Superior STL010 Sure Cool Cooler Bypass Upgrade Kit for GM 6L80 / 6L90 / 8L90

The GM 6-speeds, the 6L80, 6L90, and later 8L90, all ship with a thermal bypass valve in the cooler circuit that is supposed to hold fluid back until the transmission warms up. In practice that valve is one of the reasons these units cook themselves. It delays getting fluid out to the cooler, it can stick, and it makes checking the level a guessing game because you cannot get an accurate reading until the fluid is fully up to temperature. On a truck that tows or spends time under load, that adds up to an overheated transmission and a short clutch life. This kit is the known fix.

The Sure Cool upgrade replaces the factory thermal bypass behavior with a design that fills the external cooler immediately, so fresh fluid is moving through the cooler from the moment you start driving instead of after a long warm-up. Cutting that delay is what brings the average operating temperature down, and shops running it report drops of as much as 20 percent. Cooler fluid means the ATF lives longer, the clutches see less heat, and you buy back a real margin before the transmission is ever in danger of overheating on a grade or with a trailer behind it.

It also solves the level-check headache. With the cooler filling right away you can verify the fluid level without running the truck through a full warm-up cycle first, which makes a service or a fluid change a lot less of a fight. The kit installs in the cooler line circuit and fits the GM 6L80, 6L90, and 8L90 families. If you own or build one of these transmissions, this is one of the cheapest pieces of insurance you can put on it. Ships from the USA.