3.0L LM2 Duramax: Everything You Need to Know

About two or three weeks ago, we put an article talking about Duramax engines and we went through every engine from the LB7 up to the L5P. We even covered some of the history before that with the 6.2L and 6.5L Detroit Diesel engines, but, we didn’t cover the new small Duramax engines.

So for that reason, and the fact that I think this engine is more interesting than other 3.0L diesel engines that you’ll in half-ton trucks, we’re going to take a deep dive into the GM LM2 and tell you everything you need to know. So, get comfy, and let’s get into it.


Other than the name, the 3.0L inline-six has little in common between the 2.8L I-4 Duramax found in the Colorado/Canyon and the 6.6L V-8 Duramax under the hood of the 2500/3500 HDs.

“It is a clean-sheet design from the air intake down to the engine mounts,” said John Barta, assistant chief engineer for the new Duramax. “Very, very few common things were used from the other Duramax. We’ve optimized everything in this engine’s design to fit into the new-generation Silverados while incorporating advanced combustion and emissions technologies to optimize performance and efficiency.”

I think it’s also worth noting at this point that GM did not develop this engine on their own, it was actually a collaboration with Opel, the German automaker that GM owned until 2017, and the LM2 shared a similar architecture with two smaller Opel engines, but simply scaled up to an inline-six engine.

GM developed this engine for use in their half-ton trucks for the same reason that Ford, Ram, and Nissan also developed small diesel engines for their half-ton trucks: which is a gap in the market. If you wanted a diesel engine in your truck, you had no choice but to purchase a 3/4 ton or higher truck.

While those trucks are great at towing, hauling, and generally getting work done, they can also be quite a bit more expensive than half-ton trucks, physically larger, harder to drive, harder to park, they generally have stiffer suspension for heavy loads which leads to poor ride quality and on and on.

To put it simply, 3/4 ton trucks are generally not great daily driver trucks. While they’re much comfier and better than older trucks, most consumers would prefer to opt for a half-ton truck. So if you wanted a half-ton truck and you wanted a diesel engine, you were out of luck. There were really no options here in the US for that type of truck.

So, GM put together this engine, which is the LM2. It was designed for use in half-ton trucks and directly competes with Ram’s 3.0L EcoDiesel and Ford’s 3.0L Powerstroke. What makes this engine so much different as compared to the other 3.0L diesel engines on the market is that the LM2 uses a much different configuration.

While those other engines are designed as a V6 and a V8 respectively if you include the Titan XD 5.0L Cummins in the conversation, the LM2 is an inline-six, making it the only inline-six engine in this segment. There are a lot of benefits to using an inline-six configuration, especially in the context of a diesel engine, which is why you’ll typically find this configuration in commercial applications like semi-trucks, but we’ll get more into that later in the article.

So, starting with the basics, we’re looking at a 3.0L inline-six engine, with a 36,000 PSI common-rail injection system, an aluminum cylinder head with dual overhead cams and four valves per cylinder, an aluminum cylinder block with an 84mm bore and 90mm stroke, a compression ratio of 15:1, forged steel connecting rods, forged steel crankshaft, and hypereutectic pistons.

Other things worth noting are the ceramic glow plugs which aid in cold starts and reduce cold-start emissions, water-to-air intercooling, variable-length intake manifold, and all of that equals out to 277hp and 460lb-ft of torque.

Cylinder Head

To get into more detail, let’s start with the cylinder head and move our way down. As mentioned a moment ago, the LM2 features one large aluminum cylinder head. GM used aluminum because of its weight savings benefits and thermal benefits. Keeping the head cool has a big impact on performance and efficiency, plus since this engine was meant to be used in half-ton trucks, it needs to be quite a bit lighter in weight than the larger 6.6L Duramax engines.

Inside the head, you’ll find two camshafts, four valves per cylinder, 1.12″ intake valves, and 0.97″ exhaust valves. This engine flows from left to right, so you have the exhaust manifold on the passenger side of the truck and the intake manifold on the driver’s side of the truck.

With that, GM mounted the turbo very close to the head, which means very short runners leading to the turbo, which has some big benefits and a few drawbacks, but it mostly means quicker spooling turbo.

One of the more iffy parts of the LM2 is how the cams are driven, which is a rear-mounted system, meaning if anything happens with it or it needs maintenance, your transmission has to come off in order to access anything. On top of that, this whole system which includes the high-pressure fuel pump and both cams is all chain driven. For a lot of diesel enthusiasts, that’s a deal-breaker, because other engines offer a superior gear-driven system that is much stronger.

With this system, if the chain needs to be replaced, or the head pulled off the engine, or the high-pressure fuel pump needs to be replaced, it all means it’s way more difficult to complete those jobs because it’s rear-mounted instead of being at the front of the engine. You might be wondering why GM would do this considering all the downsides and it’s all centered around packaging.

You have to remember that although it’s a relatively small engine in terms of displacement, the inline-six configuration is much more difficult to package into an engine bay, especially an engine bay that was really designed around using V6 and V8 engines, which are much shorter in length as compared to an inline-six engine.

You have to remember, a V8 is really four cylinders long, whereas the inline-six is six cylinders long. The inline-six might be narrower, but its crazy length means you’re sandwiched between the firewall and core support. To help make this engine a little bit easier to package into their trucks, they stuffed the valvetrain chain and gears at the back of the engine instead of the front where it is on the large majority of engines on the market.

Moving on from the head, let’s quickly take a look at the intake manifold and the turbocharger.

Intake and Turbo

The variable intake manifold is one of the features on the LM2 that GM really pushed as a big selling point to show that this engine had more advanced features than what the competition was offering at the time the LM2 was released to the public. This is simply a dual pathway system with electronically controlled flaps, one per cylinder.

When the flap operates, it changes the path of the airflow, which leads to either a shorter or longer intake runner. This optimizes the airflow into the engine and improves performance and responsiveness across the rpm band, particularly at lower engine speeds. We’ve talked about this in other articles, but basically changing the intake runner length changes the intake air velocity, which changes how well the air flows into the cylinder.

The turbocharger isn’t anything crazy at all. It’s a variable geometry turbo supplied by Garrett. If you didn’t already know, VGTs work by using movable vanes to effectively change the size of the turbo, which has a big impact on how quickly it spools up and how much boost pressure it can produce at certain RPMs, which simply means you have the benefits of both a small and big turbo in one system.

Okay, now let’s move down to the cylinder block and the internals of the engine.

Block and Internals

As mentioned earlier in the article, the block of the LM2 is constructed from cast aluminum, for the same reason that the head is, which is weight and thermal efficiency. It’s also worth noting that because the LM2 has a different end goal as compared to larger diesel engines like the L5P Duramax, it doesn’t need an iron or CGI block. Aluminum is more than strong enough in this application because the target power levels are much lower than the bigger Duramax engines.

More specifically in regards to the weight, GM claims using aluminum for this engine saves approximately 25% of the weight over a comparable cast-iron engine block. Inside the block, GM is using iron cylinder liners for better long-term durability.

Furthermore, the block uses a deep-skirt design, which simply means the block casting extends below the crankshaft centerline, to aid in block stiffness. It’s complemented by a stiffness-enhancing aluminum lower crankcase extension attached to the main bearing caps.

Speaking of which, there are seven nodular iron main bearing caps to hold the rotating assembly in place. The rotating assembly itself consists of a forged steel crankshaft, forged steel connecting rods, and hypereutectic aluminum pistons.

The alloys in the respective castings for the rods and pistons make them lightweight and durable. At the top of the pistons, you’ll find a thick piston crown and reinforced top ring for extra support. The pistons themselves give the engine a relatively high 15:1 compression ratio.

All of this simply means the block and the internals on the LM2 are pretty decent. Next, let’s quickly take a look at the injection system.

Oiling System

The oiling system is another point on this engine that some are iffy with because it’s also rear-driven like the valvetrain is. And on top of being rear-driven, it uses a belt that has a 150,000-mile replacement interval. That means literally every 150,000 miles, you’re supposed to pull the transmission and transfer case just replace a belt. Understandably, this pisses a lot of people off.

The pump itself is a little interesting in how it works because it’s a variable pressure system and continuously changes the displacement to optimize oil pressure based on engine speed and load, which basically means it doesn’t move more oil than it really needs to.

Oil jets located in the block are used for performance and temperature control, and they simply work by spraying oil at the bottom of the pistons to help keep them cool. This allows the engine to produce more power without overwhelming the pistons because more power equals more heat. Speaking of heat, that brings us to another interesting part of the LM2 which is the Active Thermal Management system.

Active Thermal Management

The Active Thermal Management is deployed to help warm the engine quicker in cold climates, as well maintain optimal engine temperature for improved performance and emissions output. As part of this system, coolant flow is split between the head and block. This whole system works by using three valves to distribute coolant in areas where it’s most needed.

It sends heat where it’s needed to warm up the engine to reduce friction and heat the passenger cabin or cools when needed for high-power operation. Moving all the coolant around is a conventional style water pump and its the ECM that control the valves to direct coolant around the engine, and it’s based on a number of coolant temperature sensors throughout the engine, including a temp sensor for the block, the head, engine inlet, engine outlet, radiator outlet, heater core inlet and outlet, and more.

Emissions Systems

Moving on, let’s look at the worst part of any modern diesel engine, and that’s the emissions systems. Starting with the EGR, GM actually changed things up quite a bit. The LM2 utilizes a new low-pressure EGR system, where traditionally, EGR systems are high-pressure.

However, high-pressure EGR systems generally require efficiency-robbing assistance from the turbocharger or other supporting elements to achieve the pressure differential required for sufficient EGR flow rates.

The LM2’s low-pressure system adds to the high-pressure system, supporting the continual adjustment of exhaust back-pressure for more efficient operation. It recirculates gases between the low-pressure points in the exhaust system which is downstream of the DPF and after the compressor inlet.

When the low-pressure EGR is activated by an electronically controlled valve, the engine burns exhaust gas that has already passed through the particulate filter. That increases the turbocharger’s efficiency, which helps overall vehicle efficiency without deteriorating the rate of particulate matter emitted by the engine.

If you didn’t already know, the EGR system basically just diverts some of the engine exhaust gas and routes it back into the intake, which ultimately lowers combustion temperature.

It features a diesel particulate filter or DPF, which captures excessive exhaust soot and burns it off through a regeneration mode, as well as selective catalyst reduction with diesel exhaust fluid injection. It’s a little too soon to know how these emissions will fair in the long term, but looking at other examples, I’m pretty confident these systems will become reliability issues down the line.

Major Issues

In terms of major issues, it’s a little too soon to know all of them, but there definitely seems to be a no-start issue, no-crank, or long-crank issue popping up on some of these trucks, which appears to be related to the camshaft position sensor. What’s really annoying about this issue is that it’s another thing that requires the transmission to be removed in order to access.

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