Duramax years to avoid — most common problems

Going for a truck with a diesel engine is pertinent if you need a vehicle with lots of versatility and power. There has been a 28 percent increase in the number of diesel vehicles sold in the United States, with most of these engines from General Motors, one of the most popular diesel vehicle manufacturers.

The Duramax diesel engine is one of the primary motors in a General Motor (GM) truck. While these engines are reliable and durable, a few model years have specific problems you would want to avoid.

This article gives detailed information on Duramax years to avoid down to the best Duramax model years you can consider buying and also provides answers to related questions.

Why you can trust REREV’s advice on which car model years to avoid: Our car experts look at official data, ask real drivers what they think, and talk to experienced mechanics to make sure our list is useful. This reliable info can make buying a car easier for you. Want to know how we do it? Find out more about our research methodology.

Most common Duramax problems

There are several issues associated with the Duramax engine. These problems are usually associated with the fuel injector, fuel injector harness wiring, water pump, engine overheating and blown head gaskets, etc. We’ll go through these problems one after another down below.

Duramax fuel injector failure

This problem is prevalent with the LB7 Duramax model years. Although General Motors recalled these engines and gave them a seven-year and 200,000-mile warranty, its fuel injector remained a significant problem. The exact problem with the fuel injectors is that they functioned underneath the valve covers.

When diesel leaks occur, it dilutes the oil supply, causing the main bearing to fail. The revised LLY version, released in 2004, had externally-located fuel injectors. This was an advantage as it made servicing the injectors much easier and allowed ease when doing a visual inspection.

Glow plugs

Glow plugs heat fuel and air to improve your engine’s combustion efficiency. When your glow plugs begin to fail, you may experience problems like decreased fuel efficiency. Your truck may also exhibit rough idling, engine misfiring, or hard starting. Your exhaust may give off certain signs that could point to this problem. If your exhaust gas assumes it is white or black instead of the regular thin and gray, you might have a glow plug issue just sitting around the corner.

Although not all Duramax models are faced with glow plug issues, you want to be on the lookout if you have a 2006 model. The 2006 LBZ and LLY models are known for their glow plug problems causing GM to recall them.

Fuel system

While most known Duramax problems affect specific model years, the faulty fuel system is an issue that plagues all model years. It usually starts with difficulty starting the vehicle and then transits to excessive smoke, poor fuel economy, lower RPMs, loss of engine power, and excessive noise.

While there are several fuel system problems out there, the 6.6L Duramax is known to have two consistent issues. First, the 6.6L Duramax uses an injection pump instead of a lift pump, and this can cause cracks in the fuel filter housing. Secondly, with its type of engine design, air can quickly get into the fuel lines, thus preventing sufficient fuel from reaching the engine.

Water pump

Water pumps wear out depending on how long you’ve driven the vehicle. You can expect to drive up to about 100,000 miles or more for an average diesel engine before you bother about a water pump replacement. Unfortunately, driving a Duramax engine may need a water pump replacement at around 80,000 miles.

Some new drivers may need help understanding why a water pump should be a big deal. However, a damaged water pump indicates that there won’t be enough coolant supply to your engine, thus causing it to overheat. An overheated engine is a nightmare no driver wants to have, and you would need to stop your vehicle as often as it overheats to allow it to cool down.

Overheating can lead to severe problems like damaged cylinders or pistons, cracked engine blocks, and blown head gaskets. Since you know that your Duramax engine is prone to water pump failure, you need to look for possible problems.

You should have a trusted mechanic check out your cooling system if you notice overheating, coolant leaks, signs of corrosion on your water pump, or whining noises from the front of your engine.

Fuel injector harness wiring

This issue is common on the LB7, LLY, and later models. This concerns wiring in the fuel injector harness system that chafes, leading to broken or shortened circuits. Your vehicle may throw off symptoms like rough running or no-start if you experience this problem. 

Specific injectors affected by this problem usually give off an “open circuit” code. Moving the wires to an individual injector allows them to work correctly for a while -this can be useful if you need to run a quick diagnosis. You can repair this by reconnecting or insulating the affected wire(s).

Oil

Oil issues are never a good thing to experience, and in Duramax’s case, the problems go all the way into the turbocharger. Generally, when worrying about oil leaks, you may only be thinking of oil leaking out of your engine. In the 6.6L Duramax particularly, there is a more critical problem. The oil leaks into the turbocharger, coating its interior and exterior components.

The problem is caused by a faulty PCV design -a properly functional PCV should send out waste gasses from the crankshaft and prevent other gasses from entering. However, this isn’t the case, as Duramax’s defective PCV design does the exact opposite by allowing oil into its turbocharger. This can lead to more serious engine damage that would require expensive repairs.

Which Duramax years to avoid?

There are great Duramax engine models out there for you to try; however, there are specific model years that you should avoid. Below, we give a rundown of these years to avoid.

Duramax LB7: 2001-2004 model years

As the first Duramax model to be released, the LB7 is still very popular among diesel enthusiasts due to its lack of emission control parts. Generally, it is a very reliable and durable engine; however, once the first model hit the 100,000-mile mark, some issues begin unveiling themselves. Injector failure was prevalent on the LB7 engine.

GM acknowledged the problem by eventually adjusting the original design and offering a 200,000-mile warranty on the upgraded Duramax parts. When you buy a used LB7, it is crucial to find out if it still has its factory-installed injectors. If it does, you know you’ve got a replacement job to do in the future.

Other critical problems that you should expect on the LB7 include the following:

• Fuel filter housing O-rings leaks
• Water pump leaks
• Overheating
• Head gasket failure
• Lack of a factory lift pump

Duramax LLY: 2004.5-2006 model years

GM only produced the Duramax LLY engine for a short time. It was almost identical to the LB7, with emissions control parts still absent. GM had resolved the injector problems by the time the LLY engine was released. Instead of injector problems, the LLY had overheating issues when driving in hot temperatures or towing heavy loads. The stock air intake system of the engine caused this.

Its original turbo mouthpiece was too narrow, thus contributing to the engine running hotter. An excellent fix is using Duramax aftermarket parts like a cold air intake and an aftermarket turbo inlet. Other issues with the LLY included the following:

• Injector harness chafing
• Water pump failure
• Glow plug failure
• Fuel pressure relief valve
• Lack of factory lift pump
• EGR valve issues
• Head gasket failure

Duramax LBZ: 2006-2007 model years

The LBZ is generally considered the best Duramax engine built. It is given this designation owing to the following reasons:

• First Duramax to come with a 6-speed Allison transmission
• Lack of emissions control parts
• GM worked out the issues of the previous engines

For the most part, the LBZ didn’t have much of a problem, and the main issue was the need for a factory lift pump. Fortunately, it is a Duramax diesel part that you can install without spending much money. Expert tuners found the only minor issue it had to be its pistons cracking if you tried modifying its horsepower to exceed 600hp.

Duramax LMM: 2007.5-2010 model years

The premiere of the Duramax LMM engine coincided with new requirements for emission control parts. Mechanically speaking, the Duramax LMM was almost the same as the LBZ, but with emissions control parts that weren’t present on the LBZ. That was one problem point, but another concern was with the pistons.

As mentioned earlier, excessive modifications to get more than 600hp on the LBZ can cause its piston to crack. However, the LMM pistons would break even faster if you attempt to modify it beyond 600 horsepower; this was due to its injector setup.

The LBZ had seven fuel-spray holes, while only six were available on the LMM; this means that two fuel streams came out in opposing directions over the piston wrist pin. This causes hot spots to build on the weakest part of the piston, which may result in a crack.

Best Duramax years

The Duramax can be an excellent engine for your truck if you avoid the model years above and stick to its durable and reliable ones. Below, we give a list of these reliable models you can pick.

• 2010 – 2017 Duramax LGH
• 2011 – 2016 Duramax LML
• 2011 – 2021 Duramax XLD25
• 2012 – 2021 Duramax XLD28
• 2014 – 2021 Duramax LWN
• 2017 – 2021 Duramax L5P
• 2019 – 2021 Duramax LM2

The LML was rebuilt for its debut in the 2011 model year. The power for this model year was increased to almost 400 hp and 765 lb of torque. GM had to raise the fuel system pressure to achieve this type of power without compromising emissions; unfortunately, this took a turn on the injection pump.

The only downside to this engine’s sudden fuel pump failure is that it caused a large number of shaving to spread throughout the fuel system, contaminating the entire system. To fix this, you need a new fuel system, which includes a pair of new fuel rails, high and low-pressure fuel lines, injectors, a new pump, and fuel filters. You’ll also need to drop the tank to clean the metal debris thoroughly.

You can prevent this problem by installing a lift pump that would provide better filtration for debris and air. Many drivers who own the LML usually install the older Bosch CP3 that was first used in the LB7 engine. Although it has a slightly lower pressure, it can still carry more horsepower.

The L5P is generally thought to be the best post-emissions Duramax engine, and GM fixed all the issues that plagued the emissions system and injector pumps in previous models. Mechanically, the engine is reliable, and owners have reported a few problems.

The common problem with the L5P is that its MAP sensor becomes clogged with soot, thus triggering a check engine light. This is an easy problem; install a MAP sensor spacer and clean off the soot with an electrical cleaner.

The Duramax LGH, Duramax XLD25, Duramax XLD28, Duramax LWN, and the Duramax LM2 go a step further in providing better emissions, thanks to the diesel fluid/urea injection feature installed on them. Also, with the help of exhaust after-treatment, owners can increase their trucks’ fuel economy.

The only problem owners complain about is weak tie rods that may get damaged when off-roading, sled-pulling, or drag racing. The exhaust after-treatment system/diesel particulate filter also presents a failure point that may cause problems.

Is Duramax worth buying?

Duramax engines can be an excellent choice for your truck if you only stick to safe and reliable models. Although these models are not perfect, they present a lower chance of troubleshooting, allowing you to enjoy your engine for over 300,000 miles -although consumers have reported having their Duramax engines last up to the 500,000 miles range.