Mishimoto 2017+ GMC 6.6L Duramax L5P Transmission Thermal Bypass Valve Kit

The Allison transmission in your 2017-2019 Chevrolet or GMC with the 6.6L Duramax L5P engine handles a lot of power, and that power creates heat. Keeping that heat in check is crucial for transmission longevity. The stock thermal bypass valve controls when transmission fluid flows to the cooler, but its internal thermostat can fail, preventing flow and leading to overheating. Mishimoto's thermal bypass valve upgrade is designed to replace that failure-prone stock part.

This kit features a CNC-machined billet aluminum valve body with strategically placed internal passages that improve fluid flow over the factory unit. It also includes cooling fins machined directly into the valve for extra heat dissipation. You can install it with a fully serviceable thermostat for faster warm-up in colder climates, or use the included bypass for constant cooling in warmer areas or during heavy towing. The black anodized finish not only looks sharp but also adds durability.

This upgrade is a solid option for anyone looking to ensure their Allison transmission stays cool under load. It installs in under an hour and is backed by Mishimoto's Lifetime Warranty.