GM Retires 6.6L Duramax V8 Diesel, 8.3L Mongoose Inline-Six to Power 2027 Trucks

General Motors is ending production of its 6.6-liter Duramax V8 turbo diesel and replacing it with an all-new 8.3-liter inline-six diesel engine, internally codenamed Mongoose, for the 2027 model year. This marks the end of an era for the V8 oil-burner that has powered heavy-duty Chevrolet Silverado and GMC Sierra trucks for years.

The new Mongoose engine displaces 8.3 liters and adopts an inline-six configuration, a layout known for smoothness and low-end torque. It is expected to deliver improved fuel efficiency and reduced emissions compared to the outgoing V8, while maintaining the towing and hauling capabilities that heavy-duty truck buyers demand.

The shift reflects broader industry trends toward more efficient diesel powerplants as emissions regulations tighten. GM’s move follows similar downsizing and re-engineering efforts by other manufacturers, though the Mongoose represents a significant increase in displacement over the 6.6L V8.

Details on power output, torque, and availability across Chevrolet and GMC heavy-duty lineup are expected closer to the 2027 launch. Fleet operators and diesel enthusiasts alike will be watching closely as the Mongoose enters production.