The Duramax diesel engine family evolved from the first generation in 2001 to today. Each generation brought up some improvements both in construction and performance. When the LMM engine was developed, it was hit with massive emission restrictions. That demanded adaptations and asked whether the LMM Duramax was a good engine.
So, is the LMM Duramax a good engine? It came after the LBZ, which was the favorite in the market. With new emission standards, GM needed to adapt. The LMM has a DPF and a smaller turbocharger. The LMM is remembered as an engine with many problems connected to the new emission control systems. Still, it is a good engine that stepped in when the times were hard.
Despite the focus on emissions, the LMM had other improvements. It has a revised head design and a new intake airflow valve. That allowed better airflow, keeping the engine robust despite the emission regulations. The production lasted between mid-2007 and 2010 when it was replaced with the LML Duramax.
Overview of LMM Duramax Engine
The LMM has a great base in the LBZ Duramax engine. The LMM responded to the new EPA mandates that severely limited engine emissions. The biggest difference between those engines is the larger EGR and the introduction of the DPF.
The DPF was an answer to the high emission of particles from diesel engines. The DPF system trapped all the soot and particles that would end up in the atmosphere earlier. That would cause the DPF to clog relatively fast, so the regeneration process was introduced.
When the time for the DPF regeneration comes, the driver needs to drive in the highway conditions for a certain time interval. The fuel injectors would again open on the exhaust stroke and allow fuel to enter the exhaust system. The DPF then heats up while burning fuel, burning all the soot already on it.
The injectors also received an upgrade. Earlier, Duramax engines had injectors with 7 holes for fuel, while the LMM injector has 6 holes. The injectors sprayed fuel directly on top of the piston, producing a more efficient fuel-burning process. We already covered the topic of LMM injectors in another article that you can check out. If you want to change fuel injectors yourself, check the article linked.
The transmission limitations were addressed. The reliable 6-Speed Allison transmission is improved and can handle more tuning. It is also more robust and sturdy. The LMM is the first Duramax engine model that doesn’t have an option for manual transmission.
The fuel system remained the same. The high-pressure fuel CP3 pump is still used. The lack of the fuel lift pump still causes the fuel pump to overwork if the engine is tuned up.
Strict emission regulations made an impact on the old turbocharger. The LBZ has a smaller turbo, but the LMM turbo is even smaller. The engine still had 5 hp and 10 torque, more than the previous engine. The result is 365 horsepower and 660ft/lb of torque. The introduction of DPF also worsened fuel economy and lowered fuel mileage.
Specs of An LMM Duramax Engine
The LMM follows a similar design to older Duramax engines. It is a powerful and versatile engine that can have different purposes and uses. At the same time, it is reliable and can withstand a lot of tuning.
| Engine Design | 90 Degree V8 |
| Displacement | 6.6L (403ci) |
| Engine block | Cast iron with deep skirt |
| Pistons | Cast aluminum |
| Rods | Forged steel |
| Engine power | 365 hp |
| Torque | 660 lb/ft |
| Valvetrain | OHV, 4 valves per cylinder |
| Turbocharger | Garrett GT3788VA |
| Injection pump | Bosch CP3 |
| Firing order | 1 – 2 – 7 – 8 – 4 – 5 – 6 – 3 |
| Bore | 4.06 inches |
| Stroke | 3.9 inches |
| Engine mass | 835 pounds |
Is A LMM Duramax Reliable?
Yes, it is. The biggest issue is with the DPF system, which can cost you a few thousand dollars. After you hit the 150,000 miles mark, you can expect problems with the water pump, pistons, and injectors. The turbo also sometimes can cause problems.
With these things in check and with regular maintenance, you can easily go over 400,000 miles with this engine. The most important thing is to change the oil and filters regularly. Also, thanks to the DPF, some unburnt fuel goes through the engine. That fuel may cause a lack of lubrication of the cylinder walls. That can lead to fuel mixing with oil, so keep an eye on a dipstick.
Check Out The LMM Duramax – Reliability & 5 Common Problems:
What Are The Common LMM Duramax Problems
Besides the DPF issues, the rest of the problems are inherited from the older Duramax engines. Most of the problems are not engine issues. Most frequently, the problems are with pressure fuel lines and low fuel pressure.
Crankshaft Failure
If you are not planning to tune up the engine, you will probably avoid problems with the crankshaft. You can freely tune up the engine up to 500 hp if you want more than that; you should think about the stock crankshaft and its limitations.
Piston Failure
The LMM has a 6-hole injector. Two out of those 6 holes spray the fuel directly above the wrist pin on the piston. That creates excess heat in this area. That excess heat can eventually cause a crack in the wrist pin.
Like with crankshaft, this problem usually doesn’t occur on stock engine values. If you modify and tune the engine heavily, consult the tuning professionals about this issue.
Low Pressure of Fuel Rail
Problems with low fuel rail pressure are not that common. In most cases, they happen if the truck is used for heavy towing, especially in the summer. In those situations, the engine needs better fuel flow which puts pressure on the whole fuel system. Also, tuned engines require more fuel, which the fuel system cannot get.
This can cause extensive problems with the fuel pump and the fuel injectors. The CP3 pump cannot get enough fuel from the fuel tank, and the lack of the lift pump is apparent.
Some of the symptoms are reduced engine power, the P0087 error code, and problems with shifting. In this case, you need to inspect the fuel system. Sometimes the problem can be a bad pump, clogged fuel filter, or transmission line leaks.
The best thing to do is to install a lift pump. That way, you will put away some pressure from the CP3 pump. Also, you can upgrade the fuel lines. These are harder to install, but you will not have to change them so often.
All Duramax engines will run better with better diesel fuel and with the help of a fuel additive. With those, you will minimize the problems with the fuel system.
Transmission Lines That Leaks
The fuel transmission lines have a design flaw that causes them to leak. This especially happens in cold weather or when the engine is cold. If you notice a puddle of red transmission fluid under the truck, that is a sure sign of a leak. Also, hard shifting and high transmission temperatures happen when there is insufficient transmission fluid.
If you notice any of these issues, address them immediately. Keep an eye on levels of transmission fluid. This problem is frequent; most truck owners must change the transmission lines every 30,000 to 40,000 miles.
What Vehicles Have LMM Duramax Engines?
The following vehicles used this powerful 6.6L V-8 engine:
- Chevrolet Silverado HD
- Chevrolet Express
- Chevrolet Kodiak
- GMC Savana
- GMC Topkick
- GMC Sierra HD.
Is An LMM Duramax Engine Worth It?
An LMM engine is a powerful and reliable engine model. It offers great stock power and torque. Trucks with this engine are great for different roles but with some minor glitches. Pay attention to the DPF and fuel system; you should be fine.
Another great thing about this engine is the amount of power it can produce when tuned up. You can easily double up its power. Just leave this job to professionals. Some of the stock parts have a limit of around 500-550 horsepower. You can replace them and get even better results.
FAQs
What year is the best LMM Duramax?
There are no better or worse engine year models for this engine. You can pick either year. What is essential is to check the overall state of the engine. You should check how well the engine is maintained and the purpose of the vehicle. Truck owners can use the truck for towing, drag racing, or for some specific function. Those can shorten the work life of an engine.
What transmission does an LMM Duramax have?
LMM Duramax uses the Allison 1000 6-speed automatic transmission. Duramax engines before the LMM had an option of a manual ZF6 transmission, but it is phased out at LMM.
How much is the HP of a 2008 LMM Duramax?
All LMM engines have 365 stock horsepower. They have a great horsepower output and even better horsepower capacity when tuning.
What Is The Life Expectancy of An LMM Duramax?
All Duramax engines are known for their long work life and sturdy design. They can go well over 300,000 miles with little more than regular maintenance. If you decide to keep the engine for a long time, you can expect it to go over 500,000 miles.
Final Considerations
You cannot find a bad engine when you look at the Duramax engine line-up. With each generation, they brought something new. The LMM introduced systems for fuel emission reduction. A drop usually follows that in power. In the case of the LMM, it also has some added power.
Some of the problems from the older Duramax engines remained, but it is a great engine. With proper regular maintenance, you can expect it to last more than 300,000 miles. You can also tune it and get a monster engine and a truck that can do almost anything. For further mechanic advice, stay with us!
