Is The 6.7L Cummins Diesel A Good Engine? Here's What Owners And Mechanics Say

While Clessie Cummins and business partner William G. Irwin didn't invent the diesel engine, they saw its budding future and in 1919 started Cummins Engine Co. The diesel engine has undergone several changes and enhancements over the last century, paving the way for more robust and efficient designs. While turbocharged variants of the diesel were first incorporated into trucks in 1954 by MAN and Volvo, the idea didn't become widely popular until the '90s. The 5.9L Cummins turbo diesel was the first to start the trend in the Dodge Ram and continues to this day with the impressive high-output 6.7L Cummins turbo diesel I6.

The engine debuted in 2007, replacing the 5.9L iteration and improving stock power output. While there's still a debate as to which is the better diesel between the two, the 6.7L began with 350 horsepower and brawny 650-pound feet of torque. The latest version, the high-output 6.7L Cummins turbo diesel comes out of the factory with an impressive 420 horsepower, and 1,075-pound feet of torque. While its power is notable, the 6.7L Cummins isn't without problems. 

The two emission systems, an Exhaust Gas Recirculation (EGR) and Diesel Particulate Filter (DPF), have reportedly required repairs, significantly hampering performance and emissions. There have also been several recalls, with some owners expressing concerns, but the majority of customer reviews still overwhelmingly recommend the RAM with the 6.7L Cummins turbo diesel engine.

In addition to raw power, one of the notable features of the 6.7L Cummins engine is its intelligent exhaust brake aided by its variable geometry turbocharger. An exhaust braking system helps drivers hauling heavy loads over steep downgrades to maintain a reasonable speed. A truck with a loaded down trailer is much heavier than the average vehicle, and the additional weight makes it especially hard on brakes when going down hills.

The system in the 6.7L Cummins helps control speed bolstered by the back pressure of the turbocharger, so that drivers won't need to worry about overusing their brakes or traveling too fast down a mountain road. One of the dangers of aggressively braking, is something called brake fade, which is when excessive heat begins to prematurely age the components that bring your vehicle to a stop. Not only is utilizing an exhaust brake excellent for navigating hilly terrain, but it can also help ensure your regular brakes last longer. The turbocharger is one reason the Cummins diesel has become so much more efficient in recent years. 

First introduced in 2007, the DPF system was developed to help the engine adhere to stricter emission requirements while still improving output. This technology includes a special filter that stops byproducts, like soot made by the diesel engine, from expelling into the air. Unfortunately, this filter can clog up easily and leave the engine struggling to breath and negatively affected performance. Fortunately, since 2013 it hasn't been as much of an issue, but be aware that 6.7L Cummins prior to that are more susceptible.

Another common issue mechanics have mentioned, is an exhaust back pressure error code, that typically is a result of the system being clogged. Unfortunately, many owners just replace the sensor, thinking that it's the cause of the issue, when in fact the pipe is plugged up. If the sensor is the culprit, it's recommended to replace it with a more expensive premium quality part versus some of the discount parts available for better performance.

Owner reviews of the 6.7L Cummins turbo diesel vary depending on the year, but don't dip below 4.1 out of five from the years 2013 up to 2023, per Cars.com. The 2013 RAM 2500 is one of the worst rated years, with customers stating grievances like, "Money Pit" and "A dozen factory recalls and still climbing." Although, other owners praised the performance, ride, and towing capability, rating it highly. Despite some of the negative comments, the 2013 RAM 2500 is still recommended by most owners.

It's too soon to tell what owners of the newest RAM trucks equipped with the 6.7L Cummins turbo diesel think. But sales of RAM trucks surpassed nearly 46,000 in 2023, and although they haven't completely recovered to pre-2020 levels, did improve from 2022's 45,023 figures, per Good Car Bad Car. If you are interested in getting a vehicle with the Cummins diesel, fans say these are the 5 best years for Cummins Diesel engines and for good reason.