda like my more "elegant" solution sticking with OEM parts, even if I had to bend the rules a little bit. I always say never argue with success, and so far I'm pretty happy with the outcome.
It's no secret these things run hot, fluid temps topping 200F is apparently the norm. GM might be OK with, that but I am not. We all know that heat is the biggest killer of automatic transmissions and I certainly can't see a down side to getting that fluid to run a bit (or a lot) cooler. GM actually released Service Bulletin 21-NA-199, which replaces the thermal bypass valve that wasn't fully open until 194F with an upgraded part that opens at 158F. For some reason that TSB only applies to the 6 speed, leaving the 8L90s to keep running hot.
Of course this issue has been known for quite some time and hasn't gone unaddressed. The internet (including BITOG) is rife with information on bringing down the temperature, from "flipping the pill" to aftermarket bypass kits. I decided to go a different route. I like the idea of keeping everything as OEM as possible and I wanted to use that new TBV for the 6L80, so I ordered one. I thought it would be a direct bolt-on but the housings are different and the metal lines wouldn't fit. The internals were identical other than the "pill" opening at a lower temp, so I just swapped the guts out.
Reinstalled, leak checked good so off for a test drive. I live in the tropics and summer was just starting so it didn't take long for the fluid to warm up. So far so good and I decided to just keep an eye on the fluid temp while doing normal day-to-day driving. I did just that and even in stop and go traffic with a heat index of over 100F, the fluid never got hotter than 160F. That's considerably lower than what I was getting before the swap, but I knew the ultimate test would be when we took our 20ft travel trailer out to the beach for a long weekend. That day came and it was a scorcher, and wouldn't you know it we got stuck in road construction, the ultimate torture test while pulling a trailer. None of that mattered though, stop and go or 60 mph down the highway with the A/C blasting, the fluid temps never went above 170F. I call that a win.
I know I over-complicated the whole thing and could have simply used a bypass kit, flipped the valve or just rolled the dice and let it be, but I kinda like my more "elegant" solution sticking with OEM parts, even if I had to bend the rules a little bit. I always say never argue with success, and so far I'm pretty happy with the outcome.
