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.
| 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 |
| Part Number | MMTC-L5P-TBVFF |
| 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) |
Shipping: In-stock orders placed before 3 PM EST ship the same day, and everything else ships within 24 hours. Standard, expedited, and overnight options are available at checkout. Backordered items ship as soon as we get them back in stock. Contact us for lead times. See the full Shipping Policy.
Returns: 30-day returns on new, unused items in original packaging. See the full Refund Policy.
