Duramax Years to Avoid When Buying

Since 2001 till date, GM has produced about 11 types of Duramax engines.

Compared to current models, its earlier models have some issues.

In specific Duramax 2001-2010 model year should be avoided.

Let’s discuss in detail why you should avoid these model years

Duramax Years to Avoid

You should avoid buying Duramax LB7, LLY, LBZ, and LMM.

In short, you must avoid buying Duramax 2001 to 2010 model year.

On the other hand, Duramax L5P is the best Duramax to buy.

If you don’t have enough budget to buy L5P then you can go for Duramax LML.

Duramax is a great engine, but some of its earlier versions have issues that later versions overcome.

For better fuel economy, power, reliability, and comfort, the newer models are better than their older ones.

If you are looking for a Duramax engine in the market, you must know which years should be avoided.

Avoid these 4 models of Duramax.

  • Duramax LB7 [2001 to 2004]
  • Duramax LLY [2004 to 2005]
  • Duramax LBZ [2006 to 2007]
  • Duramax LMM [2007 to 2012]

All engines can have minor issues, but some engine problems can outweigh their benefits.

The models mentioned in the above list are one of them.

Let’s learn why should you avoid these models.

01. 2001-2004 Duramax LB7

lb7 duramax years to avoid

LB7 is the first engine of Duramax, which is 6.6L.

The engine will provide 230 to 320 HP and about 480 to 520 lb/ft of torque.

It came with 2001-2004 Chevrolet Silverado, Chevrolet Kodiak, GMC Sierra HD, etc.

The engine was recognized as the simplest model of its time because it did not carry DPF (Diesel Particular filter) and EGR (Exhaust Gas Recirculation) system.

The systems were added later.

The common problems of LB7 are-

Water Pump Problem

The earlier LB7 water pump was made of cast iron.

There was a seal on the side of the coolant in the water pump.

The seal was defected from a normal tear or wear and became the major reason for coolant leaking.

It will affect the cooling system of the engine and cause engine overheating.

Then GM changed it to plastic on the 2006 model to solve problems.

Injector Issues

The LB7 engine’s original injector came with common problems like cracking.

The symptoms of injectors issues are excessive smoke at idling, hard start, or fuel in the oil.

Replacing the injector is the best way to solve the problem if it is original.

GM resolve it in the later version, so I recommend checking papers properly before buying an injector.

Head Gaskets Problems

After LB7 reaches 100k to 150k, head gasket problems are commonly shown.

GM used a multilayer steel head gasket which is mainly blamed for the gasket problem.

Because of its poor design, the head gaskets sometimes fail and cause coolant and oil to mix, leading to engine damage.


While towing, the overheating problem with LB7 is commonly reported.

The foul water pump is responsible for overheating in LB7.

The problem with the engine fan is also a reason for the heating and cooling effects on LB7.

If the radiator of LB7 is dirty, it will be another reason for overheating.

Since overheating problems can occur for several reasons, it’s best to take the vehicle to a qualified mechanic for troubleshooting.

LB7 Fuel Filter Housing O-Ring Leaks

If the O-ring is not seated correctly in the housing or if the O-ring is damaged, it allows fuel to leak past it into the engine.

O-ring leaks also lead air to enter the fuel system of the engine.

It is a common problem with the LB7 engine.

02. 2004-2005 Duramax LLY

worst duramax years

The LLY Duramax engine was first introduced in 2004.

The engine will provide up to 300 HP and about 500 to 600 lb/ft of torque.

This turbocharged (32-valve) diesel engine came with GMC Sierra and Chevy Silverado.

This year of LLY contains some of the problems, which are-

Engine overheating

The Duramax LLY faces overheating problems like LB7 because of its insufficient cooling system.

The engine overheating problem occurs because of its small radiator and cooling fans.

The problem occurs when towing a heavy load or driving at a hot temperature.

The updated version of this model resolves the issues.

Head Gaskets Problems

LLY carries the same head gasket problem as like LB7.

This issue is caused by LLY’s large turbocharger and the size of the inlet manifold.

The small size of the inlet manifold decreases the turbocharger’s performance and causes overheating engine.

Overheating and pressure deteriorate the head gasket.

Glow Plug Failure

The LLY engine is prone to glow plug failure.

The glow plug of LLY fails if its module is faulty.

Sometimes, the glow plugs can become corroded and fail.

Injector Harness Chafing

As LLY was an older engine, injector harness chafing problems are commonly reported.

Including the described problems, the LLY engine has other problems like water pump issues, EGR valve, lift pump issues, etc.

03. 2006-2007 Duramax LBZ

worst duramax engine

LBZ is a famous engine.

It is popular and has overcome many problems with its competitors.

The engine will provide around 365 HP and 655 lb/ft of torque.

It is also a reliable engine, but a few key issues make its position on our list.

Except for this problem, overall, Duramax LBZ is a good engine.

The issues are-

Cracked Piston

This problem was reported by some users, that their Duramax 6.6L LBZ engine piston cracked after reaching 90k miles.

The problem occurs because of the size of the LBZ engine piston.

This will be a problem for someone who wants to add a mod on their LBZ engine; however, it’s not a problem for those who want to stock it.

Glow Plugs Problem

LBZ didn’t overcome this problem like its older version.

A device that is used for heating and starting a diesel engine in cold weather is called glow plugs.

If LBZ engine glow plugs are damaged, starting the engine at a low temperature is difficult.

It is an extremely important device in a cold country.

Water Pumps Issues

Many reports have come that the 2006-2007 Duramax LBZ engine failed to push the coolant properly into the engine coolant system.

It is one of the major reasons for an engine.

Weak Plastic Impeller

An impeller is a rotating component that use to rotate the coolant.

LBZ engine impeller is made of plastic material which is weak and easily breaks or damaged.

04. 2007-2012 Duramax LMM

The Duramax LMM replaced the LBZ in 2007, but if calculated mechanically, there is a minimal difference between LBZ and LMM.

The LMM has an emission control system, which is absent in LBZ.

The engine will provide 360 to 370 HP and around 665 lb/ft of torque.

This engine comes with Chevrolet Silverado HD, Chevrolet Express, GMC Savanna, GMC Sierra, and other related models.

This engine has some problems which should be noticed.

DPF Issue

LMM has a DPF system which used to take and remove diesel particulates.

The diesel fuel burning produces these particulates.

A regeneration cycle usually occurs in DPF every 670 to 700 miles or when the DPF collects around 44g of soot.

And the DPF issues on the Duramax LMM are caused by a build-up of soot in the filter.

This can happen if the truck is not driven enough or if it is not driven hard enough.

When the filter gets full, it can cause the engine to lose power and eventually stall.

Crankshaft and Piston Issues

As I mentioned, LMM is a reliable engine, but it has a few issues, such as the piston or crankshaft cracked in high hp.

There is no record of piston or crankshaft failure in a stock LMM engine so you can drive with the stock engine without any worry.

But if someone intends to modify LMM for high performance, it causes piston or crankshaft cracking.

Statistics say it is 600whp when the LMM piston and crankshaft fail.

Allison 1000 Power Limitations

Any extra power will affect your transmission, whether a heavily modified engine or a modest tune.

Driving a modest tune with exhaust & intake will not cause any problems, but if you add an extra 100 to 150hp, it will cause a weak Allison issue.

This same type of problem is also found in the LBZ engine.

A transmission control module (TCM) will help reduce the problem.

The Allison will handle 450whp with a TCM tune, but 500whp will exceed the endurance limit.

In some cases, leaking transmission lines and fuel rail pressure problem is also seen in LMM engine.

Duramax Best Year to Select

Firstly Duramax L5P and secondly LML are the two best Duramax to select.

If you don’t have enough budget then you can also go for-

  • Duramax LGH [2010-2017]
  • Duramax XLD28 [2012-2021]
  • Duramax L5P [2017-2021]
  • Duramax XLD25 [2011-2021]
  • Duramax LWN [2014-2021]
  • Duramax LM2 [2019-2021]
  • Duramax LML [2011-2016]

Final Thoughts

All engines have some issues, but some major issues put an engine on the avoid list.

Duramax’s models from 2001-2010 (LB7, LLY, LBZ, and LMM) have some major problems, so they are listed in the avoid list.

Apart from these, the new models are functional and useful, which are listed above.

Overall, Duramax is famous for its performance in the USA.

You can trust it.

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