5 Of The Most Notoriously Unreliable Diesel Trucks Ever Made

Ever since the first diesel truck appeared more than a century ago, diesel engines have had a constant presence in the pickup market. These engines are known to be durable, more fuel efficient, and even offer better resale value than their gas counterparts. 76% of commercial trucks currently run on diesel, and 57% of them are at near-zero emissions.

However, diesel trucks are known to have their own set of issues, many of which can be challenging and expensive to repair. While some are maintenance-related, others are inherent due to manufacturing flaws. For instance, the exhaust gas recirculation (EGR) system, designed to reduce emissions, is notorious for failing in many engines due to malfunctioning sensors. Diesel truck owners also often complain of overheating, fuel contamination, and fuel injector clogging.

Manufacturers have replaced some of these defective engines on newer models, but if you're purchasing a truck, especially a used one, there's still a chance you'll end up with these issues, so it's best to keep an eye out for the red flags — especially if they concern one of these notoriously unreliable diesel trucks.

The Ford F-250 once came equipped with a 6.0-liter Power Stroke diesel engine, available in models produced from 2003 to 2007. This second-generation powertrain was introduced to meet stricter emission standards, increase power output, and reduce engine noise. It offered a more advanced fuel-injection system and variable geometry turbocharger technology. However, trucks that housed this engine turned out to be very problematic.

One of the most notorious problems with this truck is its head gasket failure. The head gasket is located between the cylinder head and engine block, and acts as a sealant to prevent fluids from leaking. While this component itself isn't the problem, the bolts that fasten the heads to the block have been known to stretch too far and lose clamping ability, causing the head gasket to blow.

Other components known to have a fair share of problems are the EGR cooler and the fuel injector control module (FICM). So trucks with this engine often experience problems like engine overheating and difficulty starting. The 2006 Ford F-250, in particular, has the most complaints of any Ford F-250. Besides its engine issues, it is also notorious for the "death wobble," where the truck shakes violently and causes a loss of control.

The Chevrolet Silverado 2500 is well known for using GM's most reliable Duramax engines. These diesel engines are a product of the combined efforts of General Motors and Isuzu. The collaborative venture, known as DMAX Limited, was subsequently fully acquired by General Motors, and the 6.6-liter LML Duramax was the first engine produced after this takeover. It was available on 2011-2016 models.

While this truck had its perks, it has also accumulated a generous number of complaints thanks to its engine. There are issues with the NOx sensor, particularly in the first batch of LML engines, for which the company made efforts to rectify by issuing replacements. The engine also used the Bosch CP4.2 fuel pump, which is susceptible to fuel contaminants that result in costly damage. As such, the engine's lifespan is short on most vehicles. This issue eventually led to a lawsuit, and GM had to pay $35 million in the resulting settlement.

The 2015 model might just be the worst Chevrolet Silverado 2500 to invest in, especially when you consider other its problems, like the power steering failure and AC issues. The truck has accumulated 250 complaints and 18 recalls according to NHTSA. After the LML Duramax went off the market in 2016, it was replaced by the more reliable and durable 6.6-liter L5P, which solved some of these problems with a new fuel system and improved cooling.

The Dodge Ram 1500 is generally not a terrible truck, but some of its model years are best avoided, or they'll probably cost you more in repairs than you should have to deal with. Models from 2012 to 2019, which came with the now-discontinued 3.0-liter EcoDiesel V6, have a high volume of complaints, but 2014 takes the cake. It's probably worst model year of the Ram 1500.

One of the common issues with this engine is oil cooler failure. Oil cooler leaks cause the engine oil to mix with the coolant. This can affect engine temperature, cause wear-outs, and ultimately hamper performance. The 3.0-liter EcoDiesel V6 also used the Bosch CP4.2 fuel pumps, which became notorious for their high failure rate. Ram eventually issued a recall for this defect in 2022.

Moreover, the exhaust gas recirculation cooler has been an issue of concern in 2014-2019 Ram 1500 trucks. Although Ram also issued a recall after acknowledging that the parts were defective, owners have initiated a class action lawsuit claiming that this issue persisted and could cause truck fires.

Perhaps even more problematic than the 6.0-liter Power Stroke is the 6.4-liter engine. Featured in the Ford F-250 Super Duty truck from 2007 to 2011, expectations were high for this one following its disappointing predecessor, but it turned out to be an even bigger letdown.

The 6.4-liter Power Stroke pushed out 350 hp and a peak torque of 650 lb-ft, but while that power is impressive, the engine is also riddled with problems. It is known for its radiator leaks, which makes it prone to overheating. Also, it is common for fuel to seep into the engine oil, preventing proper lubrication of engine components and consequent wear and tear.

On top of that, F-250s powered by the engine are known to have poor fuel mileage. This was linked to the diesel particulate filter (DPF)'s high fuel consumption. Removing the DPF is illegal in some places, so even addressing this issue can be a major challenge if at all possible. The 2008 to 2010 F-250 models all have average reliability ratings on JD Power. However, things noticeably pick up in subsequent years, following the arrival of the more advanced 6.7-liter Power Stroke engine.

Another diesel truck that has earned a bad reputation is the Nissan Titan XD, particularly the models that have the 5.0-liter Cummins V8 Diesel. Cummins is a major player in diesel engine production, so expectations were understandably high. This engine was available on the 2016 to 2019 model years before it was taken off the Titan. During this period, the 5.0-liter V8's numerous complaints earned it a poor reputation.

Like many diesel engines, this engine suffers EGR cooler problems, making it prone to cracking and internal leaks. The valve also tends to accumulate carbon buildups, which results in poor engine performance. In addition, the Titan XD has fuel system-related issues and is vulnerable to transmission problems.

Many owners have reported poor acceleration, stalling, and poor fuel efficiency on their Titan XD trucks. In 2023, federal safety regulators launched an investigation into the engine following the numerous complaints. The investigation includes up to 39,000 trucks released from 2016 to 2019.

This list was compiled based on complaints and owner reviews on Car Complaints, reports from the NHTSA, and reviews from professionals, including our own here at SlashGear. We considered the number and severity of issues on these diesel trucks, many of which are associated with their engines.