General Motors (GM) has a long history of producing diesel pickups. The first GM diesel pickup was introduced in 1978 with an Oldsmobile-built diesel V8 engine. However, this engine was plagued with reliability issues and was discontinued in 1985. A 6.2 diesel was then put in the pickups which was more reliable.
In 1992 GM had a gap in their lineup of diesel pickups. So they introduced the 6.5 diesel, an updated version of the 6.2 diesel that had been around since 1982. The 6.5 was a trailblazer, being the first diesel engine in a pickup truck to feature electronic fuel injection, although it used indirect rather than direct injection. It came in two trims: naturally aspirated and turbocharged. The former produced 155hp and 340 lb.ft of torque, while the latter boasted 215hp and 440 lb.ft of torque. The 6.5, when paired with the proper gear ratio, could achieve an impressive 21 MPG while still offering enough torque to compete head-to-head with the Cummins engines of the era.
Though the 6.5 wasn't known for its performance potential, it was a reliable engine. However, there was one notorious issue with the engine: the Pump Mounted Driver, or PMD. The PMD controlled the injection pump and was the most common source of trouble with the 6.5. Despite the PMD issue, the 6.5 was still a dependable engine, and it remained in production until 2000.
It wasn't until 2001 that GM re-entered the diesel pickup market with their own engine which was a joint venture between Duramax and Izuzu.
The first Duramax engine was the LB7, which was produced from 2001 to 2004. It was a 6.6-liter V8 engine that produced 235 horsepower and 500 pound-feet of torque. The LB7 was known for its reliability and fuel efficiency, but it did have some issues with fuel injectors and overheating. Head gaskets failing was a common issue as well.
In 2004, GM introduced the LLY Duramax engine, which was an updated version of the LB7. It produced 310 horsepower and 605 pound-feet of torque. The LLY engine was known for its improved emissions and reliability, but it still had issues with head gaskets leaking from head bolts stretching.
In 2006, GM introduced the LBZ Duramax engine, which was an updated version of the LLY. It produced 360 horsepower and 650 pound-feet of torque. The LBZ engine was known for its improved emissions, reliability, and power. However, it still had issues with head gasket failure. The LBZ is one of the most reliable platforms of all the Duramax generations though.
In 2007, GM introduced the LMM Duramax engine, which was an updated version of the LBZ. It produced 365 horsepower and 660 pound-feet of torque. The LMM engine was known for its improved emissions and reliability, but it still had issues head gaskets. The DPF system was also a major headache for owners once the trucks reached around 150,000 miles.
In 2011, GM introduced the LML Duramax engine, which was an updated version of the LMM. It produced 397 horsepower and 765 pound-feet of torque. The LML engine was known for its improved emissions, reliability, and power. It also introduced a new emissions system known as selective catalytic reduction (SCR).
In 2017, GM introduced the L5P Duramax engine, which is the most powerful Duramax engine to date. It produces 445 horsepower and 910 pound-feet of torque. The L5P engine was a complete redesign from the previous generations, with improvements in both reliability and performance. Notable changes include moving the turbo closer to the center of the engine, switching suppliers to Denso for the injection pump (HP4) and injectors, and equipping the L5P with a lift pump. Additionally, the L5P has a high tuning potential, it is possible to safely extract 550rwhp with tuning only.
While previous generations of Duramax engines had issues with fuel injectors, overheating, head gaskets, and reliability, the L5P Duramax engine is relatively new and has not had any major issues. The L5P is a well-engineered engine that is powerful and reliable, with a high tuning potential. It is a testament to GM's dedication to improving its diesel pickups and staying competitive in the market.