What's The MPG For A 6.7 Cummins Engine? Here's What Drivers Say It Gets

Cummins has kept its headquarters in Indiana since the company's founding over a century ago, where it's brought in more than $34 billion in revenue. Much of those profits came from the sale of diesel engines for consumer and commercial use, including the 6.7-liter turbodiesel inline-six. The 6.7-liter Cummins has been around since 2007, and while owners and mechanics have reported some issues with the Exhaust Gas Recirculation and Diesel Particulate Filtration systems, the engine enjoys a solid reputation for performance and reliability.

Larger Cummins diesel engines are used in a variety of commercial semi-trucks from the likes of Freightliner and Peterbilt, while the 6.7-liter I6 is used in RAM 2500 and 3500 pickup trucks and 4500 and 5500 series chassis cabs. Owners of 2023 RAM 2500s with the Cummins diesel have reported to Fuelly an average of 15.8 miles per gallon over more than 300,000 cumulative miles of driving, while the same engine in the 2024 RAM 3500 has provided just 13.9 miles per gallon, albeit with a considerably smaller data set of about 37,500 miles driven. 

2024 and 2025 RAM 1500s aren't available with the Cummins six-cylinder turbodiesel, but Car and Driver got 23 miles per gallon while testing the 2021 RAM 1500. Most owners report slightly lower mileage on RAM 2500s and 3500s, which is to be expected on a bigger truck, especially when towing a trailer or hauling heavy loads. One owner of a 2018 RAM 2500 going by Chadd said he typically got about 17 miles per gallon in his truck but was able to squeeze out about five more by keeping speeds to around 60-65 miles per hour and unhitching his trailer. That's in line with the 16-21 miles per gallon claimed by a dealership in Oklahoma, as well as reports from other owners.

Several RAM 2500 drivers responded to a 2020 forum post polling them for fuel mileage figures for an unladen Cummins-powered pickup, and the consensus was that low 20s were possible if you were gentle on the throttle. A user named rfwalchli responded, " I see an average MPG that varies around 23 to 24 MPH unloaded and not towing." Captainmal from Sundance, Florida, reported figures for different driving conditions, noting that they got 19 miles per gallon in city driving and 23 on the highway in their Cummins-powered truck.