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History of the Duramax Diesel Engine

Updated on Apr 28, 2025

Half-ton pickups were well established and by all rights ruled the scene during the 1990s, but the ¾- and 1-ton segments were quickly gaining popularity. Dodge had paired with over-the-road engine manufacturer Cummins to provide diesel engines for its heavy-duty needs, Ford selected Navistar International to build its PowerStroke engine, and General Motors was utilizing engines from Detroit Diesel.

In 1996 General Motors was finalizing plans for its next-generation of full-size trucks, code named the GMT800 platform. At the time, GM’s market share of the heavy-duty diesel segment was widely reported to be around three percent. These low sales figures were due principally to the outdated and underperforming Detroit Diesel 6.5L diesel V-8, which GM had been utilizing since 1992. Producing at its peak 215 horsepower and 440 lb-ft of torque, the 6.5L was built to be a workhorse—not a claims queen. It was becoming clear that the buying public was gravitating toward its higher power Cummins and PowerStroke competition.

Who Makes Duramax?

Executives at GM knew that for their new truck to be a success, it would need a best-in-class diesel engine. So the search began for a partner to build the company’s new oil burner. Requests for proposals were sent to all possible engine manufacturers at the time, and in the end the decision was made to go with a company not only familiar with heavy-duty engines but that was also already a partner of General Motors—Isuzu.

Isuzu’s plan called for a clean-sheet design, a brand-new engine from the ground up that would be ready for production by year 2003. This posed a problem for the engineering staff at GM, as the new GMT800 pickup would begin production in 2000, a full three years sooner. In early 1997, GM’s chairman at the time, Jack Smith, called a meeting with his counterpart at Isuzu, Kazuhira Seki, and the pair agreed to accelerate the engine development to meet GM’s strict timeline. A project management team was established in May 1997 that consisted of Jim Hogan from the GM Truck Group, Jim Kerekes from GM Powertrain, and Yoshihiro Tadaki from Isuzu.

The first running engine prototypes were completed in early 1998 in Japan and were installed in test mules in the United States shortly thereafter. Development continued at a furious pace both at GM Powertrain’s Romulus Engineering Lab in Michigan and at Isuzu’s facilities in Japan.

A new company was formed out of the engine program in September 1998. The joint venture, named DMAX Ltd., was originally owned 60 percent by Isuzu Diesel Services of America, Inc. and 40 percent by General Motors. In May 2022, DMAX became a wholly owned subsidiary of GM.

The name is a combination of diesel (D) and maximum (MAX), representing maximum diesel engine durability, reliability, cleanliness, efficiency, and power. The company is headquartered in Moraine, Ohio, where a new 584,000 square foot production facility was erected near the old 6.5L engine plant. Many of the former employees were able to transfer over to working at the new plant when it came online.

What Is a Duramax?

A new millennium spawned fear, anticipation, and the birth of the segment-changing Duramax engine that would revolutionize the diesel scene. The first production Duramax diesel engine rolled off the assembly line on July 17, 2000, and shortly thereafter the all-new, now-iconic Duramax Diesel 6600 engine made its public debut in the 2001 Chevrolet Silverado 2500/3500HD and GMC Sierra 2500/3500HD. As the fastest new engine development program at GM at the time, the Duramax went from idea to reality in just about 37 months.

The engine was an immediate success, launching GM’s market share of HD pickups from next-to-nothing to 30 percent practically overnight. The Duramax racked up a bevy of awards in its first years as well. It made Wards “10 Best Engines” list in 2001 and 2002, received Popular Science’s “Best of What’s New” award in 2000, and the Duramax-equipped Silverado was named Motor Trend’s 2001 Truck of the Year.

This new diesel engine was a 6.6L 90-degree V-8 that sported high-pressure common-rail direct injection, over-head-valve aluminum heads with four valves per cylinder, and a single turbocharger that resides at the rear of the lifter valley and feeds air through a large forward-mounted intercooler. Since its humble beginnings, the Duramax engine has gone through half a dozen generations. Power levels have climbed from 300 horsepower and 520 lb-ft of torque in 2001 to a monstrous 470 horsepower and 975 lb-ft of torque in 2024. The success of the 6.6L Duramax engine helped change the public’s outlook on diesel engines and has spawned a cult-like following.

DMAX Ltd. has produced over 3.1 million Duramax diesel engines since the powerplant’s launch at the turn of the century, with 1 million by April 2007, 1.5 million by November 2012, and 2 million by March 2017.

What Is an RPO Code?

General Motors uses three-digit alphanumeric Regular Production Option (RPO) code combinations to guide vehicles through production. Options such as paint color, engine, suspension, and even axle type all carry unique RPO codes.

Within the RPO codes, the first digit defines the family. For example, L belongs to engines, M to transmissions, Z to suspension, G to axles, and so on. Some RPO codes gain notoriety and go on to be used as descriptive terms, as is the case with Duramax engine codes. Other notable examples include the LS engine family (LS1, LS2, LSX, LSA, etc.), suspension options (Z71, ZR2, etc.), and performance packages (Z06, ZR1, etc.). They also provide a quick and easy way to identify which engine is being discussed, as is the case with generations of Duramax engines—which we will dig into next time.

When it comes to your Duramax-powered pickup truck, RealTruck has you covered! Check out our top parts and accessories for the 2024 Chevy Silverado 2500HD and 2024 GMC Sierra 2500HD. While you’re at it, drop by the RealSource blog today to see what’s new in the truck world.