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GM 6.6L Duramax Engine Profile

By November 23rd, 2021No Comments

General Motors and Isuzu formed a joint venture, called DMAX, to produce a family of 6.6L Duramax diesel V8 engines for Chevrolet and GMC trucks, beginning in the 2001 model year. Over the past two decades, the joint venture has produced six variants of the Duramax diesel engine, including the 6.6L L5P Duramax diesel engine still in production today.

This 6.6L Duramax diesel engine guide is a part of our Diesel Engine Guide series to help with buying a school bus for sale.

This article will dive further into the 6.6L Duramax engine including:

  • Engine Overview
  • Engine Specs
  • Towing Capacity
  • Life Expectancy
  • Maintenance Requirements
  • Typically paired transmissions
  • Common engine problems
  • Engine comparisons to the 6.0L Powerstroke and 6.7L Powerstroke

6.6 Duramax Engine Overview

Chevy 6.6L Duramax engine short bus

The 6.6L Duramax engine variants evolved with different components needed to meet global mandates for reducing emissions while maintaining and even increasing horsepower and torque over time. Since the first model year, the engines have become popular options for General Motors pick-up trucks, vans and medium-duty trucks.

As the original Duramax model, the 6.6L LB7 Duramax diesel engine came to market in 2001 for Chevrolet Kodiak, Chevrolet Silverado, GMC Topkick, and GMC Sierra HD trucks. It has become a popular choice in the aftermarket due to the lack of emissions controls parts often blamed for engine issues in later models. The 32-valve design did include an experimental composite design cylinder head and a Bosch high-pressure common-rail direct injection system that reportedly had issues. Production of this variant ended in 2004.

The second diesel engine model, called 6.6L LLY Duramax, debuted in 2004. It was nearly identical to its LB7 predecessor in its componentry and lacked modern-day emissions control parts. GM fixed injector problems found in the previous engine model, but this variant reportedly had issues with overheating when towing heavy loads or driving in hot temperatures. The engine survived only one model year for Hummer H1 Alpha, Chevrolet Silverado, and GMC Sierra HD trucks. Production ended in 2005.

The third diesel engine model, called 6.6L LBZ Duramax, came to market in 2006 for General Motors Express and Savanna vans. It also was equipped for other trucks, including Chevrolet Silverado HD, Chevrolet Kodiak, GMC Sierra HD, and GMC Topkick. Mechanics view it as the best model in the Duramax diesel engine line because it lacked troublesome emissions control parts and included a new six-speed Allison transmission. General Motors had worked out the bugs found in previous engines (i.e., improved materials for bearings and cylinder blocks) and in the process managed to increase horsepower and torque. Changes from previous models included a revised piston design, thicker connecting rod section, all-new fuel injectors, revised variable-geometry turbocharger, and an all-new E35 controller to boost fuel flow. However, it was known to have issues with a factory lift pump. Production ended in 2007 as stricter emissions regulation became effective.

The fourth diesel engine model, called 6.6L LMM Duramax, debuted in 2007 and was nearly the same as its LBZ Duramax predecessor. The difference was new emissions control parts to meet increased air quality regulation in the U.S. at the time. The 6.6L LMM Duramax was equipped with an even more efficient variable-geometry turbocharging system, enhanced exhaust gas recirculation (EGR), and closed crankcase ventilation to reduce nitrogen oxides (NOx). Additional exhaust control came from a new diesel particulate filter (DPF) to reduce soot and particulate matter. The diesel engine powered the Chevrolet Express, GMC Savanna, Chevrolet Silverado HD, GMC Sierra HD, Chevrolet Kodiak, and GMC Topkick. The engine was known for cracking problems with its pistons. Production ended in 2011.

The fifth diesel model, called the 6.6L LML Duramax, was introduced in 2011 with enhanced emissions controls for Chevrolet Silverado HD and GMC Sierra HD trucks to meet even stricter air quality regulations. The diesel engine also managed to reduce noise vibrations and increase horsepower/torque by increasing the fuel system pressure. However, those component changes contributed to an injection pump issue. Production ended in 2016.

The sixth model called the 6.6L L5P Duramax, launched in 2017 and still is in production today for Chevrolet Silverado HD and GMC Sierra HD trucks. It is considered the best post-emissions Duramax engine, as previous issues with the injection pump and emissions systems have largely been fixed. The 6.6L L5P Duramax offers a quieter ride with more horsepower, torque (445 horsepower and 910 pound-feet torque) and power ratings than previous engine versions. In 2020, an Allison 10-speed automatic transmission replaced the old Allison 6-speed automatic transmission.

6.6L Duramax Engine Models

Engine variationsProduction YearsHorsepowerTorque
6.6L LB7 Duramax diesel engine2001 to 2004

Chevrolet Kodiak
GMC Topkick
Chevrolet Silverado HD
GMC Sierra HD
300 hp @ 3100 RPM520 lb-ft @ 1800 RPM
6.6L LLY Duramax diesel engine2004 to 2005

Hummer H1 Alpha Chevrolet Silverado HD
GMC Sierra HD
310 hp @ 3000 RPM590 lb-ft @ 1600 RPM
6.6L LBZ Duramax diesel engine2006 to 2007

Chevrolet Express
GMC Savana
Chevrolet Silverado HD
Chevrolet Kodiak
GMC Sierra HD
GMC Topkick
310 hp @ 3000 RPMLow: 590 lb-ft @ 1600 RPM
High: 605 lb-ft @ 1600 RPM
6.6L LMM Duramax diesel engine2007 to 2011

Chevrolet Express
GMC Savana
Chevrolet Silverado HD
Chevrolet Kodiak
GMC Sierra HD
GMC Topkick
330 hp @ 3000 RPM620 lb-ft @ 1600 RPM
6.6L LML Duramax diesel engine2011 to 2016

Chevrolet Silverado HD
GMC Sierra HD
397 hp @ 3000 RPM765 lb-ft @ 1600 RPM
6.6L L5P Duramax diesel engine2017 to present

Chevrolet Silverado HD
GMC Sierra HD
445 hp @ 2800 RPM910 lb-ft @ 1600 RPM

6.6 Duramax Transmissions

The Allison 1000 transmission has been the standard automatic transmission for 6.6L Duramax diesel engines since the first (LB7) model was introduced in 2001. Early engines featured 5-speed automatic transmissions, and 6-speed automatic transmission was introduced in later models (2006 LBZ model and on). In 2020, the old 6-speed automatic transmission was replaced by an Allison 10-speed automatic transmission, which puts more torque down in lower gears.

Towing with a 6.6 Duramax

The best tow capacity comes with the 6.6L L5P Duramax diesel engine. Chevrolet and GMC HD trucks (2017-2019 model years) with the L5P Duramax have a maximum tow capacity of 23,300 pounds. In 2021, tow capacity increased to 36,000 pounds. 

6.6 Duramax Engine Life Expectancy

The 6.6L Duramax diesel engine is sold with a warranty of 100,000 miles. Mechanics report that if properly maintained, the engine could survive up to 200,000 miles.

6.6 Duramax Engine Maintenance Requirements

Maintenance is critical to avoid common failures.

Engine variationsNormal conditions
6.6L Duramax Diesel EngineOil capacity: 10 quarts

Engine oil & air filter: 10,000 miles/6 months

Fuel filter: 15,000 miles (2001-2010 models); 22,500 miles (2011-2021 models)

Engine coolant: 150,000 miles/10 years

Transmission fluid & filter: 45,000 miles

6.6L Duramax Common Engine Problems

Mechanics report that the best 6.6L Duramax diesel engine was the initial LBZ model, although other models are relatively reliable and durable. Mechanics report the most problematic models were the 6.6L LLY and LML diesel engines. 

  • Fuel system trouble – In general, the 6.6L Duramax diesel engine uses an injection pump instead of a lift pump, and this can crack the fuel filter housing. The engine is known for two fuel-related issues. First, air can get into the fuel lines. Second, this reduces the amount of fuel running through the engine.
  • Water pump trouble – On average, the water pump should last more than 100,000 miles, but mechanics report they usually need to replace it at 80,000 miles. The LB7 model water pump has been known to leak. Water can seep from the underside of the pump and you need a good puller to get it off.
  • Overheating issues – If the water pump fails, the 6.6L Duramax diesel engine will overheat. A common issue with models in the 2005 or earlier models is a fan clutch failure, which can make the engine overheat, especially in hot weather.
  • Injector problems – The 6.6L Duramax is known for injector failures. In the 2001 to 2004 LB7 models, two primary issues are internal cracking and corrosion. Later engine models utilized a harder material and improved durability of the injectors.
  • Cracked pistons – This issue is most prominent in the 6.6L Duramax LBZ and LMM models. The failure is mostly due to low-quality castings. The cast-aluminum piston cracks along the center of the wrist pin. Most scenarios play out at power levels well over 600 horsepower.
  • Snapped crankshaft – The failure is most common in higher horsepower engines across all generations and not specific to any model year. The crankshaft usually breaks near the number one rod journal due to a combination of excessive rpm and large external counterweight.
  • Bent rods – The 6.6L Duramax LB7 and LLY models with high horsepower can create stress on the pistons, rods and the crank. The rods are the weakest link, even though they are made with forged steel. Mechanics report that they can bend long before breaking.

GM 6.6L Duramax vs. Ford 6.7L Powerstroke

General Motors’ 6.6L Duramax diesel engine series was in production a decade Ford introduced its own 6.7L Power Stroke diesel engine for Super Duty trucks in 2011. Over that time, GM was able to work out issues stemming from emissions equipment in mid-series production years. A choice over a diesel engine may come down to brand loyalty. 

Ford had a long-standing lead in the U.S. truck sales race with GM and other vehicle brands. The Ford 6.7L is the fourth generation of the Power Stroke diesel engine family, but it is the first of those engines to be built in-house by Ford. Ford was able to reduce losses from warranties/recalls of the Navistar International engines (from 6.4L and 6.0L Power Stroke engines) and gain a competitive edge in the growing diesel segment by designing, engineering and manufacturing its own diesel engine. 

Starting with a clean sheet, Ford designed the 6.7L Power Stroke diesel engine with 8-cylinders, an overhead valve (OHV), aluminum cylinder heads, cast-aluminum pistons and a compacted graphite iron block. During a decade of production, Ford continued to upgrade and refine the 6.7L diesel Power Stroke engine over three generations. The third generation of the Ford 6.7L Power Stroke diesel engine was introduced in 2020 and still is in production for 2022 model year Ford Super Duty trucks. In addition to more horsepower and over 1,000 lb-ft in torque, noteworthy improvements include a new steel piston design, revised variable geometry turbocharger, updated cylinder head design, and new fuel injection system.

Feature comparisonGM 6.6L Duramax diesel engineFord 6.7L Power Stroke diesel engine
Production years2001 to 2004 6.6L LB7 Duramax
2004 to 2005 6.6L LLY Duramax
2006 to 2007 6.6L LBZ Duramax
2007 to 2011 6.6L LMM Duramax
2011 to 2016 6.6L LML Duramax
2017 to present 6.6L L5P Duramax Chevrolet Express
GMC Savana
Chevrolet Silverado HD
Chevrolet Kodiak
GMC Sierra HD
GMC Topkick
Hummer H1 Alpha
2011 to present
Ford F-Series Super Duty trucks (F-250, F-350, F-450) and Ford F-Series chassis cab 2015 – 2022
Ford F-Series medium duty trucks (F-650, F-750)
HorsepowerLow: 300 hp @ 3100 RPM
High: 445 hp @ 2800 RPM
Ford pick-up trucks
Low: 390 hp @ 2800 RPM
High: 475 hp @ 2800 RPM

Ford F-650, F-750
Low: 270 hp @ 2400 RPM
High: 330 hp @ 2600 RPM 

Torque


Low: 520 lb-ft @ 1800 RPM High: 910 lb-ft @ 1600 RPM
Ford pick-up trucks
Low: 735 lb-ft @ 1600 RPM
High: 1050 lb-ft @ 1800 RPM

Ford F-650, F-750
Low: 675 lb-ft @ 1600 RPM
High: 725 lb-ft @ 1800 RPM 

GM 6.6L Duramax vs. 6.0L Powerstroke

The 6.6L Duramax diesel engine launched a couple of years before Ford Motor Company and Navistar International launched the 6.0L Power Stroke diesel engine in 2003 for Ford Super Duty trucks, vans and sport utility vehicles. Much like later models of the 6.6L Duramax, the Navistar International 6.0L Power Stroke diesel engine was designed in response to increased emissions regulations. 

The 6.6L Duramax experienced engine issues over various versions, however not to the same extent as the 6.0L Power Stroke engine. Despite the advanced technology, the 6.0L Power Stroke diesel engine was regarded as one of the most problematic engines in the Power Stroke diesel engine brand line. Many of the issues with the 6.0L Power Stroke diesel engine stemmed from the emissions systems and/or lack of maintenance. Ford eventually canceled the manufacturing partnership with Navistar International due to the 6.0L diesel engine’s extensive recalls and warranty costs.

Feature comparisonGM 6.6L Duramax diesel engineNavistar International (Ford)
6.0L Power Stroke diesel engine
Production years2001 to 2004 6.6L LB7 Duramax
2004 to 2005 6.6L LLY Duramax
2006 to 2007 6.6L LBZ Duramax
2007 to 2011 6.6L LMM Duramax
2011 to 2016 6.6L LML Duramax
2017 to present 6.6L L5P Duramax

Chevrolet Express
GMC Savana
Chevrolet Silverado HD
Chevrolet Kodiak
GMC Sierra HD
GMC Topkick
Hummer H1 Alpha
2003 to 2007 Ford Super Duty Trucks
2003 to 2005 Ford Excursion SUV
2003 to 2012 Ford E-series vans & chassis cabs
HorsepowerLow: 300 hp @ 3100 RPM
High: 445 hp @ 2800 RPM
Low: 325 HP @ 3300 RPM
High: 350 hp @ 2600 RPM
TorqueLow: 520 lb-ft @ 1800 RPM
High: 910 lb-ft @ 1600 RPM
Low: 560 lb-ft @ 2000 RPM
High: 570 lb-ft @ ,000 RPM  (2005 to 2007 models)
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