The Mishimoto thermal bypass valve kit replaces the failure-prone factory bypass valve on the 2017-2019 Chevrolet/GMC 6.6L Duramax L5P with the Allison 1000 transmission. The stock valve withholds transmission fluid from the cooler until operating temperature, but its thermostat can fail closed — starving the cooler and overheating the transmission. This CNC-machined billet aluminum valve includes a fully serviceable thermostat for fast cold-climate warm-up, plus an installable thermostat-bypass insert for constant cooling in hot climates or heavy towing, with machined internal passages and integrated heat-sink cooling fins. Black anodized, OEM/Mishimoto activation temp 185°F.
| Type | Transmission thermal bypass valve kit (thermostatic) |
| Transmission | Allison 1000 |
| Material | CNC-machined billet aluminum, black anodized |
| Thermostat | Serviceable, 185°F; installable full-bypass insert |
| Part Number | MMTC-L5P-TBV |
| Warranty | Mishimoto Lifetime Warranty |
This part fits:
| Year | Make | Model | Submodel |
|---|---|---|---|
| 2017-2019 | Chevrolet | Silverado 2500 HD / 3500 HD | 6.6L Duramax L5P (all trims) |
| 2017-2019 | GMC | Sierra 2500 HD / 3500 HD | 6.6L Duramax L5P (all trims) |
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Returns: 30-day returns on new, unused items in original packaging. See the full Refund Policy.
