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6.7L Cummins Engine Profile

By November 14th, 2021No Comments

The new Cummins 6.7L diesel engine is the latest of the company’s B series engines. Cummins introduced its 6.7L diesel engine in 2007 to replace the popular 24-valve 5.9L ISB diesel engine, which retired in the wake of increased global emissions regulations.

This 6.7L Cummins diesel engine guide is a part of our Diesel Engine Guide series to help with buying a school bus for sale.

This article will dive further into the 6.7L Cummins engine including:

  • Engine Overview
  • Engine Specs
  • Towing Capacity
  • Life Expectancy
  • Maintenance Requirements
  • Typically paired transmissions
  • Common engine problems
  • Engine comparisons to the 5.9L Cummins and 6.7L Powerstroke

6.7 Cummins Engine Overview

The Cummins 6.7L diesel engine continues the 30-year-plus partnership with Dodge as the dedicated powerplant for RAM trucks, including 2007 to present model year RAM 2500, RAM 3500, RAM 4500 and RAM 5500. Prior to the Cummins 6.7L diesel engine’s introduction, Dodge RAM trucks were powered by the Cummins 5.9L turbo diesel engine, beginning in the 1989 model year. The Cummins 6.7L diesel engine also was used to power 2007 to 2015 model year Ford F-650 and Ford F-750 Super Duty trucks. It powered additional vehicles, including chassis cabs, medium-duty vehicles, motorhomes, and school buses built for Blue Bird Vision, Thomas Saf-T-Liner C2, and IC Bus CE.

More than 40 percent of the Cummins 6.7L diesel engine’s internal components carried over from the Cummins 5.9L diesel engine. A side benefit of the partial common design is the high availability of replacement components in the aftermarket.

While made to comply with stricter emissions mandates, the Cummins 6.7L diesel engine offers more power than previous engine models. The inline-six turbo diesel engine is offered in two variants: a standard version with 350 horsepower and 800 pound-feet of torque and a more powerful version with 420 horsepower and 1,075 pound-feet of torque. Depending on the amount of power desired, Dodge RAM consumers have a choice of three transmissions pairings in earlier model year trucks. Cummins claims it is the first light-duty truck diesel engine to exceed 1,000 pound-feet of torque. (In comparison, the 2020 Ford 6.7L Power Stroke V8 turbo diesel engine reaches 1,050 pound-feet of torque.)

The Cummins 6.7L diesel engine features other improvements to support the new higher output ratings, including a high-pressure common rail injection system, a compacted graphite iron engine block, and a new cast-iron cylinder head containing high-temperature capable exhaust valves. Additionally, the Cummins 6.7L diesel engine has a new exhaust gas recirculation (EGR), a diesel particulate filter, and a variable geometry turbocharger (VGT) to reduce turbo lag.

When it comes to emissions-related components, the Cummins 6.7L diesel engine is in the same boat as other diesel engines with performance issues. Compared to its predecessor, the Cummins 6.7L diesel engine is more prone to turbocharger issues, EGR system problems, and head gasket failures. However, mechanics report with proper maintenance the Cummins 6.7L diesel engine can run from 250,000 to 350,000 miles.

6.7 Cummins Engine Models

Engine variationsProduction YearsHorsepowerTorque


Cummins 6.7L diesel engine


2007 to present 2007 to current Dodge RAM 2500, 3500, 4500, 5500 trucks

2007 to 2015 Ford F-650, F-750

Various other medium-duty truck, motorhomes and school buses

Low: 350 hp @ 2800 RPM High: 420 hp @ 2800 RPM



Low: 800 lb-ft @ 1700 RPM High: 1075 lb-ft @ 1800 RPM

6.7 Cummins Typical Transmissions

In Dodge RAM trucks, the Cummins 6.7L diesel engine is paired with three transmissions, including the Cummins 68RFE six-speed automatic, Mercedes G56 six-speed manual and Aisin AS69RC six-speed automatic.

The Aisin AS69RC has only been offered in the high output variant of the Cummins 6.7L diesel engine for RAM 3500 models. The Mercedes G56 manual transmission was offered through the 2018 model year, and it likely retired due to a lack of interest based on the engine’s lower power ratings.

Towing with a 6.7 Cummins

The Cummins 6.7L diesel engine has a towing capacity range from 4,000 pounds to 20,000 pounds, depending on engine-transmission pairings. The most powerful combination is the 6.7L Cummins Turbo diesel engine paired with an Aisin transmission.

6.7 Cummins Engine Life Expectancy

Mechanics report that if properly maintained, the Cummins 6.7L diesel engine could run for 250,000 miles before requiring a major repair or rebuild. In some cases, the engine has reached 350,000 miles.

6.7 Cummins Engine Maintenance Requirements

Maintenance is critical to avoid common failures in the Cummins 6.7L diesel engine. In addition to a regular maintenance schedule, mechanics recommend an occasional oil analysis to confirm fuel dilution.

6.7L Cummins Oil capacity: 12 quarts

Engine variationsNormal conditions


Cummins 6.7L diesel engine
Engine oil & air filter: 15,000 miles/12 months
Fuel filter: 15,000 miles
Engine coolant: 150,000 miles/10 years
Transmission fluid & filter: 120,000 miles

Common Engine Problems

Issues with the Cummins 6.7L diesel engine often come down to emissions parts. Mechanics note that certain years may be more prone to issues, specifically the earlier models of Dodge RAM trucks. These are a few common issues:

  • Diesel particulate filter (DPF) clogging – These clogging issues were more problematic in earlier years of production. The issue causes a build-up of back-pressure for the engine, which can lead to more heat and stress on the engine. Symptoms include power loss, reduced power mode, long cranks, and engine fault codes. Even a refurbished 6.7L DPF can cost more than $1,000, while original filters are nearly double in cost. Some mechanics say they eliminate the issue by washing out the clogged diesel particulate filters, while others opt to delete the DPF completely. However, DPF deletes may come with some legal concerns due to emissions.
  • Turbocharger failures – These issues are more common on earlier model Cummins 6.7L diesel engines, but it can happen on any model year due to the rigorous nature of turbochargers. As turbochargers age, they develop a few side issues, such as leaking oil seals, worn bearings, sticking variable-geometry turbochargers (VGT) and turbine wheel damage. If ignored, the turbine or compressor when may contact the turbocharger housing and result in complete failure. Symptoms include slow spool, excessive exhaust smoke, whining sounds and sudden oil loss. Mechanics recommend idling the truck for a few minutes before shutting down the engine, as well as allowing the oil to reach operating temperatures before pushing the truck too hard.
  • Head gasket problems – While not common, these issues can occur because of the higher power and torque of the Cummins 6.7L diesel engine. High cylinder pressure may be to blame. Symptoms of a blown head gasket include white smoke with a sweet smell, oil mixed with coolant and overheating.
  • Fuel dilution issues – Some fuel dilution in oil is natural, because it’s the way engine manages regeneration and burns particulates for cleaner emissions. Mechanics report a dilution rate of five percent is acceptable. However, some Cummins 6.7L diesel engines seem to have too much dilution, and the issue can interfere with oil lubrication to protect the engine. The issue can result in premature wear of the internal engine. Symptoms of fuel dilution are hard to detect, so it’s a good idea to conduct an occasional oil analysis. Other ways to prevent the issue include avoiding extended idling and allowing the engine to properly warm up, especially before heavy towing.
  • Exhaust gas recirculation (EGR) cooler problems – These issues are common among many other modern diesel trucks, especially within engines with high mileage. Sometimes cleaning the EGR valve will prevent issues.

Cummins 6.7L vs. Cummins 5.9L

5.9L Cummins Engine in a School Bus

The Cummins 5.9L diesel engine was popular among Dodge RAM truck owners, due to its reliability and strength. It is often compared as a benchmark against its successor, the Cummins 6.7L diesel engine. Both Cummins diesel engines have strong brand associations with RAM medium- and heavy-duty trucks that have lasted more than 30 years in manufacturing partnerships.

The Cummins 5.9L (or B Series diesel engines) went into production in 1984 for use in agricultural equipment. Known as the 6BT or 12-valve 5.9L, the engine was a popular alternative to large gasoline V8 engines. In 1998, Cummins replaced the 6BT with the 24-valve 5.9L ISB (Interact System B), which was designed for improved fuel economy and emissions.

Despite its smaller size, Cummins turbocharged diesel engines could produce significant power with decent torque at low engine speeds. The mechanical 5.9L was given a life expectancy of 350,000 miles without catastrophic failure, and mechanics report it has enough durability to outlive multiple transmissions throughout the course of its life. However, there were issues with the Cummins 5.9L, such as exhaust manifold leaks and engine block cracks. Cummins continued production of its 24-valve 5.9L ISB diesel engine until 2007 when it was retired for the Cummins 6.7L diesel engine, primarily due to increased emissions regulations.

Mechanics report the Cummins 6.7L diesel engine does have some advantages over its predecessor, including more low-end torque. Depending on the model year and transmission, the 6.7L diesel engine reaches 420 horsepower and 1,075 pound-feet of torque. Its variable geometry turbocharger is more responsive (no lag) and incorporates a turbocharger brake. However, there are some disadvantages to the newer entry. The Cummins 6.7L diesel engine is much more prone to diesel particulate filter (DPF) clogging, head gasket failures and exhaust gas recirculation (EGR) system issues.

Feature comparisonCummins 6.7L diesel engineCummins 5.9L 
Production years2007 to present
2007 to current Dodge RAM 2500, 3500, 4500, 5500 trucks

2007 to 2015 Ford F-650, F-750

Various other medium-duty truck, motorhomes and school buses
5.9L 12-valve: 1989 to 1998
5.9L 24-valve ISB: 1998 to 2007
HorsepowerLow: 350 hp @ 2800 RPM
High: 420 hp @ 2800 RPM
5.9L 12-valve: 215 hp @ 2,500 RPM
5.9L 24-valve ISB: 325 hp @ 2,900 RPM
TorqueLow: 800 lb-ft @ 1700 RPM
High: 1075 lb-ft @ 1800 RPM
5.9L 12-valve: 440 lb-ft @ 1,600 RPM
5.9L 24-valve ISB: 600 lb-ft @ 1,600 RPM

Cummins 6.7L vs. Ford 6.7L Powerstroke

Ford 6.7L Powerstroke Engine Skoolie

Both the Cummins 6.7L and Ford 6.7L Power Stroke engines are still in production for consumer super-duty trucks. Mechanics report they are both highly capable and rugged engine options, and a choice may come down to truck brand loyalty.

Introduced in 2007, the Cummins 6.7L diesel engine has been installed in Dodge RAM trucks, including 2007 to present model year RAM 2500, RAM 3500, RAM 4500 and RAM 5500. It also was used to power 2007 to 2015 model year Ford F-650 and Ford F-750 Super Duty trucks, as well as other chassis cabs, medium-duty vehicles, motorhomes and school buses.

Ford Motor Company introduced the 6.7L Power Stroke diesel engine in 2011 as its all-new powerplant for Ford Super Duty trucks (F-250, F-350 and F-450), F-Series chassis cabs (F-350, F-450 and F-550), and Ford medium-duty trucks (F-650 and F-750). The Ford 6.7L is the fourth generation of the Power Stroke diesel engine family, but it is the first of those engines to be built in-house by Ford. (Ford ended a long-standing partnership with Navistar International engines due to expensive issues stemming from the previous 6.4L and 6.0L Power Stroke engines.)

Starting with a clean sheet, Ford designed the 6.7L Power Stroke diesel engine with 8-cylinders, an overhead valve (OHV), aluminum cylinder heads, cast-aluminum pistons and a compacted graphite iron block. The new metal materials offered durability, while taking weight off the overall engine (under 1,000 pounds without fluids) and contributing to better fuel efficiency.

During a decade of production, Ford continued to upgrade and refine the 6.7L diesel Power Stroke engine over three generations. Mechanics report the units made during the first generation are among the least reliable by comparison. However, Ford was able to work out the kinks in the second and third generations. 

Both the Cummins 6.7L diesel engine and Ford 6.7L Power Stroke diesel engine offer powerful versions that exceed 1,000 pound-feet of torque for heavy hauling. Mechanics report that both engines also suffer from issues related to their emissions reduction systems.

Feature comparisonCummins 6.7L diesel engineFord 6.7L Power Stroke
Production years2007 to present 2007 to current Dodge RAM 2500, 3500, 4500, 5500 trucks

2007 to 2015 Ford F-650, F-750

Various other medium-duty truck, motorhomes, and school buses
2011 to present
Ford F-Series Super Duty trucks (F-250, F-350, F-450) and Ford F-Series chassis cab 2015 – 2022
Ford F-Series medium duty trucks (F-650, F-750)
HorsepowerLow: 350 hp @ 2800 RPM
High: 420 hp @ 2800 RPM
Ford pick-up trucks
Low: 390 hp @ 2800 RPM
High: 475 hp @ 2800 RPM

Ford F-650, F-750
Low: 270 hp @ 2400 RPM
High: 330 hp @ 2600 RPM 
TorqueLow: 800 lb-ft @ 1700 RPM
High: 1075 lb-ft @ 1800 RPM
Ford pick-up trucks
Low: 735 lb-ft @ 1600 RPM
High: 1050 lb-ft @ 1800 RPM

Ford F-650, F-750
Low: 675 lb-ft @ 1600 RPM
High: 725 lb-ft @ 1800 RPM 

 

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