LB7 Duramax Engine Problems - Top 5 Most Common Issues


LB7 came into existence in 2001, which is OG 6.6L Duramax. Spanning around 20 years of manufacturing and six different variations, the LB7 has undoubtedly proved to be a durable and reliable platform. Engineers have eradicated many problems associated with the LB7 Duramax up till now. So, LB7 is a sound engine with good performance and reliability for its age.

5 Common Problems of LB7 Duramax ​Following are the five common 2015 Duramax problems related to the functioning of the LB7 Duramax engine.

  • Water Pump Failure

  • Overheating (Radiator gunk, fan clutch issues)

  • Fuel Injector Failure

  • Fuel Filter Housing O-ring Leaks

  • Blown Head Gasket



1. Water Pump Failure

Almost every best Duramax engine suffers from this problem. The LB7 Duramax problems are caused by the coolant side sealing on the Water Pump. Instead of plastic, the water pump of LB7 consists of cast iron. The water pump holds a seal at its side that controls the pressure resulting from the spinning shaft inside it. Over time, the seal becomes damaged and causes a coolant leak. This leakage prevents LB7 from pushing coolant across the cooling system effectively. All this results in fast overheating of the engine. Symptoms

  • Fast overheating

  • Noisy water pump

  • Frequent refills/ constant less cooling light

  • Radiator steaming

  • Coolant leakage from the engine



2. Overheating

Overheating is one of the most commonly occurring engine problems. Anyhow, the issue does not occur much frequently when towing lighter loads. Mostly, overheating occurs because of a faulty fan clutch. This part is responsible for giving both the heating and cooling effects to the engine. When the engine motor is cold, the fan will not spin. So, it allows the machine to heat up more rapidly. The fan kicks in when the optimal temperature is reached, thus preventing overheating. The second most vital reason for overheating the engine is the dirty radiator. Over time, the radiator naturally becomes dirty with many particulates. This debris reduces the performance of the radiator and causes overheating of the engine. The issue of overheating becomes aggravated when pulling heavy items. Moreover, the problem becomes even more common in summers due to hot surroundings.


3. Fuel Injector Failure

In LB7 engines, fuel is injected in cylinders instead of into the intake manifold. The direct injection needs the insertion of energy at very high pressure. The LB7 injectors had two potential flaws that can cause the failure. Firstly, the injector's internal ball seat used to become damaged over time, which caused leakage. Secondly, the injector itself used to be prone to cracking. Both of these issues of injector caused problems because air to fuel ratio was not in order anymore. Mostly, injector issues used to result from flawed design. Symptoms

  • Rough idling

  • Engine misfires

  • Rich bank codes or CLE's for lean

  • An overall decline in performance

Now, newly designed injectors are introduced, which come with seven years warranty which means a mileage of about 200,000. Now, most of the vehicles have these upgraded injectors in their engine. However, even the upgraded injectors are also prone to failure. Also, replacing these new injectors is an arduous task. Alongside the cost, labor needs 16 hours as they have to sit under rocker cover. Also, they need to remove many parts to reach the injectors.


4. Fuel filter housing

​Fuel filter filters the fuel before it moves through lines to injectors. On the LB7 Duramax, fuel lines mostly undergo leakage. However, filter housing causes the majority of the leaks in LB7 fuel. The head of the housing uses many o-rings to block the pump. Gradually, these o-rings decline due to natural damage. Thus, they cause leaking of the fuel. These fuel leaks affect fuel supply towards the engine. Also, the air gets into the fuel lines through these leaks. Thus, this air will cause various performance issues. Symptoms

  • Performance issues, shaky idling, engine misfires

  • Low fuel engine codes

  • Fuel pump drops prime making it hard to start the engine

You have two replacement options. Firstly, you can purchase a new head assembly. Secondly, you can go for a rebuild kit and change the gaskets, bolts, and o-rings, etc. Both options are cost-effective. So, it would help if you preferably went for the whole assembly for the greater good.


5. Blown Head Gasket

Head gaskets are among the most common failure spots on LB7 Duramax for various reasons. These engines are known to overheat when towing typically. Sometimes, excessive heat creates this issue. Moreover, LB7 engines with higher horsepower are more prone to this problem as well. For the majority of head gasket blows, the design of the gasket is the reason. Over time, the gasket naturally declines. It ultimately causes a leak; when the leaks are outwards, coolant leaks on the block's outer side. If internal, coolant leaks into the cylinders. In fine, LBS7 is a good contender for primitive diesel engines. If you are looking for a budget-friendly diesel engine option, go for it. Problems are associated with every motor out there; you need to understand and resolve them timely.

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