As avid diesel fans, we were excited when General Motors announced the Duramax L5P, and considering how the engine has performed, I consider it exceptional. I have likely the most thorough experience, as I have driven a 2018 Silverado 2500HD, with a Duramax engine, and have driven it to 200,000 miles. Most notably, I have driven it long enough to monitor and calculate its oil consumption. I have documented an extensive report of consumption patterns, with the intent to provide useful knowledge to current and prospective L5P owners, in order to assist with their oil consumption knowledge for the L5P.
The L5P Duramax’s Technological Advancements
Most would agree that technological advancements with the L5P Duramax represent a more refined step in diesel engine technologies. It has a 6.6L Turbocharged V8 engine, with outstanding technological advancements. Among engines, it is spec’d with the most highly regarded advancements in emissions control technologies, alongside VVT, and a fuel injection system that is capable of operating over 36,000 pounds of pressure. While most engines of the L5P’s generation, for example, LML and LMM, had to engineer their motors, L5P had the good fortune of having the engineers design the package from scratch, allowing for a greater focus on meeting consumption regulations while maintaining endurance of the system.
Engine attributes such as redesigned pistons with improved cooling galleries, aluminum cylinder heads, and a completely new block casting contribute to commercial L5P Duramax engines’ thermal management in a way that positively impacts the oil consumption characteristics over the lifespan of the engine. Additionally, L5P Duramax engines hold an approximate 10 quart oil reserve, which positively impacts oil lubricated parts and service intervals.
Oil Consumption During Initial Break-In Period
Prior to reaching 10,000 miles, owners of the L5P Duramax engine begin to notice the oil consumption pattern. Concern begins to set in after an engine begins to consume oil at a quart every 3,000 miles. Discussing with mechanics and fellow owners helps to ease the concern because the oil consumption pattern is expected.
Break-in is necessary in order to ensure the pistons seal well against the cylinder walls. During break-in, oil usage should begin to decline after the initial usage as the piston rings begin to seat and less friction is experienced. Additionally, as the engine is used, particles from the manufacturing process that temporarily increase oil consumption, begin to break down and decrease oil usage.
Characteristics of Oil Usage During Mid Life Interval
Between 10,000 to 100,000 miles, the L5P Duramax engine shows remarkably consistent oil consumption. During this period, oil consumption on my engine stabilized at about 1 quart per 5,000 to 7,000 miles. This stability is indicative of the engineering and manufacturing quality that GM incorporated with this new generation of Duramax diesel.
This stability varies with driving conditions and maintenance. Highway driving is usually associated with lower consumption than constant towing or heavy payload driving. When towing my travel trailer, which weighs 12,000 pounds, I increased my consumption to about one quart per 4,000 miles. This is acceptable for a turbocharged diesel working under load.
Consumption patterns are influenced by a variety of external and internal operating conditions. When driving in cold northern climate conditions, oil consumption is likely to be higher. This is due to the engine management system enriching the fuel more and extending engine warm up times. In hot and dry summer driving conditions, oil consumption is also likely to be higher due to the thermal stress that is placed on the engine.
Trends In High-Mileage Oil Consumption
Once my odometer exceeded 150,000 miles, I was monitoring my vehicle’s oil levels, expecting increases in mileage-related oil consumption, but documented stable oil consumption for the L5P Duramax. During the interstate drives from 150,000 miles to 200,000 miles, I recorded oil consumption of roughly 1 quart for every 4,500 to 5,500 miles, again stable throughout the dry interval.
Such evidence speaks to the L5P Engine. Improvements in piston cooling, metallurgy of the critical components, oil control ring design, and tolerances allow for greater performance. Oil analysis showed wear metal levels and allowed for the monitoring of the components.
Variables Affecting Oil Consumption
Oil Quality
The quality of oil is, arguably, the most important variable affecting driver oil consumption via L5P diesel engines over their usable life. Premium synthetic diesel oil, aligned to the specific GM Dexos-2 standard, and the subsequent oil change intervals performed every 7,500 miles ought to be utilized to optimize protection and minimize consumption. In my case, consumption aligned to the anticipated trend and oil quality.
Driving Patterns
Driving mannerisms are yet another factor. Oil consumption will be worse during aggressive driving (frequent high-RPMs, rapid cold starts, and stop-and-go driving) than during steady-state highway driving. Additionally, my understanding is that the L5P Duramax turbocharger will also contribute to higher consumption, as the high temperatures and rapid turbulence within the housing can cause oil to be vaporized from the compressor seals and be drawn into the intake.
Air Filter Maintenance
In the interest of efficiency, I will not elaborate on oil consumption related to air filter maintenance. I think it can be understood that a dirty air filter causes the engine to work harder which can lead to more oil being bypassed by the piston rings due to higher cylinder pressures. I follow a regimented filter replacement schedule and replace the filter as soon as I perceive it to be even marginally more restrictive than before.
Comparison to Previous Duramax Generations
I can compare the L5P Duramax to earlier generations due to my ownership of an LML Duramax. I can say that the L5P is, on average, a lower oil consumer than the LML within the range of miles that I have driven them. The LML used to burn 1 quart of oil every 2,500 to 3,000 miles after 100,000 miles and the L5P is consuming oil at rates almost 1 quart every 5,000 miles.
The improvements can be attributed to the multiple engineering changes GM made, such as the revised piston ring package, the updated crankcase ventilation system, the better cylinder bore finishes, and the L5P improving emissions system. Lastly, the emissions system places less thermal stress on engine oil, which helps sustain its protective qualities for longer service intervals.
Optimizing Performance Beyond 200,000 Miles
Regular Oil Analysis
Hitting 200,000 miles on my L5P Duramax confirmed additional oil analysis. Regular oil analysis helps to troubleshoot deteriorating engine symptoms before they result in increased oil consumption or a loss of power. Measuring wear metals, fuel, and coolant contamination helps identify damaging trends that may go undetected.
Fuel Quality Matters
Attention must also be paid to fuel quality. Low quality diesel fuel can lead to the formation of carbon on the piston crowns and rings which can then lead to oil control issues. Top Tier diesel fuel and fuel system cleaning treatments can help preserve the efficiency of fuel combustion, and can help decrease the formation of combustion byproducts that can lead to increased fuel consumption.
Crankcase Ventilation System
The crankcase ventilation system also needs to be inspected periodically. The L5P has a closed system that re-circulates blow-by gases that can lead to crankcase pressure increases which can cause oil to be pushed past seals and gaskets. During routine maintenance, ventilation hoses and oil separators should be inspected to ensure that blockages are not leading to pressure consumption issues.
Conclusion
My 200,000-mile experience with my L5P Duramax has proven that with adequate maintenance, these engines are capable of developing excellent oil consumption patterns. It is fully understandable that with consistent use of these engines over several hundreds of thousands of miles that a better understanding of the consumption patterns would allow the users to better identify the consumption patterns and avoid potential problems that would require the attention of a professional.
Frequently Asked Questions
What is considered acceptable oil consumption?
The question many owners have is whether the oil consumption is at an acceptable level. Oil consumption is usually considered to be acceptable at the level of 1 quart every 2,000 miles. In actuality, most engines perform better than this threshold, and any engine that performs below this should be inspected by a dealer, especially if it is under warranty.
Does DPF regeneration affect oil consumption?
Another question that is often asked is whether oil consumption is going to be impacted by diesel particulate filter regeneration cycles. More specifically, during active regeneration wherein the engine injects extra diesel fuel, there is also the possibility that some of the fuel can be pushed past the piston rings and into the crankcase. Although this is a possibility, the injector positioning, spray pattern, and design of the L5P are all improvements over earlier injector designs and as a result, this means less impact on oil consumption.
Does switching oil brands impact consumption?
Do owners changing oil brands impact consumption? One of the important factors is quality; however, brand loyalty, a singular premium lubricant, allows the engine to fully ‘marry’ to its particular traits. Brand switching can impact consumption as a result of different additive packages reacting to the system’s residual oils.
Can I extend oil change intervals?
Extended oil change intervals is a question that comes up, which is similar to consumption. The L5P can withstand extended drain intervals of 10,000-mile driving conditions; however, intervals of 5,000 to 7,500 result in better consumption and improved engine longevity even in less severe operating conditions.