Best Duramax Engine – Which Is The Greatest Duramax Diesel?

by Conner Mckay

Are you planning on purchasing a Chevy truck and you are looking for the best Duramax engine out there? Well, if that is the case, then you are at the right place because there will be a lot to cover when it comes to the different Duramax generations and learn everything about them.

Having the choice of picking between a Cummins and a Duramax can be really difficult because they both are excellent engines and if you chose to get a Duramax then you are on the right track, to be honest.

These engines were perfected throughout the years that have become a benchmark when it comes to diesel engines for trucks. But unlike the Cummins which comes in different variations, the Duramax mainly comes as a V8, which is the 6.6 Duramax.

This means that this is a 6.6-liter engine that is included in a ton of different General Motors models. Even though the Duramax badge also has a straight-6 and straight-4 engines. But more on that later on in the article.

First, we are going to learn what is a diesel engine and how diesel works. Then we will learn more about the Duramax engine and then we will dive into the Duramax generations where we will focus on the 6.6 Duramax engines and cover their specs and also their problems. So, if you want to learn more, follow along till the end.

What Is A Diesel Engine?

Now let’s cover some of the basics here before we dive into the best Duramax engine. Let’s learn what is a diesel engine in general. I bet that there are a ton of people reading this article who are not into cars and want to learn what is a diesel engine and how a diesel engine works. So, the following chapters are for them. If you feel like you are up to the task you can jump to the Duramax generations. If not, keep up with us for a bit.

So, what is a diesel engine? A diesel engine is an internal combustion engine that is designed for heavy-duty use. In the car world, there are two types of engines that are mainly used based on the fuel that they use. These two types are gasoline and diesel.

Gasoline is used purely for horsepower and the speed that it can squeeze out. While the diesel engines are used for torque. As we all know, torque is one of the most important aspects when you plan to get an engine for towing like in our case with the Duramax.

Diesel engines have really high low-end torque which makes them perfect for towing heavy stuff. What a diesel engine can pull off is not comparable to any gasoline engine. Even if both of them are the same size and displacement engines. Diesel simply works much better.

Plus, diesel is a lot more friendly to your wallet. Diesel engines spend less fuel and deliver more power. But have you asked yourself how diesel engines work behind the curtain? What makes them so special on the inside? Let’s elaborate more on this before we learn more about the best Duramax engine.

How Does Diesel Engine Work?

Now let’s learn how a diesel engine works before we learn more about the best Duramax engine. Knowing how a diesel engine works will help you understand why you need one for yourself. So, how do these diesel engines work?

Well, the diesel engine as you probably know is using diesel fuel. This type of fuel is a lot different in comparison to your standard gasoline.

Diesel is much denser and less flammable than gasoline. So, igniting this type of fuel is a real challenge.

This is why the whole ignition system on a diesel engine is a lot more different in comparison to the gasoline engine. On gasoline engines, you have your standard spark plug ignition system. But in diesel engines, you don’t have spark plugs.

Diesel fuel is ignited by compression. The fuel is compressed so much that it ignites by itself. So, the compression ratios in these engines are crazy high.

This is why the engine blocks and cylinder heads are always made of cast iron because if they are produced out of aluminum, they would simply crack under the high pressure that is applied. This high compression ratio is giving the diesel engines that low-end torque that is needed when it comes to towing stuff.

Also, almost all modern diesel engines are turbocharged. By using forced induction, carmakers found a way to make these engines perform on par with the gasoline engines, and basically, you will not be able to tell the difference between the two of them like in the past when diesel engines were extremely slow. But what is the best Duramax engine? We will get to that in a bit after we learn what is a Duramax engine.

What Is A Duramax Engine?

Now before we learn more about the Duramax generations, let’s first learn the basics of what is a Duramax engine? Knowing this will help you understand in which vehicles these engines were included.

Duramax is a company that is a joint venture between General Motors and Isuzu. We all know Isuzu and their high-quality diesel engines, so GM decided to form a joint venture with them and create a series of engines for their trucks and SUVs. And that’s how Duramax was born.

Duramax was founded in 2001 and the first engine was the best Duramax engine, the 6.6 Duramax that we are covering in this article. And believe it or not, this engine is still in production to this day.

Even though there are a number of different generations that implemented a lot of changes and upgrades. We can say now that this engine is fine-tuned to perfection. Although the first generations were not that bad at all when it comes to performance.

Another thing worth noting is that the Duramax engines are assembled in Defiance County, Ohio, which makes them all American engines. And they can be found on a ton of Chevrolet and GMC trucks. But more on that later on, now let’s discuss the generations of the 6.6 Duramax and learn which is the best Duramax engine out of the bunch.

Duramax Generations

Now let’s cover the generations of the best Duramax engine. It is worth noting that there are six generations of the Duramax engine in total.

All these generations are based on the same block which is the Duramax 6.6. But there were slight changes when it came to horsepower and other important aspects.

Luckily for you, we are going to cover all of these generations and learn more about which one should you go after when looking for a new truck. So, follow along till the end.

First Generation Duramax Engine LB7 (2001 – 2004)

Now let’s begin covering the first generation of the best Duramax engine which is the LB7. The LB7 was the original Duramax engine produced between 2001 and 2004.

This engine like all of these engines is a V8 with 6.6 liters in displacement. It implemented a cast-iron block that was really tough and this is why people are still after these engines and want to get one for themselves. But what about power how much horsepower does this engine make?

This engine produced about 300hp and about 520lb-ft of torque. Which was plenty for towing at the time. Not comparable to modern applications but still respectable.

This engine was included in a lot of GM vehicles. Namely Chevy and GMC trucks such as the Silverado, Sierra, Kodiak, and Topkick. But what about the common problem with the best Duramax engine?

LB7 Duramax Problems

When it comes to problems, it is worth noting that this engine suffers from a few issues. The prime problem with the engine was the issue with the fuel injectors. A lot of trucks had problems with the original injectors.

Other problems included fuel filter housing O-ring leaks, water pump failures, head gasket failures, overheating issues, and issues with the Allison transmission. This engine had more issues and cannot be considered the best Duramax engine. And we would advise you to avoid it if you can and go for something newer.

Second Generation Duramax Engine LLY (2004 – 2005)

In 2004 the new generation of the best Duramax engine was introduced, which was the LLY. The LLY was a slight upgrade over the LB7 and improved much on the predecessor’s downsides.

This engine kept the same core concept and much of the mechanical components but it offered some improvements as we mentioned.

Major improvements were implemented on the injectors since the ones on the early models failed at a rapid pace. Then the valve covers were also improved and these improvements have allowed good access to the injectors without even removing the valve cover.

When it came to power, the numbers were slightly improved. The LLY produced about 305hp and 590lb-ft of torque.

Similar to its predecessor the LLY was included on the Chevy Silverado and GMC Sierra. But what about the problems with the best Duramax engine?

LLY Duramax Problems

Despite this model of the engine being heavily upgraded from the predecessor. It still has its shortcomings. This engine still has problems with the head gaskets and water pump malfunctions.

There are also other problems like the lacking of a lift pump which is quite an essential component. Along with these issues, there were turbo inlet manifold failures, problems with the injector harness, problems with glow plugs (for more insight, check out our guide on how many spark plugs does a diesel have), EGR issues, and bent rods. Overall, this engine is also not the best Duramax engine.

Third Generation Duramax Engine LLY/LBZ (2006 – 2007)

The third generation of the best Duramax engine had two VINs. The first is the LLY VIN2 which is a slightly de-tuned engine that produces only 250hp and 450 lb-ft of torque.

While VIN D also known as LBZ was the more potent variant which produced about 360hp and 624 lb-ft of torque. And when it comes to these years, the LBZ is probably the engine that you want since it is a potent engine that is more powerful than the basic LB7 and the LLY.

This engine was heavily upgraded to improve its durability. More precisely it saw big upgrades on the connecting rods and rod bearings. And this engine was also made quieter than the previous generations.

This engine was also included in the Silverado, Sierra, TopKick, Kodiak, and the Hummer H1 Alpha.

Many people are thinking about LLY vs LBZ and we would recommend you to go for the LBZ. Mainly because it is more powerful and overall a better engine.

LBZ Duramax Problems

This is easily the best Duramax that we covered until now and is also the best when it comes to durability.

Still, it has problems with cracked pistons, EGR problems, glow plug issues, water pump failures, and issues with the Allison transmission leaks.

Fourth Generation Duramax Engine LMM (2007 – 2010)

The fourth generation of the best Duramax engine was greatly based on the previous LBZ. It implemented the same compression ratio and implemented a cast-iron block with an aluminum head.

When it comes to power, it is worth saying that this engine produces about 356 hp and 660 lb-ft of torque. Which is rather good and one of the highest horsepower Duramax engines to this date. It included a better cooling system and better fuel management software as well.

Another novelty was the Diesel Particulate Filter, also known as DPF. This component greatly decreased the pollution caused by the best Duramax engine.

It was used in the Chevy Silverado, Chevy Express, GMC Sierra, and GMC Savanna.

LLM Duramax Problems

The first and major problem with this generation of the best Duramax engine was the problem with the new DPF filter on the trucks (just make sure you’re not seeing a P2002 error code). These filters produced problems such as clogging up and other DPF issues.

Other problems included leaking transmission lines, low fuel pressure, problems with the pistons developing cracking, and crankshaft failures. These were rare though and not something that important to scare you from buying the best Duramax engine.

Fifth Generation Duramax Engine LML (2011 – 2016)

The next best Duramax engine that we are going to cover is the LML Duramax engine. This engine is easily one of the most powerful Duramax engines out there.

This engine implements the same compression ratio as the previous generation. The LML produces a whopping 397hp and 765 lb-ft of torque which are quite respectable numbers.

This engine implements the DPF system plus a new feature known as Diesel Exhaust Fluid Injection also known as DEF. These two systems reduced the Nox gas release by up to 63% in comparison to its predecessors.

This generation also included other big improvements in comparison to the previous generation of this engine. These were some minor tweaks such as an upgrade in the casting of the block, a new water pump that solved most of the problems from the previous generations, a new main bearing design, and also a re-routed oil passage.

All these changes greatly improved the power numbers and raised the horsepower ratings close to 400hp. So, this is arguably one of the best Duramax engines out there. But what about the problems? Let’s elaborate on them next.

LML Duramax Problems

The LML also has a fair share of problems as well. These problems are mostly concerned with the DPF and DEF emission systems.

Overall, all these trucks produced during this era have these problems. So, regular DPF cleaning and maintenance is essential in order to avoid expensive problems.

Sixth Generation Duramax Engine L5P (2017 – Present)

Now let’s cover the best Duramax engine which is the L5P. This engine is produced from 2017 and up until this day.

This engine is a step ahead of the previous LML and includes some substantial improvements to the block and rod bearings. Making it much more durable than the previous generation.

And we can see that by the numbers. The L5P produces about 445hp and 910 lb-ft of torque. Which are crazy numbers for a diesel engine.

This engine also implements a ton of upgrades on the turbocharger, and improved cylinder head casting designed to bring more performance. It also implements a new air intake system with a hood scoop in addition to all this.

This engine comes on the Chevy Silverado and GMC Sierra as all the previous generations from the same engine. But what about the problems with the best Duramax engine? Let’s explain them next.

L5P Duramax Problems

When it comes to the problems with this engine it is worth that are no major issues present. So, you don’t have to worry much.

These are still new engines and rarely produce problems. Some of them though have some minor problems with the Allison 1000 transmission, problems with the MAP sensor, and fuel injector problems. Overall, that’s everything you need to know when it comes to the issues? But what is the best Duramax engine? Let’s see next.

Best Duramax Engine

So, what is the best Duramax engine? Well, we can easily say that the L5P is the best out of the bunch. Why is this the case? Mainly because this engine is fairly new and also there are no major problems reported with it.

Still, this doesn’t mean that there are no issues at all with this engine. There are some problems with the L5P engine as well but they are minor ones.

Best Duramax Engine

Also, the LML is another great engine that delivers an excellent performance. It has some troubles with the DPF and the DEF but they are common on all trucks from this era.

If you want a real bulletproof engine with no emissions devices such as the DPF. We would recommend you the LBZ engine. This engine produces a ton of horsepower and is also able to do much more than this if you do some minor tweaks to it like a cold air intake.

So, we learned what is the best Duramax engine. But what are the Duramax years to avoid? Let’s learn more about that next.

Duramax Yeas To Avoid

So, we covered the best Duramax engine and we learned that this engine is the L5P. But what are the worst engines and the Duramax years to avoid?

Well, we can easily say that the worst years are the first four years between 2001 and 2004. These are the years of the LB7 engine. This engine was not perfected and had a number of issues with the water pump, fuel injectors, head gasket failures, and more.

Also, the LLY which is an upgrade of the LB7 is not that big of a change from the previous LB7 model. So, the best thing is to avoid all of the years from 2001 to 2005.

Models after 2005 have a number of improvements in terms of durability as well as better power output. So, you should go after these engines in our opinion. This way you will be sure that you don’t end up with a money pit full of problems.

And frankly, these early engines have seen a lot throughout their lives and went through a ton of repairs and issues. So, they are definitely not the best Duramax engine.


In this article, we have covered quite a bit when it comes to the best Duramax engine. First, we learned what is a diesel engine and how diesel engines work.

Then we learned more about the best Duramax engine. We covered all the generations of this engine and their upgrades and problems. Lastly, we learned which engine is the best and which engines you should avoid when purchasing a GMC or Chevy.


Now let’s answer some frequently asked questions.

What Is A Duramax

Duramax is a joint venture between GM and Isuzu. This company produces diesel engines for the American market. These engines are used on Chevrolet and GMC products like the Chevy Silverado and the GMC Sierra.

Who Makes Duramax

General Motors along with Isuzu are making Duramax diesel engines. The Duramax engines are designed and manufactured in the US. More precisely in their Ohio plant. So, Duramax engines are all-American.

What Is The Best Duramax Engine

The best Duramax engine is the L5P. This engine is the most advanced out of the many that were released throughout the years. This engine is also the most potent one producing more than 910 lb-ft of torque. Great engine for hauling or towing stuff. It is also quite more expensive. But understandably, quality costs.

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