Top 10 Most Reliable Diesel Trucks in North America

Why It’s On The List:

• Built with legendary mechanical simplicity

• Bosch P7100 injection pump is ultra-reliable and mod-friendly

• Routinely exceed 500,000 miles with only basic maintenance

• Manual NV4500 and NV5600 transmissions have proven to be bulletproof

• Demonstrated the best long-term reliability of any diesel pickup

Second-generation Dodge Rams, built from 1994 to 1998, have achieved an iconic status in the diesel world. These trucks marry a classic square-jawed design with an engine known to run “forever.” Under the hood lives a 5.9-liter Cummins inline-six diesel engine.

This generation of engine is known for its overbuilt internals and lack of electronic complexity. It features a cast-iron block and cylinder head, heavy-duty crankshaft and connecting rods, and only two valves per cylinder driven by an in-block camshaft. Use of a gear-driven timing system means there’s no belt or chain to break.

The engine’s simple, fully mechanical fuel system also plays a key role in its reliability. As long as the Bosch P7100 injection pump is fed a constant supply of clean fuel, it has been shown to operate flawlessly for decades. In these years, the 5.9-liter Cummins produced between 175 and 215 hp with 420 to 440 lb-ft of torque, depending on year and application.

Dodge offered its second-generation Ram trucks with a choice of either an NV4500 five-speed manual transmission or the 47RH/47RE four-speed automatic. The NV4500 manual is celebrated as one of the toughest truck transmissions ever built. It features a cast-iron case and a “granny low” first gear. Clutches tend to last an incredibly long time under the Cummins engine’s torque—and it handles additional power quite well, too. The automatics (47RH in 1994 and 1995, and 47RE in 1996-1998), on the other hand, were a known weak link. From the factory, Dodge actually derated the engine by 15 to 25 horsepower in automatic-equipped trucks to ensure longevity. Heavy towing or added power would cause the gearboxes to overheat and slip. Axles—Dana 80 (rear) and Dana 60 (front)—were properly robust.

The 5.9-liter 12-valve Cummins engine itself has very few weaknesses. One well-known issue, however, is the “killer dowel pin.” This tiny alignment dowel in the timing gear housing can vibrate loose and fall into the timing gears, potentially causing catastrophic failure if not addressed. Other minor issues include fuel leaks or hard starting if the mechanical fuel lift pump wears out. No advanced sensors, electronics, or emissions systems means there is very little to go wrong.

This engine is incredibly easy to modify. With a few simple tweaks to the P-pump (turning up the fuel delivery via adjustment screws or installing a new fuel plate), you can gain significant power without sacrificing reliability. It’s common to bump a stock 180-hp engine to 300 or more with just injection pump tuning. Add a tighter turbocharger wastegate and larger fuel injectors and the 12-valve Cummins becomes a serious contender. The truck’s chassis and cooling system are so overbuilt that they will easily accommodate more than 500 hp, which the engine can also manage on factory internals.

Owners of these second-generation 1994 to 1998 Dodge Ram trucks often brag about the Cummins engine lasting more than 300,000 miles. With routine maintenance, it’s not uncommon for this same engine to run well beyond 500,000 miles in industrial applications before needing a rebuild. Dodge sold hundreds of thousands of these trucks, and their reputation for reliability is a major reason why.

2. 2006–2007 Chevrolet Silverado/GMC Sierra 2500HD/3500HD (6.6-liter Duramax LBZ)

Why It’s On The List:

•  Last Duramax Silverado/Sierra produced before the implementation of major emissions control systems (DEF/SCR)

•  LBZ Duramax is built with strong internals, and users have reported minimal failures

• Well balanced between daily drivability and towing strength

• Six-speed Allison 1000 automatic transmission is smooth and robust

• Blends the best of modern reliability with old-school toughness

Despite their brief run, LBZ-equipped 2006 to 2007 GM heavy-duty pickups are widely regarded as the company’s most reliable diesel trucks. The LBZ 6.6-liter Duramax diesel V-8 was a mid-cycle upgrade the debuted in late 2005 (2006 and 2007 model year) Chevy Silverado and GMC Sierra 2500HD and 3500HD pickups. This engine produced 360 horsepower with 650 lb-ft of torque, which was an increase from the previous generation. The LBZ was the last pre-DPF Duramax.

This Duramax generation is beloved for its rock-solid internals and minimal electronic drama. GM strengthened this engine with a stouter block casting, 4-mm-deeper cylinder bores, stronger main bearing caps, and forged steel connecting rods. The LBZ retains the Bosch CP3 high-pressure common-rail injection pump, which offers a stellar reliability record. Cooling and head gasket reliability issues that plagued the LB7 and LLY Duramax engines had been largely eliminated by the time the LBZ was introduced.

Backing the LBZ Duramax is the renowned Allison 1000 automatic transmission. At the beginning of 2006, these trucks sported a five-speed unit; however, a six-speed version with tap-shift was introduced by late 2006. The Allison transmission is a large part of why these trucks earn such a stellar reputation, as they were among the most robust automatics of the time. GM also offered a ZF six-speed manual transmission in some 2006 model year trucks, though it was eliminated from the lineup by 2007. The trucks utilize an AAM 11.5-inch rear axle (similar to what Dodge used), and the front suspension is a robust independent setup.

Diesel enthusiasts often crown the LBZ-equipped 2006 and 2007 GM trucks as the best Duramax pickups to buy. These trucks have a strong following and tend to hold their value well. Many owners regularly report that these trucks run flawlessly past 250,000 miles with little more than basic maintenance. Additionally, the ease of computer tuning on the LBZ (it was the last Duramax generation that did not have the ECU on lockdown) makes it popular among the performance crowd.

3. 1999–2003 Ford F-Series Super Duty (7.3-liter Power Stroke)

Why It’s On The List:

• Built to run forever, often surpassing 400,000 miles with basic maintenance

• Engine features forged internals and a low-stress HEUI fuel system

• Parts are easy to find, and these trucks are easily serviced all across the country

• While not the most powerful diesel engine, it is nearly unkillable

• Workhorse that built Ford’s diesel legacy

Ford first introduced the world to its Super Duty lineup of pickups in 1999. Powered by a Navistar-built 7.3-liter Power Stroke V-8 engine, the Super Duty set a new benchmark for diesel reliability. To this day, used truck buyers seek out 1999 to 2003 Ford Super Duty pickups specifically for the engine. The 7.3-liter Power Stroke is famed for its simple, low-maintenance design and robust construction. The engine is built with a stout cast-iron block and cylinder heads, along with forged steel connecting rods. It features a hydraulic electronic unit injectors (HEUI) fuel system. While electronically controlled, it is highly robust. Ford improved the injectors to 140-cc split-shot units for smoother and quieter operation than the older 7.3-liter IDI engines. Power output ranged from 235 to 275 hp and 500 to 525 lb-ft of torque over the engine’s four-year run.

Backing the 7.3-liter Power Stroke was the choice of two robust transmission options—4R100 four-speed automatic or ZF6 six-speed manual. While both have proven reliable, the manual is sought after for its strength and direct control. Both gearboxes have been shown to last for hundreds of thousands of miles at factory power levels. The axles are equally robust, utilizing either a Dana 50 or 60 up front and a Sterling 10.5-inch or Dana 80 in the rear, depending on year.

The 7.3-liter Power Stroke V-8 has very few weak points. Typical minor issues include camshaft position sensor failures and oil leaks around the high-pressure oil pump or turbo up-pipes. Glow plug relay or controller failures can cause hard cold starts, but those pieces are cheap and easy to replace.

While not quite as easy to make big power as with newer diesel engines, the 7.3-liter Power Stroke has a huge aftermarket following and has been shown to easily push past the 400-hp mark on stock internals. Simple tuners can safely add 50 to 100 hp. Larger injectors, upgraded turbochargers, and fuel system modifications can push output even higher. 

The engine’s heavy cast-iron construction and conservative power output means internal stresses are relatively low. Many owners have reported accumulating 300,000 miles (or more) on the original internals. With good care, 500,000 miles isn’t out of the question. Picking up a used 1999 to 2003 Ford F-Series Super Duty with 200,000 miles is still considered a solid bet.

4. 2001–2004 Chevrolet Silverado/GMC Sierra 2500HD/3500HD (6.6-liter Duramax LB7)

Why It’s On The List:

• LB7 Duramax is built with strong, forged internal components

• Generally lacking in emissions equipment

• Simplified engine electronics and limited sensor dependency

• Allison 1000 transmission is durable and robust

• Known for offering exceptional fuel economy

In 2001, GM introduced the world to its all-new 6.6-liter LB7 Duramax diesel V-8 engine. Developed as a joint venture between General Motors and Isuzu, the LB7 Duramax was GM’s first modern high-speed diesel engine. This represented a monumental leap over the aging 6.5-liter Detroit Diesel engine that it replaced. In stock form, the LB7 produced around 300 hp with 520 lb-ft of torque. Importantly, the LB7 came with no DPF or SCR systems, and only California models had exhaust gas recirculation (EGR). The engine featured aluminum cylinder heads on a cast iron block. It utilized the state-of-the-art Bosch CP3 high-pressure injection pump.

The soon-to-be-famous Allison 1000 five-speed automatic transmission also made its consumer debut with the 2001 Chevy Silverado and GMC Sierra HD pickups. In the early 2000s, having an automatic transmission as stout as the Allison was unheard of. Built to handle the Duramax engine’s torque with ease, it featured full electronic control and adaptive learning. Catastrophic failures are rare, and many LB7-era Allison transmission are still going strong to this day. GM also offered a ZF six-speed manual transmission option for those who preferred more direct control.

The one Achilles’ heel of the LB7 is its fuel injectors. The original design of the LB7 injectors tended to develop cracks in the body or seal leaks, which led to fuel dilution in the oil. GM addressed this by extending the injector warranty to seven years or 200,000 miles, along with updating the design. Some trucks experienced injector harness chafing as well. If not for the injector issues, the LB7 Duramax’s track record was nearly spotless. Many owners consider this a manageable flaw. Once addressed, the LB7 can serve trouble-free for a very long time.

The LB7 quickly gained a reputation for strength and longevity thanks to its relatively low-stress, conservative output figures and robust construction. Many components were shared or derived from Isuzu’s medium-duty engine lineup, leading to an overbuilt quality. With proper care and maintenance, these trucks often run 300,000 miles or more. The combination of smooth power, reliability, and fuel economy makes LB7-equipped trucks a favorite of heavy-duty truck buyers.

5. 2003–2007 Dodge Ram 2500/3500 Heavy Duty (5.9-liter 24-valve Cummins)

Why It’s On The List:

• Runs much cleaner and far quieter than the former 12-valve Cummins

• Early common-rail fuel injection technology is robust and desirable

• Fewer emissions-related issues than the later 6.7-liter Cummins-equipped trucks

• Easily modifiable, capable of handling 500 hp on stock internals

• Solid mid-point in the Dodge/Ram lineup, falling between the raw and refined Cummins engines

In 2003, Dodge introduced a new generation Ram heavy-duty pickup. This truck featured updated styling and a significantly revised 5.9-liter Cummins diesel engine. Most importantly, 2003 ushered in common-rail direct fuel injection for the 5.9-liter Cummins engine. Using a Bosch high-pressure fuel system and CP3 injection pump with electronic control, performance and reliability were significantly improved. In addition to smoother operation and easier starting, this fuel system offered more power without compromising longevity. In fact, the Bosch CP3 high-pressure injection pump has proven to be one of the most reliable diesel fuel systems of all time.

This engine generation retained a cast-iron block and cylinder head along with a forged steel crankshaft and connecting rods. With no exhaust gas recirculation (EGR) and no diesel particulate filter (DPF), this generation of Cummins was the last “simple” modern diesel. These Cummins engines are known to routinely surpass 300,000 miles, with owners reporting that (aside from maintenance) the engine internals last the lifetime of the truck.

Early third-generation Dodge Ram trucks offered the NV5600 six-speed manual transmission (2003–2004), while 2005-and-newer switched to the G56 six-speed manual. Automatics were the 47RE four-speed (2003–2004) and 48RE (2004–2007). The 48RE was an improved version of the 47RE, proven to be reliable with consistent fluid changes. These trucks came fit with an AAM 11.5-inch rear axle and AAM 9.25-inch up front. Transfercases were the stout NP271 or NP273.

These common-rail fueled engines are extremely modification-friendly. Unlike the older 12-valve engines, these are able to be tuned via software, and power gains of more than 100 hp are easily attainable. Impressively, the 5.9-liter’s bottom end can handle more than 600 hp.

Within the diesel community, the 2003 to 2007 5.9-liter Cummins Rams are often considered the holy grail of modern Dodge/Ram trucks. They represent an ideal balance: newer comfort and technology paired with the proven 5.9-liter Cummins reliability. 

6. 2011–2016 Ford F-Series Super Duty (6.7-liter Power Stroke)

Why It’s On The List:

• Ford’s first attempt at an in-house-designed diesel engine

• Solid track record of reliability (after the early turbocharger updates)

• Produces excellent fuel economy while also returning low NVH

• Engines handle high mileage very well (with proper maintenance)

The 2011 model year of Ford’s F-Series Super Duty saw the company’s first in-house-designed Power Stroke diesel engine. After its decades-long partnership with Navistar came to a crashing end thanks to complications with the 6.0-liter and 6.4-liter Power Stroke engines, consumers were excited for Ford’s new 6.7-liter Power Stroke V-8, codenamed “Scorpion.” This engine has been powering the Ford Super Duty ever since.

Ford’s first-generation 6.7-liter Power Stroke produces between 390 and 440 hp along with 735 to 860 lb-ft of torque. The engine features high-pressure common-rail fuel injection, with 2011 to 2014 engines utilizing a Bosch CP4.2 injection pump. Ford switched to the Denso HP4 injection pump in 2015. A unique single-sequential Garrett turbocharger (2011 to 2014) was replaced by a simpler Garrett GT37 unit in 2015. The engine features advanced emission controls, including exhaust gas recirculation (EGR), diesel particulate filter (DPF), and selective catalytic reduction (SCR). Despite the complexity, Ford has managed to make the 6.7-liter Power Stroke very reliable and robust.

By designing it in-house, Ford overbuilt critical components of the engine. It has a compacted graphite iron block (CGI), aluminum heads with six head bolts per cylinder, a forged steel crankshaft, powder-forged connecting rods, and a reverse-flow layout (exhaust inside the V). The engine comes mated to the company’s TorqShift 6R140 six-speed automatic transmission that features a lockup torque converter, PTO provisions, and adaptive shift logic.

All-in-all, Ford’s Super Duty drivetrain with the 6.7-liter and 6R140 is considered nearly bulletproof in the field, with many commercial fleets running these trucks for hundreds of thousands of miles without significant failures. After the stumbles of the 6.0-liter and 6.4-liter Power Stroke engines, the 6.7-liter Power Stroke earned Ford redemption in the eyes of owners. Today, these early 6.7-liter Power Stroke engines have a strong reputation, with many considering them to be on equal footing with Cummins and Duramax engines when it comes to long-term reliability.

7. 2020–2025 Chevrolet Silverado 1500/GMC Sierra 1500 (3.0-liter Duramax I-6)

Why It’s On The List:

• Duramax inline-six configuration offers incredibly smooth and quiet operation

• Frequently return excellent fuel economy, often passing 30+ mpg on the highway

• Paired with a well-engineered emissions system with very few early issues

• Proven to be the most reliable modern light-duty diesel

The only light-duty entry to our list is the thoroughly impressive 3.0-liter Duramax inline six-cylinder found in GM’s 2020 to 2025 Chevy Silverado and GMC Sierra 1500 pickups. A first-generation, codenamed LM2, ran from 2020 to 2022 and produced 277 hp with 460 lb-ft of torque. In 2023, the engine was updated and renamed LZ0. It now produced 305 hp with 495 lb-ft of torque. This engine is constructed with an aluminum block that has iron cylinder sleeves, dual overhead cams, and a forged steel crankshaft. Owners frequently report fuel economy bettering 30 mpg.

GM’s 3.0-liter Duramax is paired with its 10L80 ten-speed automatic transmission. The 10L80 had a few issues when introduced in gas models, such as torque converter shudder, but ongoing refinements and the diesel engine’s smoothness have largely mitigated these.

Maintenance on the 3.0-liter and ten-speed combo is straightforward: oil changes around 10,000 miles and fuel filter changes at about 30,000 miles (which are easy to do). The transmission is filled with long-life fluid (though many will service it around 60,000-100,000 miles as preventive care.) With proper maintenance, expect this powertrain to go the distance—potentially 200,000-300,000 miles—given diesel’s inherently long-wearing nature and the engine’s strong fundamentals.

This engine has swiftly built a reputation among owners, often topping reliability charts for the light-duty segment. In fact, in some consumer surveys, the 2021 and 2022 Silverado 1500 diesel was rated the most reliable half-ton truck powertrain. The engine is quiet and refined, which means fewer tradeoffs in comfort for choosing the diesel engine option. GM’s 3.0-liter Duramax shows that diesel engines can be clean, efficient, and reliable—a combination that hasn’t always been true in the past.

8. 1989–1993 Dodge Ram D250/W250 (5.9-liter 12-Valve Cummins)

Why It’s On The List:

• The OG, the engine that started the diesel pickup revolution

• Incredibly simple rotary-style Bosch VE injection pump

• Low power output is balanced with exceptional longevity—1+ million miles is not unheard of

• While the truck’s body/interior aged poorly, the drivetrain is absolutely rock solid

• Reliable, no-frills, farm truck that everyone craves

The 1989 to 1993 Dodge Ram, commonly called the “first-gen Cummins,” holds a special place in diesel history. This truck is the one that started the consumer diesel craze. Dodge partnered with Cummins to fit its medium-duty 5.9-liter Cummins I-6 turbodiesel into the company’s D250 and D350 pickups, starting with the 1989 model year. These engines made just 160 hp and 400 lb-ft of torque, which is modest by today’s standards. These engines utilized a Bosch VE rotary mechanical injection pump and were paired with a rugged three-speed automatic or five-speed manual transmission. With their simplistic, tractor-like diesel engine, these trucks could easily out-tow and outlast the gasoline trucks of the time.

Essentially a detuned version of Cummins’ proven commercial 6BT engine, this first 5.9-liter Cummins engine features a heavy cast-iron block and head, direct fuel injection, forged steel crankshaft and rods, and 12 valves actuated via pushrods. The lack of any electronics or emissions equipment means there are virtually no gremlins: the engine needs only a 12-volt supply to the fuel shutoff solenoid to run.

The robustness of this engine put Dodge on the map as a serious player in the hard-working heavy-duty truck department. Ford and GM’s diesels of the era (IDIs from Navistar and Detroit Diesel) couldn’t match the Cummins’ durability and torque. Many first-generation Cummins trucks have surpassed 500,000 miles on the original engine, with most owners reporting that the truck’s body will fall apart before the engine.

9. 2017–2025 Chevy Silverado/GMC Sierra 2500/3500HD (6.6-liter Duramax L5P)

Why It’s On The List:

• Stronger cast-iron block, larger crankshaft, and improved pistons

• Durable Denso HP4 injection pump replaces the problematic CP4.2 used in the LML

• New Allison ten-speed automatic transmission

• Much improved DPF, EGR, and SCR emissions control systems

• Larger Garrett variable geometry turbo (VGT) with improved cooling and durability

The Duramax L5P is the latest generation of GM’s 6.6-liter turbodiesel V-8 for its heavy-duty trucks. Introduced for model-year 2017, this engine represents the most significant redesign of the Duramax since its inception in 2001. The L5P launched with 445 hp and 910 lb-ft of torque and over the years has increased to 470 hp with 975 lb-ft.

The L5P has quickly gained a positive reputation for reliability. The block casting is stronger, and the internal rotating assembly (crank, rods, and pistons) have been significantly strengthened. GM switched to an HP4 high-pressure fuel system by Denso, eliminating the embarrassing Bosch CP4 failures of the previous generation.

From 2017 to 2019, the L5P Duramax was backed by a six-speed Allison automatic transmission. In 2020, the company added its new ten-speed 10L1000 Allison automatic. This transmission is actually built by GM with a license to use the “Allison” name. Designed to Allison standard, this transmission has so far not presented any widespread issues. The rest of the drivetrain (AAM 11.5-inch and 12-inch rear axles on 2500HD/3500HD and stout independent front suspension components) are carry-overs that have proven themselves.

Despite being one of the newest diesel engines on the market, the L5P Duramax is rapidly building a solid reputation as one of the best heavy-duty diesel engines. Many long-time Duramax owners who may have been wary of new emissions technology have been surprised by how trouble-free the L5P-equipped trucks generally are. Industry experts have noted that modern diesels like the L5P have achieved reliability levels that rival or exceed simpler old engines. 

10. 1983–1994 Ford F-250 and F-350 (6.9-liter and 7.3-liter IDI V-8)

Why It’s On The List:

• These trucks are very often overlooked but are relatively simple

• Low output but incredibly durable when cooled properly

• There are many of these trucks still running in rural fleets and military applications

• Pure old-school reliability

Before the era of either the Super Duty or Power Stroke, Ford’s F-250 and F-350 pickups came fit with a pair of robust diesel engine options. From 1983 to 1987, the company offered an International Harvester (later Navistar) 6.9-liter indirect injection (IDI) and naturally aspirated engine that produced 170 hp and 315 lb-ft of torque. In 1988, the engine was enlarged to 7.3 liters of displacement, retaining its indirect injection and natural aspiration. It produced 180 hp with 338 to 360 lb-ft of torque. A turbocharger was finally offered in late 1993. While not powerhouses, these engines leave a legacy of simplicity, reliability, and longevity.

With no computers, these engines rely on mechanical fuel injection and glow plugs for cold starts. The block and heads are cast iron, the crankshaft and rods are forged steel, and the engine runs with a relatively high (21.5:1) compression ratio.

These engines came backed by the robust Ford C6 three-speed automatic transmission in the early years, later replaced by the E40D four-speed automatic. Manual transmissions were also offered, with the T-19 four-speed being fit in the early ‘80s and ZF5 five-speed in the later years.

The 6.9-liter and 7.3-liter IDI Fords are fondly remembered as old-school workhorses. These were honest, bulletproof engines that easily surpassed 300,000 miles of service. They may be slower and sootier than today’s diesels, but they delivered dependable service in an era before computers. Owners of these trucks in the ‘80s and ‘90s recall them starting every morning and running all day, every day, with little upkeep. While these engines have a much smaller enthusiast following than the Power Stroke family of engines, they have a cult following of owners intent on keeping them running forever.

Which Diesel Trucks Have the Most Problems? 

2003–2007 Ford F-Series Super Duty (6.0-liter Power Stroke)

The Ford 6.0-liter Power Stroke V-8, which was in use in Super Duty pickups from 2003 to 2007, is widely considered one of the least reliable Ford diesel engines of all time. The engine was flawed from the start due to insufficient testing and poor implementation of emissions systems.

Navistar, the builder of these engines, utilized only four, low-quality, head bolts per cylinder (unlike the six-per-cylinder used in the 7.3-liter Power Stroke), which would often result in bolt stretch and blown head gaskets. The exhaust gas recirculation (EGR) system was also overly complex and poorly cooled. This led to clogged or leaking EGR coolers, which ultimately could result in catastrophic engine failure. There were also issues with the engine’s high-pressure oil system, oil cooler, and fuel injectors. 

2008–2010 Ford F-Series Super Duty (6.4-liter Power Stroke)

After dealing with issues presented by the 6.0-liter Power Stroke engine, Navistar and Ford attempted to right the wrongs with a new 6.4-liter Power Stroke diesel V-8. In use from 2008 until 2010, this engine quickly developed a reputation for being expensive to maintain, complex, and prone to several serious issues.

Chief among the flaws, the 6.4-liter utilized post-injection, which adds fuel late in the combustion cycle to regenerate the diesel particulate filter (DPF). This caused unburned fuel to wash down cylinder walls and enter the crankcase, contaminating the oil. The result was accelerated bearing wear, piston ring degradation, and turbocharger failure. Very frequent oil changes—as often as 3,000 miles—were required. The engine’s complex series-sequential turbocharger also proved problematic, and the engine suffered from a poor cooling system design. There were also rampant head gasket, valve seat, and fuel injector issues. 

2014–2019 Ram 1500 (3.0-liter EcoDiesel)

Ram introduced the world to a new era of diesel-powered half-ton pickups in 2014 with the 3.0-liter EcoDiesel V-6. Initially praised for its torque and fuel economy, the first generation (2014-2019) earned a reputation for unreliability due to a combination of design flaws, emissions-related problems, and costly failures.

This first-generation EcoDiesel engine was prone to bottom-end failures that included rod bearing failure, crankshaft failure, and spun bearings. These typically led to a full engine replacement. The root causes of these included poor lubrication design along with oil starvation in critical areas and relatively weak metallurgy for a diesel application. Turbochargers were also prone to failure due to oil contamination. They also suffered from EGR and other emissions system failures. 

2011–2016 Chevy Silverado/GMC Sierra 2500/3500HD (6.6-liter Duramax LML)

General Motors has seen generally solid success with its line of 6.6-liter Duramax diesel-powered pickups. While the LML Duramax—used in Silverado and Sierra HD trucks from 2011 to 2016—is not universally considered unreliable, it does have one critical design flaw that has tarnished its reputation: the Bosch CP4.2 high-pressure fuel pump.

The LML Duramax introduced the new Bosch CP4.2 injection pump to meet tightening U.S. emissions regulations. However, this pump was originally designed for use in Europe, where low-sulfur diesel fuel is still available. In the U.S., however, the ultra-low-sulfur fuel lacks the proper lubrication needed for the pump. This leads to internal metal-on-metal wear. When the pump fails, it sends metal shrapnel through the fuel lines, injectors, fuel rails, return lines, and even back to the tank. This leads to a costly entire fuel system replacement. 

1999–2001 Dodge Ram 2500/3500 (5.9-liter 24-Valve Cummins)

While Cummins diesel engines are universally praised for their reliability, not every generation has been a hit. The title of “most unreliable Cummins diesel engine” goes to the 5.9-liter “53 Block” Cummins. These engines were used in select Dodge Ram trucks from 1999 to 2001 and had a critical casting flaw that could result in catastrophic block failure.

The “53” refers to a casting number found on the side of the engine block, indicating the block was cast by Mexican foundry TUPY. The issue was an outer water jacket that was too thin. With repeated heat cycles and vibration, the block would crack around the freeze plugs. The best solution was to replace the engine block with a non-53 casting. Since Cummins never issued a recall, owners are left to cover the cost.

Whether you agree or disagree with the trucks that made this list, we can all agree that the diesel truck in your driveway deserves your attention. Find performance parts, products and accessories for your diesel truck at Realtruck.com.