The Chevy Duramax Years To Avoid

You just spotted a beautiful Duramax, and you’re tempted to stop and make an offer, but should you? Here are the Chevy Duramax years to avoid and why.

Despite the popularity of the Duramax engine, the early versions struggled for years. The worst years of the Duramax are 2001 – 2010. Although GM introduced four diesel motors during these years, they all had severe issues, including overheating, fuel problems, and cracked pistons when stressed. 

When the Duramax debuted in 2001, GM tried to counter the Ford Powerstroke engine that had dominated the diesel market for years.

The Duramax replaced the 6.2 and 6.5 V8 engines and was developed as a joint venture between GM and Isuzu. 

Over the years, the engine has undergone numerous upgrades and design changes due to severe performance issues (especially with early models), but since 2011, the Duramax engine has improved dramatically. 

Even though it took GM about a decade to get the engine right, the current result, the L5P, is considered an excellent and reliable diesel engine. 

What Are the Major Issues with the Early Duramax Engines?

As mentioned, the early years of the Duramax engine were fraught with problems. Many owners found the engine strong and capable but also filled with problems. 

We have listed the early engines below with some specifics about why we recommend avoiding them. For more information about which years of Duramax to avoid, see the article on fourwheeltrends.com

2001 – 2004 6.6L – LB7

The LB7 engine reached the 2001 – 2004 Chevy Kodiak, Silverado, GMC Topkick, and Sierra HD. Without question, the first edition of the Duramax sprang life into sales for GM for a few years. 

However, when the vehicles reached the 100,000-mile mark, the engine began to suffer from several issues. 

Injector Failure

Customers complained of the truck smoking while idling fuel in the oil (owners often checked oil levels only to be greeted with the smell of fuel on the dipstick). 

The only solution was replacing the faulty injectors, which often was a full-blown job involving major engine work and a repair bill of nearly $3000. 

GM recognized the issue, corrected it in the next edition of the Duramax engine (LLY), and offered an extended warranty on the engine for 200,000 miles or seven years, whichever came first. 

Leaking O-rings on the Fuel Filter Housing

As the Duramax gets driven for a while, the O-rings on the fuel filter housing tend to deteriorate and become less pliable. While the repair wasn’t expensive, it was a hassle to take the truck in and have it done. 

Because the air was often getting into the fuel system, the result was an improper mix moving into the chambers and the truck running cold or being challenging to start after sitting. 

2004 – 2005 6.6L – LLY

The LLY engine was found on the Chevrolet Silverado, GMC Sierra, and Hummer H1.

Overheating Issues

The LLY tended for the engine to overheat. The problem stemmed from an inadequately sized radiator which wasn’t large enough to perform what many owners asked their trucks to do. In addition, the engine frequently suffered from busted head gaskets, experienced fan clutch failure, or even had, at times, water pump breakdowns. 

2005 – 2007 Duramax LBZ

The LBZ version of the Duramax engine was placed in Chevy Silverado HD and the GM Sierra HD, among other vehicles. While the engine produced significant horsepower and torque (360 HP and 650 lb/ft of torque), it was still ripe with issues. 

Cracked Pistons

Many owners were excited about the increase in power and modified trucks. Unfortunately, the pistons couldn’t handle the extra stress and often cracked under the pressure of heavy lifts. 

Even though the engineers redesigned the block to withstand more power, they left the pistons alone and created the situation of the pistons failing. (The pistons were cast iron, prone to breaking).

Other Issues

As if a cracked piston isn’t bad enough, the LBZ suffered from faulty glow plugs, the usual water pump issues, and transmission leaks from the Allison 1000 tranny. 

Owners detected leaks from their trucks every 20 – 30k miles, leading to massive frustration. 

2007 – 2010 6.6 LMM Duramax

The LMM was designed with increased emissions regulations coming into play for diesel engines. The unit was installed in the Silverado HD and Sierra HD, along with other V8 candidates. 

Initial reports were positive, as the Duramax outperformed the Ford 6.4 Powerstroke and the 6.7 Cummins found in Dodge trucks, but eventually, the true nature of the engine came to light. 

DPF Failure

The LMM added a diesel particulate filter (DPF) to the exhaust system, which tended to get clogged. 

GM tried to develop a system to keep this from happening (where the exhaust “regenerated” continually), but it didn’t work half the time. And as anyone who drives a diesel truck knows, there is nothing like a clogged exhaust to wreak havoc on cooling systems and engine performance. 

While most DPS systems can be cleaned, the frustration with the LMM system was that most engines required DPS replacement. 

The cost was often a ton of money, from thousands to close to ten thousand, depending on how much damage had been done to the engine.  As you can imagine, owners unhappy with the new emissions systems were even less thrilled when they did not work correctly.

What About the Duramax After 2011?

The Duramax engine was redesigned in 2011 in response to stringent emission controls placed on diesel engines by the government. Since then, the Duramax has seen several updates and modifications, but the engine has generally stood the test of time and produced far fewer mechanical issues. 

What are the Best Years of the Duramax Engine?

There’s a bit of debate about which Duramax engine is the best. Many purists love pre-2007 engines due to the lack of emission controls. 

Newer models have more power and torque and fewer mechanical issues. For more information on the best years, see the article on fourwheeltrends.com.

In 2017, GM produced the safest Duramax engine, the L5P. It has the best power and torque (445 HP and 900 lb-ft of torque). It also produces the best fuel economy. Since diesel engines are designed to last over 250,000 miles, it is easy to see how fuel and maintenance savings might add up over the life of the truck. The L5P is found in Chevy Silverado HD and GM Sierra HD models from 2017 to the present.  

While the L5P has some issues, with the MAP sensor getting fouled up, this is one of the few customer complaints about this engine.

At the same time, the L5P is still relatively young (as far as diesel engines go), but so far, so good. If you are considering purchasing a Duramax, we recommend choosing one of the more recent models to save some aggravation and keep your new truck out of the shop. 

Key Takeaways

• The worst years of the Duramax engine are the 2001 – 2010 models.
• The most common issues with Duramax are cracked pistons and water pump failures.
• The safest choice in a Duramax is the L5P, found in 2017 to present models. 
• The estimated life of a diesel engine is 250,000 miles or more.