North America started to get a taste for diesel-fueled vehicles in the 1930s. In the first instance, only the largest of commercial vehicles relied on Rudolf Diesel’s namesake invention because diesel engines generate peak torque at low engine speeds.
Indiana-based Cummins was a key driver of commercial-grade diesel engines in the United States of America, with Clessie Cummins demonstrating the diesel’s biggest advantages over 792 miles (1,275 kilometers) from Indianapolis to the New York Auto Show in a Packard sedan. Beyond massive low-down torque, fuel economy is another defining trait.
A more impactful publicity stunt was Clessie and two colleagues doing a coast-to-coast truck run with a fuel cost of merely $11.22 over 3,214 miles (5,173 kilometers). That means around $240 adjusted for inflation, and trucking companies took notice.
But larger-than-life semis and medium-duty trucks are one thing. Medium- and light-duty trucks appeal to different people with different needs, and this market is very lucrative. It all started in the 1960s with the C series from International Harvester, with the half-ton C-100 through the one-ton C-130.
The quiet pioneer was followed by General Motors in the latter part of the 1970s with the problematic Oldsmobile lump, a 5.7-liter naturally aspirated V8 diesel that was replaced by a Detroit Diesel in 1982. Spurred by the Cummins-powered Dodge Ram, diesel pickups really came into their own back in the 1990s, a move that prompted Dearborn’s Ford Motor Company to adopt Navistar’s 7.3-liter IDI.
The IDI evolved into the direct-injected Power Stroke, and the second-largest automaker of the Detroit Big Three continues to use this branding for its hard-working diesels. Over at General Motors, the Duramax moniker is now used for two distinct mills that serve half-ton and heavier-duty trucks.
As of this writing, the Detroit-based automaker stands out from its closest peers by offering a turbo diesel in half-ton pickups, those models being the Chevrolet Silverado 1500 and mechanically similar GMC Sierra 1500. Ford and Ram also offered six-cylinder mills in the F-150 and 1500, yet both optional diesels were discontinued over slightly different reasons.
The 3.0-liter Power Stroke was canned over low sales, and the high demand for the 3.5-liter PowerBoost gasoline hybrid powertrain, whereas the 3.0-liter EcoDiesel faced regulatory problems over emissions. In other words, the 3.0-liter Duramax of the Silverado 1500 and Sierra 1500 is the only diesel that you can get nowadays in a half-ton pickup truck.
Better in terms of longevity than gassers due to blocks and internal components designed to handle much higher compression, diesels have to be serviced regularly to maintain dependability. Their weakest of points are high upfront costs over equivalent gasoline engines and the complex emissions system, which is the single biggest source of downtime.
Over 100,000 miles of driving, a figure that can be read as nearly 161,000 kilometers in metric speaking places, the Silverado 1500 with the 3.0-liter Duramax offers better total cost of ownership compared to the 6.2-liter small block. Including the upfront costs, fuel savings, maintenance penalty, and resale premium, the advantage is $6,000 or thereabouts.
Having cleared that up, let’s kick this off with the six-cylinder Duramax of the Chevrolet Silverado 1500 and GMC Sierra 1500. After the light-duty diesel engine, we’ll take a closer look at heavy-duty trucks and their significantly punchier diesel engines.
General Motors half-ton pickups with 3.0-liter Duramax turbo diesel I6 muscle
Starting at $53,540 for the 2026 Chevrolet Silverado 1500 or $56,135 for the 2026 GMC Sierra 1500, the smallest member of the current Duramax family is also found in full-size utility vehicles. Originally called LM2, then upgraded to LZ0 specification, the 3.0-liter Duramax was primarily developed by General Motors and Opel in Turin, Italy.
Related in terms of architecture to the Opel brand’s 1.5- and 2.0-liter diesels from that era, the six-cylinder Duramax is assembled in the United States at Flint Engine Operations in Michigan. From the outset, General Motors wanted a balanced yet stout motor, thus explaining the inline design. The folks at GM then decided on cast aluminum for the block.
Augmented with iron cylinder liners, the aluminum blocks are just around 25 percent lighter than comparable iron blocks, therefore leading to increased fuel economy. To handle the high pressures of diesel combustion, the 3.0-liter unit benefits from robust internals, beginning with forged steel connecting rods and the forged steel crankshaft.
Gradually replaced by the LZ0 after the 2023 model year, the LM2 uses seven nodular iron main bearing caps. Boasting a deep-skirt design for extra stiffness, the LM2 is also listed by General Motors with a 15.0:1 compression ratio, aluminum for the lower crankcase extension, and 1-5-3-6-2-4 for the firing order.
Capable of 5,100 revolutions per minute, the LM2 further prides itself on hypereutectic aluminum pistons, a thick piston crown, and a reinforced top ring groove. With the changeover to the LZ0 specification, the manufacturer switched to steel pistons that are slightly narrower than the aluminum design.
This change allowed General Motors to revise the combustion bowl shape. Combined with new fuel injectors, the optimized air/fuel mixture allowed GM to extract more power and torque without compromising the engine’s long-term durability. A revised turbocharger needs to be mentioned as well.
The diesel oxidation catalyst was moved closer to said turbocharger to heat up more quickly, a solution that improves the efficiency of the emissions system at startup. Despite being more potent, the fuel efficiency has been maintained. In combination with rear-wheel drive, the LZ0 drinks a combined 26 miles per gallon (9 liters per 100 kilometers) in the EPA test cycle.
One mile per gallon more efficient than the Ford F-150 PowerBoost, the Silverado 1500 Duramax and Sierra 1500 Duramax are capable of towing 13,300 pounds (6,033 kilograms) when properly equipped. To achieve this rating, the Duramax has to be fitted to a double-cab truck with rear-wheel drive, the standard bed, and the Max Trailering Package to boot.
As noted earlier, prospective customers will have to spend more than $50,000 for the most basic Duramax specifications of the Silverado 1500 and Sierra 1500 for model year 2026. That specification is double cab, standard bed, LT or Elevation trims instead of more work-oriented grades, and front bucket seats instead of the 40/20/40 bench seat with a storage cubby.
Connected to a 10-speed automatic, the Duramax is joined by three gasoline options in the form of the base 2.7-liter TurboMax four-cylinder and two naturally aspirated V8s with displacements of 5.3 and 6.2 liters. Only the TurboMax is equipped with an eight-speed, whereas the V8s are 10-speed only.
While not as powerful as the 6.2-liter small block, 305 horsepower is plenty enough for the Duramax in this application. Its peak torque of 495 pound-feet (671 Newton-meters) puts the LZ0 ahead of the L87, which puts out 460 pound-feet (624 Newton-meters) in optimal conditions on 91-octane gasoline.
The V8s, however, aren’t the secret to maximum payload in the Silverado 1500 and Sierra 1500. To achieve the advertised 2,260 pounds (1,025 kilograms) of payload, customers have to get the regular cab with the long bed, rear drive, WT grade, and the 2.7-liter TurboMax inline-four lump.
The Chevrolet Silverado HD and GMC Sierra HD with the 6.6-liter Duramax turbo diesel V8
Priced at $9,990 over the L8T naturally aspirated V8, the L5P turbo diesel V8 also features Duramax branding. The L5P is the latest evolution of a 6.6-liter engine that General Motors developed in partnership with Japanese diesel specialist Isuzu. The folks at DMAX produce this engine in Moraine, Ohio.
LB7 is what GM calls the first version of the Duramax V8, which relied on Bosch common-rail injection. The switch to Denso common-rail injection occurred with the L5P in 2017, with the L5P flaunting two distinct generations. The second iteration rolled out for model year 2024 with 25 additional horsepower and 65 extra pound-feet of maximum torque.
More responsive under heavy load, the revised L5P includes a redesigned Denso HP4 fuel pump that goes all the way to 2,200 bar (32,000 pounds per square inch) as opposed to 2,000 bar (29,000 pounds per square inch) for the original. To safely contain the increased pressure, GM reinforced and thickened the fuel rails. The Denso-supplied fuel injectors were also changed for higher-flow units in the L5P Gen 2.
Fitted with a BorgWarner variable geometry turbocharger with 10 instead of 11 blades for a larger mass flow area, the 6.6-liter engine had its exhaust valve springs upgraded to withstand higher exhaust back pressure generated by said turbocharger. The snail in question also had its variable vane mechanism improved by changing from 13 smaller vanes to 11 larger vanes for improved vane geometry.
New pistons with a revised combustion bowl design, slightly different layering for the head gasket, and revisions to the internal water jacket structure within the cylinder heads pretty much round off the list of improvements over the L5P from the 2017 through 2023 model year. Challenging the Ram HD’s Cummins I6 in terms of longevity, the Duramax V8 outsells the Power Stroke V8, but only just.
GM also happens to sell more full-size trucks than both rivals, with Ford moving 620,580 such vehicles in the first nine months of 2025 as opposed to 690,056 units of the Silverado and Sierra. The Ram truck brand’s HD line is dead last with 119,122 deliveries in the US market in the analyzed timeframe.
Durable and refined, the L5P Gen 2 available in the Silverado HD and Sierra HD is paired with
“the proven Allison 10-speed automatic transmission.” Said words come from the press releases for the 2024 model year, but GM is misleading here. You see, the Allison-branded 10L1000 is a GM transmission rather than a proper Allison torque-converter auto.
Mercifully, the branding partnership will end on December 31, 2025. Customers who are willing to enter the commercial vehicle realm with the Silverado 4500 through Silverado 6500 are presented with a true Allison transmission. Listed with six forward ratios, the Allison 1000/2000 series of the Silverado MD was engineered for commercial-grade longevity.
An extra on all trims of the heavy-duty Silverado and Sierra, the Duramax V8 can be combined with the regular cab or long bed, double cab with either bed option, and the crew cab with either bed option. The diesel engine is required to hit GM’s advertised 36,000 pounds (16,330 kilograms) of maximum towing capacity.
The Duramax plays second fiddle to the L8T small block when it comes to maximum payload, but not by much. To achieve the best payload rating possible, as in 7,237 pounds or 3,283 kilograms in metric speak, customers have to specify the 6.6-liter gasoline V8 with the lightest cab, the longest bed, dual rear wheels, and rear drive.
Ram’s inline-six turbo diesel heavy-duty pickups
Priced $12,595 over the standard 6.4-liter HEMI naturally aspirated V8 as of this writing, the Cummins inline-six turbo diesel is a 6.7-liter icon of the segment. Stellantis-controlled Ram introduced an extensively revised Cummins for model year 2025, with said revision also including a TorqueFlite HD eight-speed automatic instead of the former Aisin units with six forward ratios.
The Ram-quoted 70 percent increase in torque delivery is astounding, with lower engine RPMs at highway speeds improving fuel economy. But alas, the Environmental Protection Agency does not publish fuel economy ratings for heavy-duty trucks due to unique challenges that make a standardized test nearly impossible to create.
In regard to engine revisions, the ISB had its block and cylinder head extensively redesigned for enhanced structural integrity and superior cooling. Heavier-duty pistons also need to be highlighted, along with a new intake manifold, larger intake and exhaust valves for improved port flow, and the Bosch-supplied CP8 high-pressure fuel pump instead of the earlier CP3 and CP4.2 assemblies.
Featured in 2019 through 2020 models, the CP4.2 is known to fail due to insufficient lubrication. This version of the high-pressure fuel pump features a dual-plunger design with roller tappets and cam lobes that rely on diesel for lubrication. Ultra-low sulfur diesel may be cleaner for the environment, but reduced lubrication properties lead to excessive metal-on-metal friction in the CP4.2 pump.
For model year 2025 and newer trucks, the Cummins engine comes with glow plugs instead of the restrictive grid heater from before. Speaking of which, the grid heater bolt of 2024 and earlier Cummins-powered trucks may fail due to a variety of causes, in which case it may fall into the intake manifold.
The Cummins engine also switched from spur to helical gears to reduce noise, vibration, and harshness. Another way to easily tell the 2025 Cummins apart from its forerunner is top-side access for both fuel filters and the oil filter, namely a cartridge-style oil filter instead of a spin-on metal canister.
When equipped with the rather pricy Cummins, the 2026 Ram 2500 HD tows up to 20,000 pounds (9,072 kilograms). The payload for the gas-fed HEMI is 3,930 pounds (1,783 kilograms). Upgrading to the 3500 results in maximum towing and payload ratings of 36,610 and 7,590 pounds, respectively, figures that can be read as 16,606 and 3,488 kilograms.
Ram says the high-output Cummins of the 2500 and 3500 makes 430 horsepower at 2,800 revolutions per minute and 1,075 pound-feet (1,458 Newton-meters) at 1,800 revolutions per minute, putting it ahead of the Duramax in terms of maximum torque (975 lb-ft or 1,322 Nm) despite a 40-horsepower deficit.
Truth be told, peak torque is king in this application and larger commercial vehicles. Horsepower is a measure of how fast a given engine can do the work, and torque is the measure of the work itself.
The segment-leading Ford F-Series Super Duty with the 6.7-liter Power Stroke turbo diesel V8
Easily the most capable heavy-duty pickup in North America, the Super Duty line of the F-Series can be had with a base 6.8-liter gasoline V8, a beefier 7.3 called Godzilla, and the 6.7-liter Power Stroke turbo diesel V8 in regular and punchy flavors. The latter offers the most power and most peak torque of any heavy-duty pickup truck for model year 2026.
Priced at $13,495 over the 6.8-liter naturally aspirated V8 or $2,500 higher than its standard-output version, the high-output Power Stroke is compatible with B20 fuel, with 20 indicating the maximum percentage of biodiesel. B20 offers reduced tailpipe emissions of carbon monoxide and particulate matter, and biodiesel has superior lubricity.
On the other hand, this fuel has a slightly lower energy content per unit of volume compared to petroleum-only diesel. As expected, B20 requires proper attention in extremely cold weather. Diesel contains paraffin wax, a component that is naturally present in crude oil. This component crystallizes at cold temperatures, while gasoline does not contain the long-chain hydrocarbon compounds.
Available from the F-250 XL up, the high-output Power Stroke was introduced for the 2023 model year with many hardware and tuning changes from the standard output. From the redesigned turbocharger to the lower compression ratio, more robust injection system, cast stainless-steel exhaust manifolds, and unique steel pistons, a lot of things help the high-output engine pull heavier loads than its brother.
Ford’s consumer website for the US market reads up to 40,000 pounds (18,144 kilograms) for gooseneck towing, a rating made possible by the F-450 XL regular cab 4×2 with dual rear wheels and the high-output Power Stroke. Maximum power and torque are achieved at 2,600 and 1,600 revolutions per minute, respectively, with Ford claiming 500 horsepower and 1,200 pound-feet (1,627 Newton-meters).
The standard-output Power Stroke is no slouch. Available at similar engine speeds, the maximum output numbers are 475 horsepower and 1,050 pound-feet (1,424 Newton-meters). Beyond the Super Duty line of trucks, the Power Stroke is also found in the F-650 and F-750 medium-duty workhorses.
Internally referred to as Scorpion, the 6.7-liter Power Stroke turbo diesel V8 makes anything from 270 to 330 horsepower and 800 to 850 pound-feet (1,085 to 1,152 Newton-meters) in the F-650 and F-750. Sadly, this engine isn’t available in the 2026 Ford E-Series cutaway and stripped chassis.
As opposed to the 10R1000 automatic of the 6.8-liter gasoline V8, the larger Godzilla engine and both versions of the Power Stroke level up to the 10R140. In the F-450, the high-output Power Stroke is joined by a 4.30:1 axle ratio to achieve the advertised 40,000-pound maximum gooseneck tow rating.
Diesel is preferred by an estimated 65 to 75 percent of heavy-duty truck customers in the United States, depending on how you define heavy-duty trucks. While naturally aspirated V8s of the SOHC variety make plenty of sense for more casual buyers, those who are truly intent on high yearly mileage or heavy towing are better off going the diesel route.
