The Mishimoto full-flow thermal bypass valve kit replaces the failure-prone factory bypass valve on the Chevrolet/GMC 6.6L Duramax L5P with the Allison 1000 transmission. The stock valve withholds transmission fluid from the cooler until operating temperature, and its thermostat can fail closed — starving the cooler and overheating the transmission. This CNC-machined billet aluminum full-flow valve eliminates the thermostat entirely, pumping fluid through the cooler the moment the truck starts for constant cooling — ideal for hot climates, heavy towing, or extreme driving. Black anodized, backed by the Mishimoto Lifetime Warranty.
| Brand | Mishimoto |
| Type | Full-flow transmission thermal bypass valve kit |
| Transmission | Allison 1000 |
| Material | CNC-machined billet aluminum, black anodized |
| Function | Full-flow (no thermostat); constant cooler flow |
| Warranty | Mishimoto Lifetime Warranty |
This part fits:
| Year | Make | Model | Submodel |
|---|---|---|---|
| 2017-2021 | Chevrolet | Silverado 2500 HD / 3500 HD | 6.6L Duramax L5P (all trims) |
| 2017-2021 | GMC | Sierra 2500 HD / 3500 HD | 6.6L Duramax L5P (all trims) |
