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Mishimoto thermal bypass valve kit for 2017–2019 Chevrolet/GMC 6.6L Duramax L5P replaces the failure-prone stock in-line thermostat with a CNC-machined aluminum upgrade that improves flow to the transmission cooler while retaining a serviceable thermostat for quicker warm-up. Machined internal passages and cooling fins enhance cooling; the kit fits L5P Allison transmissions and comes with a durable black anodized finish and lifetime warranty.
Mishimoto 2017+ GMC 6.6L Duramax L5P Transmission Thermal Bypass Valve Kit
