TransGo 6L80/6L90/8L90 Cooler Flow Bypass Delete Kit

This is TransGo's drop-in cooler flow bypass delete for the GM 6L80, 6L90 and 8L90 (part number 6L80-CLR-BYPASS). From the factory these transmissions use a thermostatic element in the cooler circuit that holds fluid back from the external cooler until the trans is warm. That element sticks, restricts flow, and lets fluid temperature climb, and heat is the number one killer of the clutches and the torque converter in these units. This kit eliminates the thermostatic assembly so the cooler sees full flow the moment the truck is running.

It fits 2014-and-up 6L80 and 6L90, 2015-and-up 8L90, and 2017-2019 Allison transmissions behind Chevrolet, GMC and Cadillac trucks and SUVs. Owners running these behind a tow rig or a tuned truck report a 20 to 30 degree F drop in transmission temperature after the swap. A cooler transmission holds its fluid and friction material longer, which is the whole point of doing it before the pan shows metal.

Installation is a pan-off job that takes most people under half an hour: pull the pan, remove the factory thermostatic assembly from the cooler circuit, drop in the supplied bypass plug with its O-ring and spacer, seat the pin, and replace the end-cover O-ring before you refill. Because there is no warm-up cycle gating the cooler anymore, you can check and set fluid level right after the install instead of waiting. Kit ships from the USA, handling in 1-2 business days.