Worst Cummins Engines | Reliability Issues & Problems

Cummins engines are renowned in the diesel world for their power and reliability. The Indiana-based manufacturer has produced engines for various applications, including heavy-duty pickups like the Ram 2500 and 3500 HD, Nissan Titan XD, Isuzu trucks, commercial vehicles, and industrial machinery.

The debate around the blank”>best years for Cummins diesel engines is ongoing. The 12-valve 5.9L 6BT (introduced in 1989) is frequently enough cited as the engine that popularized the Dodge Ram in the diesel market, celebrated for its simplicity and durability. However, not all Cummins engines have been accomplished. The 5.0L Cummins V8 in the discontinued Nissan Titan XD and the early Cummins ISX inline six, which had camshaft issues, are examples of less successful designs. The 5.9L (24-valve) “53-block” was also known for block cracking.

While Cummins is known for its robust diesel engines, some models have experienced notable issues. Here’s a look at some Cummins engines that have presented problems for owners:

• 5.0L Cummins V8 (2016-2019 Nissan Titan XD): This engine, designed to bridge the gap between half-ton and three-quarter-ton trucks, faced complaints shortly after the Titan XD’s 2016 release. Nissan discontinued the Titan XD in 2019.
• 1998-2002 Cummins 5.9L ISB 24-valve: Some Ram trucks with a “53 Block” casting were prone to block cracks, leading to coolant leaks.
• Early Cummins ISX: these engines experienced issues with the EGR valve, cooler, and sensor failure, as well as rocker arm problems that could lead to camshaft damage.

The Cummins 5.0L V8 in the Nissan Titan XD aimed to combine Nissan’s vehicle development expertise with Cummins’ diesel engine prowess.the Titan XD aimed to bridge the gap between the half-ton and three-quarter-ton classes of trucks. However, owners soon reported blank”>problems with the 5.0L Cummins V8 engine.Nissan discontinued the titan XD in 2019 after a short production run.

Common issues included DEF system malfunctions, perhaps due to a failed DEF pump.One 2016 Nissan Titan XD owner reported a $4,800 quote from a dealership for a DEF system part replacement. A 2017 Titan XD owner on the Titan XD Forum reported turbocharger problems, leading to power loss, dashboard codes, and shifting issues while towing. In 2022, blank”>Nissan (PDF) issued a campaign bulletin for an “Emission Warranty Extension” covering 14,269 units, noting potential turbo actuator issues. Owners also reported EGR valve, cooler, and fuel system problems on the 5.0L V8.

The 5.9L engine was an inline six-cylinder engine designed for heavy-duty truck applications. The “ISB” stood for “Interact System,” and the “B” indicated its place in the Cummins B-series. While an improvement over its predecessor, some Cummins 5.9L ISB 24-valve engines built between 1999 and 2002 for blank”>Ram trucks with a 53 Block casting were susceptible to block cracks due to a thin crankcase around the water jackets, causing coolant leaks.

This 5.9L Cummins ISB engine also experienced lift pump failure, leading to fuel system problems, especially with its fuel injectors and a high-pressure Bosch VP44 injection pump (VP), resulting in fuel starvation and power loss. This was a common repair for owners between 1998 and 2002. “Some of the signs of a dying lift pump. You see a boost dropping for no reason. You notice the engine kind of laying down in the upper RPM ranges,” an owner confessed on blank”>cummins Forums.

The Cummins ISX was introduced to meet stricter emission standards. Replacing the N14 Cummins, it was primarily used in Class 8 trucks, as well as industrial, agricultural, and marine applications.While offering improved fuel efficiency, reduced emissions, and increased power, the ISX experienced issues, particularly with systems designed to improve upon the N14. Common problems included EGR (exhaust gas recirculation) valve, cooler, and sensor failure.

the Cummins ISX also had issues with rocker arms, potentially leading to performance loss or camshaft damage. Overheating, which warps the cylinder head and causes the camshafts to operate in a crooked bore, is a leading cause. This damages the bearings and, in some cases, breaks the rocker arms.

The Cummins 6.7L ISB,introduced in 2007,was blank”>featured among the most powerful diesel engines developed at that time for pickup trucks, boasting a towing capability of up to 31,000 pounds (when mated with the AsinAS69RC) on the Ram 3500. It was popular for its tunability and aftermarket modification potential.

The 6.7L turbo diesel engine featured a VGT (Variable Geometry Turbocharger) designed to reduce lag, incorporate exhaust braking, and provide adjustment to the pickup truck’s load demand. Though, the VGT system had issues, including actuator failure or stuck vanes, leading to exhaust brake problems. Emission tech issues with the EGR system were also present. Turbo actuators were a significant concern. One owner with a 2016 6.7L Cummins reported the same issue at just 16,000 miles. Another owner, with a 2014 engine, said their turbo actuator was the only component to fail before reaching 161,000 miles.

Even reliable brands can produce problematic models. For example, Toyota, known for its reliability, blank”>has at least four unreliable engines and Subaru received poor ratings for the Solterra EV. Cummins, like other manufacturers, has had issues with some engines. However, it has a strong reputation for developing reliable engines that can reach a million miles with proper maintenance.

when buying a truck with a Cummins engine, check the VIN for recalls, TSBs, or known issues. Join diesel forums like the Cummins Forum and the Cummins subreddit on Reddit for real-world insights on maintenance and care. Connecting with a local community of diesel truck enthusiasts can also improve your understanding of your truck.