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

If you're doing heavy towing or live in a warm climate with your 2017-2019 Chevrolet or GMC 6.6L Duramax L5P, keeping your transmission fluid cool is critical. The Allison transmission in these trucks handles a lot of power, and excessive heat can quickly lead to damage. The stock thermal bypass valve is supposed to regulate fluid flow to the transmission cooler, only sending fluid when it reaches operating temperature. However, the thermostat inside this valve is known to fail, which can prevent fluid from ever reaching the cooler, leading to overheating.

Mishimoto has developed a full-flow thermal bypass valve upgrade to address this common issue. This kit replaces the stock valve with a CNC-machined billet aluminum unit that eliminates the internal thermostat. This means fluid will always flow to your transmission cooler, ensuring more effective cooling under all conditions. The internal passages are machined for improved flow, and cooling fins are integrated into the valve body itself to help dissipate heat. This upgrade is a solid option for anyone looking to maximize their transmission's cooling efficiency.

This kit installs in under an hour and comes with a durable black anodized finish. It's built to last and backed by Mishimoto's Lifetime Warranty.