GM 6.6L Duramax L5P Engine Specs, Problems, Reliability, Info

6.6L Duramax Diesel Engine Info

The 6.6L Duramax L5P Diesel is a 6.6-liter V8 turbocharged diesel engine manufactured by General Motors for use in full-size heavy-duty (HD) pickup trucks, such as the Chevrolet Silverado HD and GMC Sierra HD. The GM L5P engine is the latest generation of the 6.6-liter Duramax V-8 lineup, which debuted in 2017 model year, replacing the LML version. The new 6.6L successor is the most powerful GM diesel engine ever made, with an output rated at 445 horsepower (332 kW) and 910 lb-ft (1,234 Nm) of torque. This next-generation motor has a lot of new and improved components and systems compared to the previous version. So, let's take a closer look at how it was built, what has been changed, learn about its specs, pros and cons.

6.6 Duramax L5P V8 Diesel Engine Design Features

The L5P got a new cylinder block made of high-strength heat-treated cast iron, featuring induction-hardened cylinders to reduce wear. It shares the size of the bore and stroke with its predecessors. The L5P block features an increased number of mounting points and ports in the valley of the block, additional two M8 cylinder-head bolts at the upper corners, the 0.1693-inch (4.3 mm) increase in deck height and a 20 percent increase in strength. This block is also 9 pounds heavier. The new block comes with eight oil squirters that are able to supply up to 1 gallon of oil per minute to each piston.

Pistons and connecting rods have been completely redesigned. Pistons are made of aluminum, and they feature increased to 2.1377 inches (54.3 mm) compression height and a larger 1.4173 inches (36 mm) wristpin diameter. The connecting rods are powder-cast and they comes with offset bearing caps. The new engine is equipped with a more productive oiling system. The L5P gear-driven oil pump features 19.6% greater capacity than its predecessor, providing 21 gallons per minute. Being an OHV pushrod engine, the L5P has a single gear-driven camshaft located inside the block in a valley between cylinders. This engine utilizes LS-based mechanical roller lifters (138 grams) and LS-style pushrods with stronger, thicker-walled tubing. The visible difference between the new and old camshafts is the width of the lobes - the L5P's lobes are narrower. It also features a new camshaft profile.

On top of the block, there are redesigned aluminum cylinder heads with four valves per cylinder. L5P heads have larger exhaust ports and reshaped intake runners for improved airflow and volume. Valve sizes remain the same. The L5P Duramax is equipped with Denso G4S Gen III solenoid-type injectors and the Denso HP4 high-pressure fuel pump, instead of Bosch fueling components. The HP pump is now fed by an in-tank supply pump that maintains a pressure of 4 bars. On the exhaust side, there are cast nodular iron exhaust manifolds with steel pipe extensions leading to a new Borg Warner electronically controlled, variable-vane turbocharger with a billet compressor wheel. The new 6.6L Duramax engine produces more power with less exhaust emissions thanks to not only a variable-vane turbocharger and precise fuel delivery, but also advanced emission control systems, including Cooled Exhaust Gas Recirculation (EGR), Diesel Particulate Filter (DPF) and Selective Catalytic Reduction (SCR). It also runs on ultra-low-sulfur diesel and B20 biodiesel.

The 2017 model year L5P Duramax is rated at 445 horsepower (332 kW) at 2,800 rpm and 910 lb-ft (1,234 Nm) of torque at 1,600 rpm. General Motors also produced a detuned version of the L5P - the L5D Duramax. This version was used in Chevrolet MD trucks (Silverado 4500HD, Silverado 5500HD and Silverado 6500HD) and International CV trucks. The power output of the L5D engine is 350 hp (261 kW) at 2,600 rpm and 700 lb-ft (949 Nm) at 1,600 rpm. The second-generation L5P was introduced for the 2024 model year, featuring an updated turbo design and even more power and torque: 470 hp (350 kW) at 2,800 rpm and 975 lb-ft (1,322 Nm) at 1,600 rpm.

Engine Specs

Chevrolet GMC 6.6L Duramax Problems and Reliability

The L5P Duramax engine relies on precise injector timing, electronics, emission hardware (DPF, SCR catalyst and DEF injection system). If any of these components fail, they can take the truck down with them. Fortunately, the L5P engine is widely regarded as a robust and reliable diesel engine with only a few common problems, including excessive regeneration frequency, DEF system failures, diesel particulate filter clogging, and Common Rail injection system issues.

Fuel System Problems

The L5P has a modern high-pressure common rail fuel system that relies on clean diesel without water contamination and clean filters. Even a small amount of dirt, carbon, or metal shavings from the high pressure pump and internal deposits can clog and damage expensive fuel injectors, causing rough idling, poor fuel economy, and stalling while driving. A faulty fuel injector can significantly damage emission hardware and other engine components.

DPF Clogging

Low-quality diesel fuel, fueling system issues, or even short city trips can cause problems with the diesel particulate filter (DPF). In most cases, it simply gets clogged up, leading to potentially costly repairs. The DPF can’t be cleaned, and the only fixes are replacement or deletion.

Excessive Regeneration Frequency

The first sign of DPF failure is that the L5P initiates active regeneration cycles more and more frequently (every 50-100 miles instead of every 400-700 miles). The problem can also be caused by driving a vehicle for a long time over short distances in city environments or the use of poor-quality diesel. In this way, the L5P Duramax engine needs to burn soot more frequently. In order to reduce the number of regeneration cycles and potential issues with the DPF in the future, it is recommended to take weekly highway trips, reduce idle time and never turn off the engine until the cycle is complete.

DEF System Failures

The DEF tank heater, pump, and injector are the main sources of DEF system failure. Any faulty DEF component triggers the limp mode (a 55 mph speed limiter). By the way, the limp mode can also be triggered by a faulty exhaust gas recirculation (EGR) system.

6.6L Duramax L5P Engine Longevity

Like any modern diesel, the L5P Duramax engine experiences regular wear and must be properly cared for to extend its lifespan. This 6.6-liter V8 diesel engine is capable of exceeding 350,000 miles (550,000 km) with regular maintenance and high-quality fuel and oil.