Chevy's 6.6L Duramax Diesel: Everything You Need To Know About The Engine

General Motors has been using Duramax diesel engines in certain workhorse models for nearly a quarter century. The 6.6-liter V8 version which powers Chevy Silverado 2500/3500HD and GMC Sierra Heavy Duty pickups got some important updates in 2024 and remains a trustworthy centerpiece in GM's lineup. Since its debut in 2001, truck and SUV owners have praised the 6.6-liter Duramax engine for its robust low-end torque, surprising efficiency, and durability.

The history of the Duramax engine family goes back to 2001, when GM teamed up with Isuzu to challenge Ford's Powerstroke and the Cummins engine used in Dodge (now Ram) trucks. Duramax engines have some tough competition, but GM's workhorse diesel earned its place among the best truck powerplants around thanks to its sturdy construction and the gradual addition of some state-of-the-art touches. The design and production of Duramax engines happens under the umbrella of DMAX Ltd, a subsidiary of GM with a half-million square foot factory in Dayton, Ohio. In addition to the aforementioned Chevy and GMC pickups, you can find the 6.6-liter Duramax under the hood of select years of the Chevy Tahoe and Suburban as well as the GMC Yukon. 

The current version of the L5P 6.6L Duramax turbo-diesel V8 pumps out a solid 470 horsepower and produces 90% of its 975 pound-feet of max torque at just 1,550 rpm. The turbocharger is an impressive bit of engineering, with electronically controlled vanes inside that manage exhaust flow. In many GM models, the 6.6-liter Duramax is paired to a slick-shifting Allison 10-speed automatic transmission, allowing these rigs to work well in a variety of use cases and environments. When GM uses the label "heavy-duty" on a Duramax-powered truck, that's no joke. Trucks fitted with the 6.6-liter Duramax Diesel can tow up to 36,000 pounds and carry as much as 7,237 pounds of payload. That's due in part to the engine's 16.0:1 compression ratio and direct fuel injection system with a high-pressure common rail. 

The cylinder head and intake manifold of the current version are cast aluminum to save weight, but the block, exhaust manifold, and main bearing caps are cast iron for added strength. The forged steel crankshaft and camshaft are connected by Powder Metal (PM) iron rods, all of which help it withstand the rigors of constant and demanding use. It might surprise you, then, how efficiently the 6.6 Duramax consumes fuel. Of course, it's not going to match up well with a compact car or family sedan, but for an engine of its size and power it does reasonably well. Drivers report 6.6-liter Duramax fuel efficiency of between 13 and 17 mpg in city driving and as much as 23 mpg on the highway.

Diesel engines are great for many things, but they're generally not known as being environmentally friendly. However, GM is determined to change this and have set DMAX, Ltd. on a mission to clean up their diesel heavy hitter. The current 6.6-liter Duramax comes loaded with up-to-date emissions control features like Exhaust Gas Recirculation (EGR), Diesel Particulate Filters (DPF), and Selective Catalytic Reduction (SCR). These features help reduce harmful tailpipe emissions, keeping your truck powerful without smoking out the neighborhood. The 6.6-liter Duramax V8 runs on ultra-low sulfur diesel fuel as well as even more eco-friendly B20 Biodiesel. 

Aluminum pistons with built-in oil cooling passages compress air to ignite the fuel, and ceramic glow plugs and the advanced temperature management system allow for starts in temperatures as low as -40º F; which — coincidentally — is also -40ºC. GM also uses a gear-driven water pump and integrated oil cooler to keep the engine at the proper temperature when it's working hard. The tried-and-true pushrod overhead valve design with four valves per cylinder helps optimize performance and reliability, and an oil separator helps captures and recycles the mist from blow-by and puts it to use lubricating the engine. The head employs mechanical roller-style valve lifters for smooth power delivery and consistent operation over a long period of time. 

GM also employs technology like real-time engine monitoring and advanced fuel injection controls to help ensure the 6.6-liter Duramax delivers optimum performance. There's also a ninth injector that sprays a mix of fuel and diesel exhaust fluid (DEF) just behind the turbocharger to help burn off particulate emissions that make it that far down the exhaust.