Duramax Diesel FAQ

Answers to Frequently Asked Questions about the Duramax Diesel

The namesake Duramax diesel was first introduced into production for the 2001 model year in Chevrolet and GMC fullsize pickup applications. At the time of its release, the engine produced an impressive 300 horsepower and 520 lb-ft of torque. Fast forward to 2020 and the latest generation of the 6.6L Duramax peaks at an earth shaking 445 horsepower and 910 lb-ft of torque. Here are some of the most commonly asked questions we receive about the Duramax 6600 engine platform.

Who developed the Duramax diesel?

The Duramax diesel was developed by and continues to be manufactured by DMax Ltd. The original Duramax diesel engine design is said to have been engineered and developed by Isuzu Motors, while GM was responsible for the electronic engine calibration and the integration of the new engine platform into their vehicles.

Who is DMAX?

DMAX is the manufacturer responsible for the development, manufacturing, and assembly of the 6.6L Duramax diesel. The company was originally formed as a joint venture between General Motors and Isuzu Motors Ltd, with GM holding a 60 percent stake in the company and Isuzu holding the remaining 40 percent. In 2017, DMAX celebrated the 2 millionth 6.6L Duramax diesel built at their facility in Moraine, Ohio.

Why did GM partner with Isuzu?

Isuzu has extensive knowledge in the diesel engine segment, particularly in the medium and heavy duty markets. Their portfolio includes diesel engines of various sizes for commercial and industrial applications. Furthermore, Isuzu has maintained an overwhelmingly positive reputation with regard to engine longevity and reliability. Considering the popularity and success of the Duramax 6600 engine family, their expertise has been priceless to General Motors.

Recall that the 6.5L diesel, although commercially successful due to the wide scope of its applications, was not particular triumphant in its reputation and unfortunately didn't compete well in the pickup truck segment as it approached the end of its cycle. GM was the obvious beneficiary from the DMAX joint venture, as the Duramax diesel engine platform and brand name have flourished since its inception.

Where is the 6.6L Duramax built?

Since the introduction of the Duramax 6600 engine family, all 6.6L Duramax diesels have been assembled at the DMAX assembly plant in Moraine, Ohio.

Which Duramax diesel do I have?

Most Duramax diesels can be identified by their model year, however there are several transitional years in which two engine generations may have briefly co-existed. The chart below can help you identify, with absolute certainty, which engine your vehicle is equipped with:

Vehicle Model Year(s)

Engine RPO Code

8th Digit of VIN

2001 - 2004 pickup/chassis cab



2004 - 2006 pickup/chassis cab



2006 - 2007 pickup/chassis cab



2007 - 2010 pickup/chassis cab



2011 - 2012 chassis cab



2011 - 2012 pickup truck



2013 - 2016 pickup/chassis cab

2011 - 2016 van



2017 - current chassis cab



2017 - current pickup truck



For factory power ratings, see: 6.6L Duramax horsepower and torque timeline. For additional details on VIN number decoding, see: What Duramax diesel do I have?

What is the best Duramax diesel?

The 2006 to 2007 model year LBZ is a fan favorite; it retains a simplified layout sans exhaust aftertreatment system and healthy horsepower and torque numbers from the factory. The LB7 is also well known for delivering reasonably high fuel economy, and its variable geometry turbocharger offers reduced turbo lag over previous fixed geometry models. That being said, each Duramax generation has its advantages and, in most cases, common problems that are specific to that variant.

Are all 6.6L Duramax engines the same?

The bore and stroke dimensions have remained the same over the years, thus the displacement remains at 6.6 liters. However, the engine has evolved significantly through the years, with each generation gaining improvements over the previous. If you compared the original LB7 to the 2017+ L5P, you wouldn't notice many similarities, whereas an LBZ and an LMM appear noticeably similar.

What is the 7.8L Duramax?

The 7.8L Duramax is an Isuzu 6H series inline 6 turbodiesel re-branded for GMC TopKick and Chevrolet Kodiak applications. It was introduced for the 2003 model year and retired after 2009, at which point GM took a hiatus from the medium duty truck segment. The engine is not related in any form to the 6.6L Duramax V-8, but does hint at the degree of collaboration between GM and Isuzu.

Is the 3.0L Duramax a smaller version of the 6.6L Duramax?

There are zero similarities between the 2020+ 3.0L Duramax diesel and any generation of the 6.6L Duramax. The 3.0L Duramax is a small displacement, inline 6 cylinder turbodiesel manufactured by GM and only available in the Chevrolet Silverado 1500 and GMC Sierra 1500. It's a highly fuel efficient engine platform that offers respectable horsepower and torque, but would be significantly underpowered in 2500/3500 HD applications that the 6.6L Duramax is found in.

Why has the Duramax diesel platform changed so many times?

The evolution of the Duramax diesel is representative of the tight competition in the diesel pickup and chassis cab segments and the phasing in of stringent emissions regulations in the United States. Each time a new Duramax generation is released, it is done so with improved horsepower and torque ratings and, in many instances, additional emission control features such as exhaust aftertreatment systems. With more power comes greater internal stresses that the engine most overcome, and thus structural improvements have been necessary to allow these engines to survive at greater performance levels without compromising reliability and longevity; customers choose diesel engines for a number of reasons, but reliability and longevity are arguably at the top of the list. With each iteration of the Duramax 6600 engine platform, we see enhanced features, strengthened components, improved performance, and even more coherent integration between powertrain components.

Does my Duramax diesel have an engine block heater?

All Duramax engines are factory equipped with an engine block heater. The block heater plug comes taped and/or zip tied to the wire loom traveling from the passenger battery to the frame rail. Follow the negative battery cable and you'll bump right into it.

Does the Duramax diesel use an electric lift pump?

The L5P is the only generation of the 6.6L Duramax diesel to employ an electric lift pump on pickup truck models; some previous generation chassis cabs may or may not have an electric lift pump. For the 2001 to 2016 model years, fuel is drawn from the tank via a positive displacement fuel pump integrated into the CP3 or CP4 high pressure injection pump. In lieu of an electric lift pump, these models incorporate a manual plunger into the fuel filter housing to prime and bleed the fuel system after service.

What injection pump does my Duramax diesel have?

2001 to 2010 model year engines utilize the tried-and-true Bosch CP3.3 high pressure injection pump. 2011 to 2016 model year engines employ the Bosch CP4.2 high pressure injection pump. For 2017 to current model years, the L5P relies on a Denso high pressure injection pump. Also noteworthy, 2001 to 2016 model year engines have piezoelectric fuel injectors, while the 2017 and later L5P engines utilize Denso solenoid type fuel injectors.