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Duramax is the name of a series of diesel engines built by General Motors from 2001 onwards. Several GM vehicles have been offered with a Duramax diesel engine over the years, the most notable example being the Chevrolet Silverado and its GMC counterpart, the Sierra. Duramax-powered vehicles have gained a reputation as reliable diesel workhorses, suitable for heavy towing and hauling. Reliability is another of the Duramax’s strong points; a Duramax engine can be expected to last around 200-300,000 miles without major issues.

Key Duramax Diesel Engines

LB7

In 2001, the 6.6-liter, 300-horsepower LB7 was the first Duramax engine used in a GM vehicle (Chevrolet Kodiak, GMC TopKick, Chevrolet Silverado, and GMC Sierra). It is widely considered to be an extremely reliable engine, partly due to its simplicity: the lack of emissions devices means it has a lower potential for failure due to its smaller number of parts. However, there are a few potential drawbacks to keep an eye out for, the main ones being head gasket issues and injector failure, with most LB7 engines requiring new injectors at some point over the course of their life cycle. The LB7 was in production until the start of 2004, when it was replaced by the LLY.

LLY

The second Duramax engine, the LLY, first arrived on the market in mid-2004, with an increase in both power output (310 hp against the LB7’s 300) and torque (590 lb-ft against the LB7’s 520). This was partly due to the fact that the LLY came with the largest turbocharger ever offered in a Duramax engine. A number of upgrades also mitigated some of the issues that had affected the LB7, including upgraded injectors and redesigned valve covers that allowed for easier access. An EGR system (exhaust gas recirculation) was also added to reduce emissions. There are still a couple of problems to watch out for in this generation Duramax, such as blown head gaskets and overheating issues. The LLY engine was used in the following vehicles:

• 2006 Hummer H1 Alpha
• Chevrolet Silverado/GMC Sierra 2500HD/3500
• Chevrolet Kodiak
• GMC Savana van

LBZ

The LBZ engine hit the market in 2005, with increases in power output and torque. Several components, including the engine block, cylinder heads, fuel pump, and fuel injectors, were upgraded, substantially increasing the engine’s reliability and making it easier to modify. LBZ engines are also sought after today due to being pre-DPF (diesel particulate filter), their only emission control device being the EGR system. The LBZ engine stayed in production for two years before being replaced by the LMM in 2007. The LBZ was available on the following vehicles:

• Chevrolet Kodiak
• GMC TopKick
• Chevrolet Silverado
• GMC Sierra

LMM

Producing 365 hp and 660 lb/ft of torque in certain Silverados, the LMM engine debuted in mid-2007 and remained the only Duramax engine on the market until 2010. Several emission controls were added, such as an oxidation catalyst, a DPF (diesel particulate filter), and a new EGR system, which resulted in slightly lower fuel economy. A modified version of the LMM was used in the short-lived Trident Iceni, the “world’s fastest diesel sports car.”

LML

The LML engine arrived in 2011 with a power output of 397 hp and up to 765 lb-ft of torque in stock form. Only available in the Chevrolet Silverado and GMC Sierra, the LML was the most emissions-efficient Duramax engine to date thanks to its upgraded fuel injectors and oil pump; the addition of diesel exhaust fluid (urea injection) brought further improvements to the LML’s emissions. Some of the upgrades introduced for emission control reasons also provided a boost in performance, making the LML a popular choice of Duramax engine.

LGH

Used in the 2010 and 2011 model years for the Chevrolet Express/GMC Savana and the Chevrolet Silverado/GMC Sierra HD, the LGH engine produces 335 hp and 685 lb-ft of torque. The LGH shares most of its key design features with the LML engine, essentially being a detuned version of the LML, used primarily in chassis-cab and box-delete trucks. The main difference lies in the EGR system, which has a single cooler (the EGR system in the LML engine comes with dual coolers).

L5P

The L5P engine was first introduced in 2017; it produced 445 hp and 910 lb-ft of torque, making it the most powerful diesel engine GM had ever built. This boost in performance came about thanks to several performance upgrades, including the addition of cast-aluminum cylinder heads (which allow for additional airflow) and a lift pump (which improves the reliability of the fuel system). A new version of the L5P engine was introduced for the 2024 model year, with a further improvement in power output: the new version produces 470 hp and 975 lb-ft of torque.

L5D

The L5D is a detuned version of the L5P, primarily used in commercial vehicle applications (you can find an L5D in the Chevrolet Silverado 4500HD, 5500HD, 6500HD, and some International CV trucks). The L5D engine is paired with a choice of three Allison six-speed automatic transmissions. The L5D produces a power output of 350 hp and 700 lb-ft of torque.

What Are The Best Duramax Engines?

All Duramax engines have their own strong points and potential issues to watch out for, but what is the best Duramax engine? Here are three of the most popular Duramax engines and their individual strengths:

• LBZ: the LBZ engine made several improvements in terms of reliability, mitigating the injector and head gasket issues that had plagued previous engines in the Duramax family. The LBZ engine also does not have a DPF (diesel particulate filter), meaning less maintenance is needed (the DPF requires periodic “regeneration cycles” to remove accumulated particles, which keeps the system functioning efficiently)
• L5P: the newest member of the Duramax family, the L5P is also the most powerful to date, with the highest power output and torque of any Duramax engine, so if you regularly use your vehicle for heavy towing, this may be the right choice for you. Reliability-wise, the L5P hasn’t had a chance to prove itself yet as it is still fairly new, but so far no major issues have arisen.
• LB7: Being the oldest engine in the Duramax lineup, the LB7 is less mechanically complex. This does mean emissions will be higher, as the LB7 does not come with the emission-limiting technology present in later models. However, it also means less maintenance, less potential for failure, and more potential for customization. If you are keen on modifying your vehicle, the LB7 offers a good base for you to add upgrades of your choice.