6.7 Cummins Turbodiesel

The Cummins 6.7 liter ISB is an inline six cylinder diesel engine employed in a diverse pool of vehicles and equipment, including the series of Ram pickup and chassis cab trucks. Ram Trucks (formerly the Dodge truck brand) adopted the 6.7 Cummins during the 2007 model year while simultaneously phasing out Cummins' 5.9 liter turbodiesel engines.

PACCAR began offering the 6.7 Cummins in its 2008 model year medium duty trucks under both the Peterbilt and Freightliner brands. Ford Motor Company offered the 6.7 liter Cummins turbodiesel in 2007 to 2015 model year F-650 and F-750 medium duty trucks. International has offered the 6.7 liter in various medium duty truck models since 2014. It is also a common engine in various school bus and motorhome applications. It has a sister engine that is designated for off-highway applications, including equipment commonly found in the construction, commercial, marine, and agricultural markets.

Replacement of the 5.9 liter ISB turbodiesel engine was necessitated by more stringent emissions standard in the United States. Additionally, and particularly relevant to its usage in Ram Trucks, the engine has served as a competitive platform with ample room for future growth in the fiercely competitive diesel truck segment. Note that the majority of the information available on this page holds an obvious emphasis on the engine variants used in Ram 2500, 3500, 4500, and 5500 truck models.

Engine Features

The 6.7 liter Cummins' design is characterized by its I-6 cylinder arrangement and undersquare bore-stroke ratio. An undersquare bore-stroke ratio, where the cylinder bore diameter is less than the length of the piston stroke, is a common feature of heavy duty inline engines and tends to naturally result in an engine that produces excellent low-end torque and good low to mid-range power. Such characteristics are well suited for towing and translate favorably when bringing a heavy trailer up to speed or hauling steep grades.

Cummins originally designed the 6.7 liter with a grey cast iron engine block, but switched materials and manufactured the engine blocks from CGI beginning in 2019. Following the 2024 model year production engines, Cummins would revert back to grey cast iron. Evidence suggests that the original switch to CGI was primarily to reduce weight (the engine shed approximately 60 lbs), but grey cast iron provided superior bottom-end rigidity and NVH isolation.

Fuel System

All 6.7 Cummins turbodiesel engines employ a high pressure common rail injection system. From 2007 to 2018 the Bosch CP3 injection pump (HPFP) was used. Cummins then adopted the Bosch CP4.2 injection pump for 2019, only to retire it and revert back to the CP3 pump beginning in 2021. For 2025, the 6.7 Cummins relies on a Bosch CP8 injection pump; little information is currently know about the new HPFP but it is expected to be considerably more robust.

Late in 2021, FCA and Cummins issued a voluntary recall of all 2019 and 2020 model year Ram trucks, retrofitting the engines with CP3 pumps. The Bosch CP4 injection pump has been the source of great controversy in GM and Ford trucks as its reliability has been called into question and is the source of multiple lawsuits seeking compensation for affected vehicle owners under the assumption that manufacturers were aware of the fact that diesel fuel in the United States lacked the minimum lubricity requirements required by the pump.

Turbocharger

Air is fed to the 6.7 Cummins via a Holset variable geometry turbocharger. 2007 to 2012 engines employed a model HE351VE turbocharger while later engines featured the Holset HE300VG. In both turbochargers, the VGT vanes are electronically controlled and actuated. All Dodge/Ram trucks also utilize a charge-air-cooler (intercooler) to reduce the temperature and increase the density of the intake air charge.

Starting Aids

Like its predecessors, the 6.7 Cummins used a grid heater (also heater grid, intake heater) as a cold starting aid for 2007 to 2024 model engines before introducing a glow plug system for 2025. The grid heater is a resistive heating element comprised of a matrix of thin conductors. It is mounted in the upper pathway of the intake manifold such that the intake air charge must pass through the device before entering any cylinder's combustion chamber.

When cycled on during the wait-to-start period, the heating element draws a relatively large current form the vehicle batteries (on the realm of 200 amps, give-or-take) that rapidly heats the conductor matrix. When the engine is cranked, the cold intake air charge passes through the grid heater, increasing its temperature before it is distributed to each combustion chamber.

Under the correct conditions, the grid heater is also used to raise intake air temps for a brief period after start-up. Doing so contributes to more complete combustion for reduced emissions and a lower propensity of cylinder washing, a contributor to fuel dilution, on a cold soaked engine. The transition to glow plugs for the 2025 model engines effectively moves the heating elements inside the actual combustion chamber for more efficient heat transfer and reduced emissions on start-up. Some Ram dealer data for 2025 suggests that the glow plug system reduces engine start time, but this is largely debatable and would depend on a number of variables.

Emission Control Technologies

All 6.7 Cummins turbodiesels employ a diesel oxidation catalyst and diesel particulate filter. In fact, a major factor in the transition from the 5.9 liter to the 6.7 liter in the 2007 model year was to conform with more stringent Federal emissions regulations that required a diesel particulate filter. For 2007 to 2010 chassis cabs and 2007 to 2012 pickup trucks, a NOx absorption catalyst was also included as part of the exhaust aftertreatment system. Chassis cab trucks adopted SCR in 2011 and pickup trucks began using it in 2013.

SCR requires that DEF, a urea based solution, be perpetually injected into the exhaust stream to reduce tailpipe emissions of nitrous oxides. The engines also employ a cooled exhaust gas recirculation system. A small portion of exhaust gases are cooled and returned to the combustion chamber as a method of displacing oxygen and thus cooling the combustion temperature, which reduces the formation of nitrous oxides during the combustion event.

Available Transmissions

In Ram truck applications, the 6.7 liter Cummins has been available mated to a total of five transmissions:

• The Chrysler 68RFE six speed automatic in 2007 to 2024 pickup trucks
• The Mercedes G56 six speed manual transmission in 2007 to 2018 pickup and chassis cab trucks
• The Aisin AS68RC six speed automatic in 2007 to 2012 chassis cab trucks
• The Aisin AS69RC six speed automatic in 2013 to 2024 Ram 3500 pickup and all chassis cab trucks
• The ZF PowerLine eight speed automatic transmission introduced for the 2025 model year in pickup and chassis cab trucks

Ram retired the AS68RC transmission in chassis cab trucks and replaced it with the AS69RC for 2013, the same year that they introduced a High Output variant of the 6.7 Cummins that was only available in Ram 3500 models and utilized the same transmission. The 68RFE, which has no PTO provisions, was never available in chassis cab trucks.

The G56 manual transmission was offered through the 2018 model year and did not return for 2019. Trucks equipped with the G56 required a significantly de-rated engine calibration, thus the Cummins' horsepower and torque growth through the years was not realized in manual transmission equipped trucks. In 2018, for example, trucks with the G56 gearbox were rated at a peak 660 lb-ft of torque to the 800 lb-ft produced by 68RFE trucks and the whopping 930 lb-ft that H.O. engines mated to the AS69RC were rated at.

For 2025, Ram introduced the ZF built PowerLine 8 eight speed automatic transmission. The transmission is standard on all pickup and chassis cab trucks and there are no alternative offerings, simplifying the powertrain structure between models. Ram also standardized the H.O. engine for 2500 models and there is no longer a standard output engine available.

6.7 Cummins Chronology of Changes

The diesel segment has grown increasingly competitive, and Cummins has ensured that the 6.7 Turbodiesel has evolved accordingly. Many of the engine's changes through time were necessitated by significant increases in its performance, requiring structural improvements to support greater stresses. Other changes represent cleaner emissions, improved fuel economy, greater reliability, or even a combination of all these factors. The most comprehensive engine changes occurred for the 2013, 2019, and 2025 model years.

2009

• Access port integrated into the turbocharger turbine housing to permit cleaning of the VGT vanes without removing the turbocharger from the engine; increased serviceability
• Updated fuel filter housing, fuel filter element with improved filtration
• Revised water pump inlet housing design
• Revised exhaust gas recirculation coolant hoses and fittings

2010

• Transitioned to a single, engine mounted ECU (PCM) that controls engine and transmission functions; previous engines employed separate, standalone units for the engine and transmission
• Revised fuel filter housing, added a quarter turn drain valve to the side of the housing
• Revised thermostat with a slightly higher 200 °F opening temperature, providing a marginal increase in designed engine operating temperature; new thermostat not interchangeable with earlier engines

2011

2011 model year pickup trucks with the 68RFE automatic transmission received a substantial 150 lb-ft increase in peak torque. Power ratings remained the same in all applications, and G56 equipped trucks did not see any changes in engine performance for 2011. Selective catalytic reduction was added to the exhaust aftertreatment system of chassis cab trucks for 2011, requiring the use of DEF.

2013

The 2013 model year saw horsepower and torque increases across the board. Chassis cab trucks with the G56 manual transmission gained 15 horsepower and 40 lb-ft while automatic trucks saw an increase of 20 horsepower and 140 lb-ft of torque. Pickup trucks with the G56 gained 50 lb-ft of torque, although horsepower remained the same. Standard output engines gained 20 horsepower, but carried over the 800 lb-ft torque figure from the previous model year. A High Output variant of the 6.7 Cummins is introduced for Ram 3500 models (single and dual rear wheel) and is rated with 15 more horsepower and 50 lb-ft of torque more than the standard output engine.

• Selective catalytic reduction becomes standard on all 6.7 Cummins equipped pickup trucks, requiring the use of DEF
• New camshaft design introduced for chassis cab trucks only; revised intake duration and lift
• New piston design
  • Coating added to skirt area to reduce wear on cylinder walls, dampen piston slap during cold start
  • Piston bowl was redesigned for reduced exhaust emissions
  • New piston cooling jet design
• New vibration damper, addressing the demands of the more powerful engine lineup
• Revised bed-plate
• New Holset model HE300VG turbocharger
• New ECU with two 96 pin connectors (versus prior two 76 pin connectors) providing additional data input processing for the SCR system
• New, larger EGR cooler
• Reduced water pump/fan drive pulley diameter to increase their rotational speeds at a given engine RPM
• AS68RC transmission no longer available in chassis cab trucks, replaced by AS69RC

2016

High Output engines receive a new calibration that adds 35 lb-ft of torque, brining total output on the H.O. 6.7 Cummins to 900 lb-ft. There are no output adjustments to standard production engines nor any powertrain configuration offered in chassis cab trucks.

2018

Torque on High Output engines is increased from 900 to 930 lb-ft of torque via a new engine calibration. There are once again no changes for standard output engines or chassis cab trucks. 2018 marks the final year that the G56 manual transmission is offered in a Ram Truck.

2019

Cummins provided torque improvements across the board for pickup truck engines. Torque is increased from 930 to 1,000 lb-ft for H.O. engines and from 800 to 850 lb-ft for the standard output option. Power is also increased, from 385 to 400 horsepower, in H.O. engines. The 6.7 Cummins becomes the first pickup truck engine to reach the 1,000 lb-ft mark. There is no change in the output of engines in chassis cab trucks and their calibration is carried over from the prior model year.

• New piston design with a larger connecting rod pin bore (accepts larger wrist pin), slightly altered bowl geometry for improved swirl, low friction piston rings; compression ratio decreased to 16.2 to 1 for high output engines and increased to 19.0 to 1 for standard output engines.
• New high strength forged connecting rods
• New high strength crankshaft
• New deep skirt engine block cast from compacted graphite iron (previously grey cast iron); reduced weight, significant improvements in strength and rigidity
• Revised cylinder head design with new springs, exhaust valves, and rocker arms; cylinder head bolt diameter increased
• Hollow camshaft design adopted for reduced weight, camshaft profile revised
• Maintenance-free hydraulic lifters replace prior solid lifter design; no adjustment necessary, reduced engine noise
• Revised rocker arms
• Revised Holset turbocharger calibrated to provide up to 33 psig of manifold pressure
• Exhaust manifold revised with elongated mounting holes to prevent cracks resulting from thermal expansion, turbocharger mounting position moved to between cylinder 4 and 5 exhaust manifold runners (previously located centrally between cylinders 3 and 4)
• Bosch CP4.2 fuel injection pump replaces long-running CP3 unit, maximum injection pressure increased from 26,000 to 29,000 psi
• Revised fuel injectors
• Increased cooling system capacity
• High volume lube oil pump
• Water and oil pumps redesigned into aluminum housings (previously cast iron)

2020

A new engine calibration for chassis cab trucks increases power from 325 to 360 horsepower (+35) and torque from 750 to 800 lb-ft (+50). There are no changes for pickup truck engines.

2021

For 2021, the 6.7 Cummins reverted back to a Bosch CP3 injection pump, ditching the controversial CP4 pump. Additionally, a recall is opened on all 2019 and 2020 model year vehicles employing the CP4 injection pump to have them retrofitted to the CP3. High Output engines see a 75 lb-ft and 20 horsepower increase in torque and power via a new ECU calibration. Power and torque for standard output engines is unchanged, as is that for chassis cab trucks.

2025

Ram introduced a simplified powertrain structure for the 2025 model year, offering a single diesel option in all Ram chassis cab and pickup trucks; the High Output 6.7 Cummins mated to the ZF PowerLine 8 (TorqueFlite HD 8) eight speed automatic transmission. Although all applications employ the same engine, note that chassis cab trucks continue to operate on an alternative ECU calibration at lower power and torque levels than pickup truck engines, which gained an additional 10 horsepower for the 2025 model year.

• Bosch CP8 fuel injection pump capable of 39,000 psi replaces CP3 pump
• Traditional glow plug system replaces the grid heater; primarily benefit is believed to be reduced emissions at engine start-up
• New cartridge style engine oil filter; replaces spin-on type filter
• Revised turbocharger
• Engine mounted DOC; improved DOC efficiency and "light-off" by moving it closer to the engine
• "7th injector" regeneration strategy adopted, used to "light-off" DOC upon startup for reduced emissions
• Revised exhaust gas recirculation system
• New cylinder head design with externally mounted fuel injectors for improved serviceability
• New intake manifold with optimized flow path for improved cylinder distribution
• New grey cast iron engine block (no longer CGI)
• New piston design, compression ratio lowered to 16.0 to 1
• ZF PowerLine 8 transmission becomes standard on all models

Engine Specs

[1] - Standard output engine.
[2] - High output engine.
[3] - Chassis cab trucks only.
[4] - Cold engine, minimum 0.006 in., maximum 0.015 in.; adjustment is required if the intake valve lash is not within these limits. No adjustment necessary on 2019 and newer engines with maintenance-free hydraulic lifters.
[5] - Cold engine, minimum 0.021 in., maximum 0.034 in.; adjustment is required if the exhaust valve lash is not within these limits. No adjustment necessary on 2019 and newer engines with maintenance-free hydraulic lifters.
[6] - Ram pickup and chassis cab trucks; alternative applications may have a system capacity greater than 12 quarts, always verify fluid capacities in the vehicle's owner manual.
[7] - Do not exceed manufacturer recommended biodiesel limits, significant fuel contamination and/or fuel system corrosion probable.
[8] - Ram pickup and chassis cab trucks only.

Horsepower & Torque Ratings

Pickup Trucks

[9] - Beginning with trucks built February 2011; some early builds received 2010 engines.
[10] - Standard with High Output engine, Ram 3500 models only.
[11] - Engine and transmission options consolidated for 2025 model year, High Output Cummins and ZF 8 speed transmission became standard on all 2500/3500 models equipped with diesel engine option.

Chassis Cab Trucks

[12] - Transmission options consolidated for 2020 model year, only automatic transmission available. AS69RC used 2020 through 2024, ZF 8AP1075 used 2025 onward.

Medium Duty Trucks

Ford Motor Company offered the 6.7 Cummins as an engine option in F-650 and F-750 medium duty truck models beginning the 2007 model year and ending the 2015 model year. During this period, the 6.7 Cummins was offered in the following horsepower and torque rating combinations:

Horsepower & Torque Curves

Ram/Cummins Recall CP4 Injection Pump

The 6.7 Cummins employed the tried-and-true Bosch CP3 injection pump through the 2018 model year. For 2019, Cummins adopted the Bosch CP4 injection pump, presumably due to its "higher efficiency". However, the Bosch CP4, which GM used in the 6.6 Duramax from 2011 to 2016 and Ford has used since 2011 in the 6.7 Power Stroke, has been the source or major reliability concerns and total fuel system failures. There is much speculation as to what causes the Bosch CP4 "failure event", but the general consensus is that ULSD fuels used in the United States lack the lubricity necessary to keep the roller followers from wearing.

The inevitable failure event flushes metal debris throughout the entire fuel system, typically requiring replacement of the fuel injectors, fuel lines, fuel pump, injection pump and necessitating a deep cleaning of the fuel tank and other associated parts. Repairs can cost in excess of $10,000 and are generally not covered under warranty because OE's classify such a failure as "contamination" of the fuel system.

As of 2021 several, if not dozens of lawsuits were pending across the U.S. seeking damages for affected GM, Ford, and Ram truck owners. Due to these reliability issues and the growing number of complaints with the CP4 injection pump, Cummins began using the Bosch CP3 injection pump again for the 2021 model year. Additionally, FCA voluntarily recalled all Cummins equipped Ram trucks employing the Bosch CP4 injection pump late in 2021 (NHTSA recall number 21V-88). Additional information on this recall and Bosch CP4 failures can be found here: Bosch CP4 failure information.

Fuel Dilution Problems in Early 6.7 Cummins Diesels

Fuel dilution of the engine oil became a problem as the result of how the 6.7 Cummins handled regeneration cycles. Specifically, the 6.7 Cummins relies on a post-injection technique to raise the exhaust system and DPF temperatures during active regeneration, which cleans the DPF by burning off particulate matter that has accumulated in the DPF substrate. During a post-injection event, fuel is injected into the combustion chamber during the exhaust stroke. The fuel therefore does not burn in the combustion chamber, but rather is sent into the exhaust system as an atomized mixture.

Because raw fuel is injected, but not burned in the cylinder during this process, cylinder washing and fuel dilution can occur at relatively high rates and it was not uncommon for owners to see fuel dilution in excess of 5% between oil change intervals. When SCR was employed on the 6.7 Cummins, these rates dropped significantly and later trucks are much less prone to fuel dilution problems than the 2007 to 2012 model year pickups and 2007 to 2010 model year chassis cabs.

Author - T. List
Editor, Diesel Hub