The Duramax is a series of diesel engines created through a joint venture between General Motors and Isuzu, primarily for use in GM’s heavy-duty trucks. The Duramax was developed to replace GM’s underpowered 6.5L diesel and better compete with the diesel engines offered by Ford and Ram. The history of the Duramax engine is categorized by its generational changes, each denoted by a unique Regular Production Option (RPO) code. Duramax history by generationLB7 (2001–2004)

• Significance: The original 6.6L V8 Duramax brought modern diesel technology to GM trucks, including high-pressure common-rail direct injection. This led to a significant and immediate increase in GM’s market share for heavy-duty pickups.
• Initial Power: 300 horsepower and 520 lb-ft of torque.
• Key Issues: Injector failures were a notable and costly issue in this first generation. 

LLY (2004.5–2005)

• Advancements: This generation introduced an Exhaust Gas Recirculation (EGR) system for emissions control and was the first to use a variable-geometry turbocharger.
• Power: Increased slightly to 310 horsepower and 605 lb-ft of torque.
• Noteworthy Issues: This model is known to have some overheating issues. 

LBZ (2006–2007)

• Reputation: The LBZ is often regarded as one of the most reliable and sought-after Duramax engines by enthusiasts.
• Power: Boosted to 360 horsepower and 650 lb-ft of torque.
• Distinction: It was the last generation to avoid complex emissions systems like the Diesel Particulate Filter (DPF), which contributed to its reputation for simplicity and durability. 

LMM (2007.5–2010)

• Emissions Technology: In response to stricter regulations, the LMM was the first Duramax equipped with a Diesel Particulate Filter (DPF). This system, while reducing emissions, was prone to issues and decreased fuel economy.
• Power: Ratings were 365 horsepower and 660 lb-ft of torque. 

LML (2011–2016)

• Emissions Refinement: The LML improved upon its emissions system by adding Selective Catalytic Reduction (SCR) and a Diesel Exhaust Fluid (DEF) system to help with DPF regeneration.
• Power: Increased significantly to 397 horsepower and 765 lb-ft of torque.
• Key Issue: A major weakness of the LML was the Bosch CP4 fuel injection pump, which was notoriously prone to catastrophic failure. 

L5P (2017–present)

• Performance: A complete redesign made the L5P the most powerful Duramax ever, with output now reaching as high as 470 horsepower and 975 lb-ft of torque.
• Reliability Improvements: Addressing past failures, the L5P switched fuel system suppliers to Denso and added a factory-installed lift pump, significantly improving reliability. 

Other notable Duramax engines

• 3.0L Duramax (LM2, LZ0): This inline-six turbocharged diesel engine was introduced for light-duty trucks like the Silverado 1500 and Sierra 1500 in 2019. It provides a balance of power and impressive fuel economy.
• Medium-Duty Diesels (LGH, L5D): Duramax also powers medium-duty commercial vehicles, vans, and SUVs with engines like the LGH and L5D. 

When dealing with diesel engines and diesel systems overall, proper and timely maintenance is the key to keeping your truck running well for the long haul. Over the decades, the driving public at large has been sold on the “put gas in it and go” mentality to prove the reliability of our daily drivers. However, diesel pickups have crossed into the realm of heavy machinery we depend on to do heavy jobs. Therefore, today’s diesel engines need maintenance akin to that of heavy machinery. We, as diesel drivers, cannot afford to just “gas and go”.

One area in particular that deserves close attention is the DPF system. This system has the unfortunate reputation for being unreliable, problematic and downright failure-prone. The fact is, like all things diesel, treating your DPF system with care is crucial for its reliability and longevity.

The majority of problems associated with DPFs is due to the clogging of soot particles in the filter. DPFs need to burn hot and long in order to “regenerate” or clear the soot particles from the filter.

Factors that can cause the filter to clog are:

• Only driving short distances
• Excessive idling
• Low quality engine oil
• Low quality fuel
• Faulty sensors
• Failure of other components in the overall DPF system

Problems that arise as a result of a clogged DPF filter are:

• Increased fuel consumption
• Lower performance
• Limp mode
• Engine damage
• Complete DPF failure

To properly maintain your DPF:

• Regular highway driving to allow the DPF to automatically regenerate
• Only use engine oil specifically designed for DPF equipped engines
• Use high quality fuel plus a lubricant additive to protect your fuel system
• Yearly manual cleaning of your DPF at your diesel mechanic’s shop
• Promptly addressing any other problems affecting your engine as a whole
• Proactively address any DPF warning lights

DPF systems get a bad rep from the diesel community, understandably, but they are a reality we must live with. If we ignore our DPFs, then we are subject to consequences that are dolled out by the thousands of dollars. A little expense in the form of proper maintenance is all we need to make our diesel realities a little brighter.

One of the most feared powertrain failures in the modern diesel world is the CP4 high pressure fuel pump. CP4 pump failure can contaminate the entire high pressure fuel system with metal particles, destroying the fuel system as a whole. With repairs that can cost in the 5-digit range, saying that CP4 failure stings is an understatement. Fortunately, CP4 failure is easily preventable. While you cannot turn back the clock on an improperly maintained fuel pump, you can prolong the demise of a previously abused unit.

CP4 pumps can fail for a handful of reasons including air and/or water in the fuel. However, the most common reason for failure is insufficient lubrication. Lack of lube causes metal parts to wear down, not only in the pump, but in all metal-to-metal surfaces within the fuel system. Metal wear causes metal particles to contaminate the entire fuel system, thus causing more wear and more contamination. The result is a cascade of failures throughout the high pressure fuel system including the CP4 pump itself, fuel rails, fuel injectors, cam, etc. This chain reaction of failures necessitates the replacement of the entire fuel system. Step 1: remove the cab from the frame…and so it begins.

The cause of the insufficient lubrication is the fuel we use, or are required to use, in the U.S. Common domestic diesel fuel is rated as Ultra Low Sulfur Diesel (ULSD). Just as the rating suggests with no ambiguity, our diesel fuel lacks sulfur which is essential for lubrication CP4 fuel pumps. Of course, the low sulfur content was mandated to reduce emissions, but not because the sulfur is the targeted pollutant, per se. High sulfur content fuels damage the DPF systems on modern diesel engines, thus reducing their effectiveness at reducing pollutants. 

Looking at the array of additives available for diesel engines, it is hard to discern which you should use and which is just snake oil. In this case, diesel fuel lubricant is definitely something you should use. Don’t fear, these lubricant additives are not just sulfur in a bottle waiting for a chance to destroy your DPF. The engineers were one step ahead of us on this one. However, just because an additive says it is low/no sulfur doesn’t mean it is free of other ingredients that can harm your DPF. Always check the bottle of any fuel lubricant to ensure it is labeled DPF-compatible. Follow the instructions on the bottle for best results, as always.

CP4 failure can be the ultimate boogeyman for modern diesel owners, but we do not have to lose sleep over it unless we choose to. Proper fuel pump maintenance from a bottle found at your local parts store is all we need to escape the CP4 failure nightmare.

The Ford Power Stroke diesel engine is a family of engines developed for Ford’s heavy-duty pickup trucks and commercial vehicles starting in the mid-1990s. It has gone through several major generations, each with its own strengths, weaknesses, and technical advancements. Here’s a detailed history:

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Origins (Pre-Power Stroke Era)

• Before the Power Stroke name, Ford used the International Harvester (later Navistar) 6.9L and 7.3L IDI (indirect injection) diesels in the 1980s and early 1990s.
• These engines were reliable but lower in power compared to competitors, leading Ford to adopt a more modern direct-injection design.

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1994.5–2003: 7.3L Power Stroke

• Introduced mid-1994 for the ’95 model year as Ford’s first engine branded “Power Stroke.”
• Built by Navistar International.
• Key features:
  • 7.3L displacement, V8, direct injection.
  • HEUI (Hydraulic-Electronic Unit Injection) fuel system developed with Caterpillar.
  • Early versions made 210 hp / 425 lb-ft; later versions reached 275 hp / 525 lb-ft.
• Reputation: Extremely durable and reliable—often considered the gold standard of Ford diesels. Known for longevity, with many engines surpassing 400k+ miles.
• Phase-out: Tightening emissions standards forced Ford to replace it after the 2003 model year.

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2003–2007: 6.0L Power Stroke

• Also supplied by Navistar International.
• Key features:
  • 325 hp / 560–570 lb-ft torque.
  • Variable-geometry turbocharger (VGT) for better spool and drivability.
  • EGR (Exhaust Gas Recirculation) system to meet stricter emissions.
• Reputation: Infamous for reliability issues (EGR coolers, head gaskets, oil coolers, FICM failures). Ford and Navistar’s relationship soured over warranty disputes.
• Despite problems, it offered good power and aftermarket potential.

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2008–2010: 6.4L Power Stroke

• Last engine developed with Navistar.
• Key features:
  • 350 hp / 650 lb-ft torque.
  • Common-rail fuel injection with Siemens injectors.
  • Sequential twin turbos (small high-pressure turbo + larger low-pressure turbo).
  • First Power Stroke to use a diesel particulate filter (DPF) for emissions.
• Reputation: Better performance than the 6.0L but plagued by fuel economy issues, DPF clogging, cracked pistons, and fuel dilution from regeneration cycles.

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2011–2014: 6.7L “Scorpion” Power Stroke (First In-House Ford Diesel)

• Ford ended its partnership with Navistar and developed its own diesel, built in-house at the Kentucky Truck Plant.
• Key features:
  • 6.7L displacement, compacted graphite iron block, aluminum heads.
  • Unique reverse-flow heads (exhaust exits through the valley, turbos mounted in “hot-V” configuration).
  • Single sequential turbo with dual compressor wheels (later changed to a single Garrett GT37).
  • 390 hp / 735 lb-ft torque at launch, later bumped to 400 hp / 800 lb-ft.
• Reputation: Much more reliable than the 6.0/6.4, strong aftermarket support, and better fuel efficiency.

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2015–2019: Refined 6.7L Power Stroke

• Updated turbo and fuel system improved reliability.
• Power and torque steadily increased:
  • 2015: 440 hp / 860 lb-ft.
  • 2017 (with new Super Duty body): 450 hp / 935 lb-ft.
• Reputation: A dependable and powerful diesel, often seen as Ford’s redemption in the diesel wars.

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2020–Present: 6.7L Power Stroke, 3rd Gen

• Heavily revised version of the 6.7.
• Key features:
  • Strengthened block, new fuel injection system.
  • Variable-geometry turbo optimized for towing and efficiency.
  • 475 hp / 1,050 lb-ft torque at launch (2020).
  • By 2023, output increased to 500 hp / 1,200 lb-ft—making it the most powerful diesel in the heavy-duty pickup segment.
• Reputation: Extremely capable, efficient under load, and a leader in the modern diesel horsepower/torque race.

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Summary of Power Stroke Generations

1. 7.3L (1994.5–2003): Legendary reliability, lower emissions tech.
2. 6.0L (2003–2007): Powerful but plagued with major reliability issues.
3. 6.4L (2008–2010): Twin-turbo, better performance, but poor fuel economy & durability.
4. 6.7L Gen 1 (2011–2014): Ford’s first in-house diesel, reliable, innovative design.
5. 6.7L Gen 2 (2015–2019): Strong refinements, class-leading torque.
6. 6.7L Gen 3 (2020–present): 500 hp/1,200 lb-ft, modern emissions, top of the segment.

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The diesel market has become increasingly competitive, and Cummins has continuously updated the 6.7L Turbodiesel to keep pace. Many of its modifications over time were driven by rising performance demands, which required structural reinforcements to withstand higher stresses. Other updates focused on cleaner emissions, better fuel efficiency, enhanced reliability, or a mix of these factors. The most extensive updates occurred in the 2013, 2019, and 2025 model years.

2009

• Added an access port in the turbocharger turbine housing, allowing VGT vane cleaning without removing the turbocharger for easier servicing.
• Upgraded fuel filter housing and filter element for improved filtration.
• Redesigned water pump inlet housing.
• Updated EGR coolant hoses and fittings.

2010

• Transitioned to a single PCM (engine-mounted ECU) managing both engine and transmission, replacing the previous dual-unit setup.
• Revised fuel filter housing with a quarter-turn drain valve.
• Updated thermostat with a higher 200 °F opening point, slightly raising operating temperature (not interchangeable with older versions).

2011

• Pickup models with the 68RFE automatic gained 150 lb-ft of torque, while horsepower stayed the same. G56 manual trucks saw no performance changes.
• Chassis cab models received SCR emissions aftertreatment, requiring DEF.

2013

• Across-the-board power increases: chassis cab G56 models +15 hp/+40 lb-ft, automatics +20 hp/+140 lb-ft, pickup G56 models +50 lb-ft (no hp increase). Standard output gained 20 hp but stayed at 800 lb-ft.
• A new High Output version debuted for Ram 3500s, adding +15 hp and +50 lb-ft over standard.
• SCR became standard for all pickups (DEF required).
• Mechanical updates included a new camshaft (chassis cabs), redesigned pistons, piston skirt coating, new cooling jets, new vibration damper, updated bedplate, Holset HE300VG turbo, larger EGR cooler, smaller water pump/fan pulley, and a new ECU with more processing capacity.
• AS69RC replaced AS68RC in chassis cabs.

2016

• H.O. engines recalibrated for +35 lb-ft, reaching 900 lb-ft. Standard and chassis cab engines unchanged.

2018

• H.O. torque increased to 930 lb-ft. No changes for standard output or chassis cab.
• Final year for the G56 manual transmission.

2019

• Pickup engines received torque boosts: H.O. from 930 to 1,000 lb-ft and standard output from 800 to 850 lb-ft. H.O. power rose from 385 to 400 hp, making the 6.7 Cummins the first pickup engine to hit 1,000 lb-ft. Chassis cab calibration unchanged.
• Significant redesigns included:
  • New pistons (larger wrist pins, revised bowl geometry, lower friction rings, altered compression ratios).
  • Stronger forged rods and crankshaft.
  • A compacted graphite iron (CGI) block for strength and weight reduction.
  • Updated cylinder head (new springs, valves, rocker arms, larger bolts).
  • Hollow camshaft, new hydraulic lifters, and revised rocker arms.
  • Updated Holset turbo delivering up to 33 psi boost.
  • New exhaust manifold design and turbo relocation.
  • Bosch CP4.2 pump (replacing CP3), raising injection pressure to 29,000 psi.
  • Revised injectors, cooling, lube oil pump, and aluminum housings for oil/water pumps.

2020

• Chassis cab calibration raised to 360 hp (+35) and 800 lb-ft (+50). Pickup engines unchanged.

2021

• Returned to Bosch CP3 pump after CP4 issues; recall issued for 2019–2020 models to retrofit CP3.
• H.O. engines gained +20 hp and +75 lb-ft with a new ECU calibration.
• Standard and chassis cab engines unchanged.

2025

• Ram streamlined the diesel lineup to a single option: the H.O. 6.7 Cummins paired with the ZF PowerLine 8-speed automatic. Pickup and chassis cab models share the same engine but retain different ECU calibrations, with pickups receiving an extra 10 hp.
• Major updates included:
  • Bosch CP8 fuel pump rated to 32,000 psi.
  • Traditional glow plugs replacing the grid heater for cleaner startups.
  • New cartridge-style oil filter.
  • Revised turbocharger.
  • Engine-mounted DOC for quicker light-off and better efficiency.
  • Updated EGR system.
  • New cylinder head with externally mounted injectors for easier servicing.
  • Redesigned intake manifold for better cylinder airflow.
  • Return to a grey cast iron block (no longer CGI).
  • New piston design with lower 16.0:1 compression.
  • ZF PowerLine 8-speed standard across all models.

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Cold weather impacts diesel engines more severely than gasoline engines, and this isn’t solely because of the engines themselves. By design, diesel engines are more difficult to turn over and start, and low temperatures make this challenge even greater. In fact, studies suggest that at zero degrees Fahrenheit, a diesel engine can be up to five times harder to start compared to at 80 degrees. Additionally, other conditions related to diesel fuel also come into play.

Startup Compression Temperatures

Diesel engines ignite fuel using hot air generated by compression rather than a spark, as in gasoline engines. Because air heats up when compressed, diesels rely on much higher compression ratios—often about double those of gas engines—to achieve ignition temperatures. This higher compression makes it more difficult for the starter motor to turn the engine, demanding greater electrical output from the battery. For this reason, many diesel-powered vehicles, especially larger pickup trucks, are equipped with two batteries.

Cold weather worsens the issue since batteries lose a significant amount of their capacity in low temperatures—estimates suggest as much as a 60% drop at zero degrees Fahrenheit compared to 80 degrees. While this power loss impacts both gas and diesel engines, the extra demands of a diesel put even more strain on the battery in cold conditions.

Because compression alone might not heat cold air sufficiently to ignite fuel, many diesels use glow plugs. These small electric heaters, located at the top of the cylinder, warm the chamber before startup. However, glow plugs also consume battery power, meaning the battery must deliver energy before the engine even begins cranking.

Additionally, low temperatures thicken engine oil, increasing friction between moving parts and making it harder to circulate—an issue that affects both diesel and gasoline engines.

Fuel

Both gasoline and diesel engines can be affected by water in the fuel. In cold weather, moisture can condense inside the fuel tank, forming droplets that may mix with the fuel and freeze in the lines, causing blockages. To reduce this risk, it helps to keep the tank at least half full or to use a fuel additive designed to prevent fuel line freezing.

Diesel engines, however, face an additional challenge that gasoline engines do not. Standard No. 2 diesel fuel contains paraffin wax to improve combustion efficiency. Unfortunately, low temperatures can cause this wax to solidify into a gel-like form, which may clog filters and fuel lines. To counteract this, many fuel stations switch to No. 1 diesel—or “winter diesel”—during colder months. This type of diesel is more refined, less prone to gelling, and typically more expensive. In some cases, stations may offer a blend of No. 1 and No. 2 diesel depending on the weather.

Drivers can also use anti-gel additives to reduce the risk of fuel gelling, but these must be added before filling the tank so they mix properly, and ideally before temperatures drop below freezing. Without this precaution, a tank of No. 2 diesel purchased in the fall could end up gelling in the middle of winter.

DEF

Beginning with many 2010 models, diesel vehicles are required to use diesel exhaust fluid (DEF) to comply with emissions standards. DEF is sprayed into the exhaust system, so it doesn’t influence how the engine starts or runs directly. The challenge, however, is that DEF is primarily water and can freeze at around 12°F. To make matters more restrictive, a diesel vehicle will not start if the DEF tank is empty.

Although DEF inside the vehicle’s tank is usually safe from freezing—often thanks to built-in heaters—the same cannot be said for DEF containers stored in a cold garage. If you let the DEF tank run low and then attempt to refill it with fluid that has frozen in storage, you’ll be stuck until it thaws.

Diesel engines, especially in cars and larger pickups, are admired for their fuel economy and towing capability, but these advantages come with added expenses and occasional challenges.

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