duramax , diesel , LB7 , Gm , silverado , sierra

Everything You NEED to Know About The LB7 Duramax

Everything You NEED to Know About The LB7 Duramax

There’s nothing quite like the original, and that’s exactly why the Duramax LB7 is one of the most notable diesel engines in the history of the Silverado / Sierra HD lineup. This motor is the first diesel to be called a “Duramax”, and it is the first product of the partnership that formed between Isuzu Motors Ltd., and General Motors.

The LB7 represented a long sought-after need in the HD lineup for an engine that was about the same displacement of the large gas engines in the lineup but produced the kind of torque and fuel efficiency that’s expected from a diesel.

Although a bit notorious in their own ways, the Duramax was a huge step in the right direction for GM and would go on to serve as the inspiration and foundation many generations after.

We’re going to cover everything you need to know about the Duramax LB7:

  • Origin Story
  • Engine Specifications & Tech Dive
  • LB7 Reliability
  • Performance Upgrades

Origin Story

To really understand the LB7, you need to understand the how and the why of where it came from, and why it ever came to be in the first place.

The Duramax line of diesel engines came out of the joint - partnership between two automotive titans: General Motors and Isuzu. Now, the history of these two brands actually goes back way farther than the Duramax, with origins starting back in 1972 when General Motors was looking to partner with a manufacturer to bring small, fuel-efficient vehicles to the United States in the post-oil - crisis world.

To be blunt, GM had a very hard time turning the corner from the muscle car era 1960s, and Isuzu was already in the business of making small fuel-efficient vehicles - it just made sense.

The First GM / Isuzu Product - The Chevrolet LUV

Times in the ’90s were good for both GM and Isuzu, and GM decided it was time to put more focus on Diesel technology, specifically for their lineup of medium and heavy-duty trucks. Isuzu were experts in diesel technology and held several patents and a deep engineering experience of diesel-powered knowledge. Although GM had dabbled in diesel before, it was never quite successful.

1997 would see the formation of DMAX Ltd., an engine manufacturer built from the ground up as a joint partnership between GM and Isuzu. 49% of the company was owned by GM, and the rush was on to not only develop a medium / heavy duty diesel powerplant but to build a factory that would mass-produce this engine. In a mere 37 months, Dmax had not only developed a new engine but built a state-of-the-art factory in Moraine, Ohio that could produce 100,000 engines a year. Wow!

Sales for Isuzu peaked in 1996, with the popular Rodeo SUV and Hombre pickup leading the charge but, a mere 10 years later, the company had effectively ended operations in the United States! Aging vehicles and several failed vehicles launch (Vehicross, we’re looking at you) saw the steady decline of Isuzu sales become ever more looming. Subaru bought out their Indiana plant in 2002, and after some serious restructuring, GM ended up with an even bigger stake in the Duramax at 60:40 that stands to this day.

LB7 Engine Specifications & Tech Dive

Engine Specifications

In 37 months, Dmax LTD had a clean-sheet design that was designed to fit cleanly in the engine bay of a GM’s Heavy Duty (HD) pickup line. Since Diesel engines run equipment like turbochargers, intercoolers, oil coolers, and fuel rails - packaging a diesel engine to fit in the same space as a gasoline engine would be a huge challenge.

To accomplish this, the LB7 nestles this equipment in the valley of the engine. The oil cooler was attached directly to the left side of the cylinder block and includes a clever cooling system to adequately maintain temperatures on both sides of the engine. Auxiliary equipment was attached to the front of the engine and driven via a serpentine belt for ease of installation and service.


Cast from a unique gray iron alloy, the LB7 utilizes a “deep skirt” design that beefs up rigidity. Bearing caps are connected to the lower part of the block with main bolts and reinforced with two side bolts as well. The upper two inches of each cylinder bore were also induction hardened to resist cylinder wall wear over time and were treated to a specific process that ensured the cylinders were not only perfectly round but squared up to the deck surface perfectly.

Rotating Assembly & Top End

The internal components on the LB7 were designed to be lightweight, yet extremely durable. Cast in 4340, the crankshaft was treated with a process to increase durability under extreme heat. Lightweight cast - aluminum pistons (among the lightest ever put into a Duramax engine).

Forged steel connecting rods with a cracked cap design ensure utmost durability, even under high horsepower loads. Aluminum heads housed a 4 valve per cylinder design, while 6 torque to yield bolts per cylinder provide optimal pressure to ensure proper combustion sealing.

Turbo & Fuel System

A fixed geometry turbo supplied by IHI was installed on the LB7, marking the only fixed geometry unit ever used on a Duramax. Going against the grain, the LB7 was not designed with a lift pump and instead utilized a high-powered CP3 fuel injection pump from Bosch to pull fuel into the common rails for storage at high pressures. This pioneering design (now common on diesel engines) led to some teething issues (more on that later) and worked along with a solenoid style injector.

LB7 Reliability

When it comes to overall reliability, the LB7 (short of these issues) was pretty damned reliable for a first-generation engine. Credit goes to the team at Isuzu, since they knew a thing or two about building highly durable, commercial grade diesel engines that are found in applications all over the world.

Here are some of the most common issues seen on the LB7:

Fuel Injectors

We mentioned above that Diesel Direct Fuel Injection technology was essentially pioneered on the LB7 and well, that led to some major issues with the fuel injectors on this motor. Two main issues were prevalent:

1. Over time, the internal components on the injector (ball seat) would wear out, and then leak fuel.

2. Injectors would crack, leading to air/fuel issues.

GM realized this was a huge issue, and completely redesigned the injectors and offered a special warranty of 7 years or 200,000 miles for all replaced injectors.

Even replaced factory injectors tend to fail and an upgrade to a high-quality aftermarket injector is always recommended.

Head Gasket

Due to a flawed design on the head gasket, over time, failure is almost an inevitability. The issue comes down to a crimped design that formed a sort of containment ring around the cylinders, but this design gave in to pressure over time and allowed the layers of the gasket to separate. Again, GM realized this was a major issue and redesigned the head gasket with a layered steel design that ditched the crimped edge containment design.

A quality head gasket replacement kit should include not only the gaskets themselves but all everything to get the job done right.

Fuel Filter Housing O-Ring Leaks

Over time, the O - rings around the fuel filter housing on the LB7 can fail, causing leaks. Upgrading this component with a quality aftermarket kit will decrease the likelihood of leaks and reinforce this common fail point on the LB7.

Trust The LB7 Duramax Experts

Whether you’re looking for a complete fuel injector replacement kit or the best in lubricants, and additives for your LB7; Merchant Automotive has you covered with the best products, at the best prices. We’re experts in this unique motor and we’ve got thousands of hours of practical experience under our belts that makes us the experts you want on your side when getting to work on your personal LB7.

Whether you’re running a stock set - up or you’ve upgraded your LB7 to be a drag-racing or pulling monster; Merchant has you covered.

Check out our full - selection of LB7 parts and accessories today!

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