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Cummins ISB 6.7L Engine (Specs, Reliability & Issues)

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Last Updated on: 7th September 2023, 12:44 am

The Cummins ISB 6.7-liter straight-six turbodiesel engine is the newest and biggest generation of the B series.

Cummins’ most powerful diesel engine for light/medium-duty trucks is the ISB 6.7L (350 hp and 650 lb-ft of torque).

In this article, we’ll discuss the design of the Cummins ISB 6.7L engine, as well as its reliability and issues.

Design of the Cummins ISB 6.7L Engine

The ISB 5.9L, which preceded it, has been in production for about a decade. It was out of date at the time, and in terms of fuel consumption and pollutants, it had reached the limit of what could be improved.

The ISB 6.7 engine was created in response to a market need for a new medium-duty and bus engine.

Cummins ISB 6.7L Engine

The 6.7 ISB’s cylinder size (4.21 inches or 106.9 mm) and piston stroke were both increased (4.88 inches or 124.0 mm).

As a consequence, its displacement was increased to 6.7 litres (408 cubic inches).

The engine block is still made of cast iron. Above the block is a 24-valve cast iron cylinder head that is similar to the ISB 5.9.

The ISB6.7 cylinder head differs from the ISB5.9 cylinder head in that it has openings on the air intake plenum side (Sensor Hole Style head).

Although there are several changes from the previous generation B5.9 edition, the overall design stays the same.

A high-pressure Common Rail fuel injection system, an electronically controlled fuel injection pump, and upgraded emissions-control equipment were all included in the 6.7L Cummins engine.

In response to increasingly strict Federal emissions requirements, the new variant was designed.

In its initial year of production, the engine was the first Cummins diesel to be equipped with a diesel particulate filter (DPF).

More than 90% of soot is removed from exhaust gases by the DPF filter.

In a diesel particulate filter, a ceramic matrix filters soot particles before regenerating them at a high temperature heated by exhaust gases.

A cooling exhaust gas recirculation system was also added in the engine (EGR).

In the 2010 model year, the engine received an additional DEF (diesel exhaust fluid), SCR (selective catalytic reduction), and EGR cooler.

At lower temperatures, the DEF fluid is fed into the DPF to help with the soot regeneration process. 2 litres of DEF are needed for every 100 gallons of diesel fuel.

The Holset HE351VE variable geometry turbocharger is another exciting new element of the engine (VGT).

By obstructing exhaust flow and raising temperatures inside the DPF, this turbocharger may reduce emissions.

The VGT also comes with a built-in exhaust brake. By limiting exhaust flow, the engine is slowed. All ISB 6.7 engines come with an air-to-air intercooler as standard.

The upgrading process has never stopped in the preceding ten years of production, and the 2017 model year engines now produce up to 900 lb-ft of torque.

The smaller ISB 4.5 variation (a 4.5 litre straight four-cylinder turbodiesel engine) was built on the basis of the ISB 6.7 .

Cummins ISB 6.7L Engine Specs

  • Manufacturer: Cummins
  • Production years: 2007-current
  • Cylinder block material: Cast Iron
  • Cylinder head material: Cast Iron
  • Fuel type: Diesel
  • Fuel system: Direct injection, electronically controlled Bosch high pressure common rail injection.
  • Configuration: Inline
  • Number of cylinders: 6
  • Valves per cylinder: 4
  • Valvetrain layout: OHV
  • Bore: 4.21 inch, 106.9 mm
  • Stroke: 4.88 inch, 124 mm
  • Displacement: 408 cubic inches, 6.7 liters
  • Type: Four-stroke, turbocharged
  • Compression Ratio: 17.3 : 1
  • Power: 305-385 hp at 2,800-3,000 rpm
  • Torque: 610-900 lb-ft (827-1220 Nm) at 1,500-1,700 rpm
  • Engine weigt: 1050-1150 lbs, 476-522 kg, dry
  • Firing order: 1-5-3-6-2-4
  • Engine oil weight: SAE 15W40 diesel oil
  • Engine oil capacity: 12 qts (11.4 liters) with filter.
  • Oil change interval: 15,000 miles (24,000 km) or 6 months (7,500 miles or 6 months for 2007.5 – 2012 model years).
  • Applications: Dodge Ram pickup trucks, buses, medium duty trucks

Reliability & Issues of the Cummins ISB 6.7L

The 6.7 ISB has proved to be the most dependable Cummins B engine so far. In stock form, failure rates are minimal.

Two of the most typical difficulties are emissions equipment and Typical Rail Fuel Injection. Clogging of the EGR system is an issue that affects all engines that use EGR.

The DPF has a 100,000-kilometer life expectancy. Some owners choose to install DPF aftermarket deletion kits, which are undoubtedly less costly but also less eco-friendly.

Also keep in mind that the VGT does not tolerate long periods of inactivity.

ISB 6.7 fuel injectors need to be replaced after 200k miles. The injectors in the 6.7 version, according to owners, are more reliable than the injectors in the 5.9 version.

Updates & Changes

In 2007, the 6.7-liter engine was introduced in two versions:

  1. 350 horsepower and 650 lb-ft with a Chrysler-built six-speed 68RFE automatic gearbox
  2. 350 horsepower and 610 lb-ft with a Mercedes G56 6-speed manual gearbox

On the 2007 and later 3500 trucks, which had just 305 horsepower, the Aisin AS68RC or Mercedes G56 6-speed manual gearbox was standard.

In the 2008 4500/5500 medium duty trucks, the 350 hp and 610 lb-ft version of the engine, which comes with the Aisin AS68RC or Mercedes G56 manual, was utilised.

Since 2011, a 6.7-liter engine with 350-370 horsepower and 800 lb-ft of torque has been offered with the 68RFE automated transmission.

The Aisin AS69RC gearbox has only been available with the B6.7 engine, which generates 385 horsepower and 850-900 lb-ft of torque, since 2013.

  • Andy Lewin

    Andy Lewin is a senior mechanic, ASE qualified master technician, and an experienced automotive engineer.He's passionate about serving the automotive community with the highest-quality and trustworthy information on all things automotive. He loves to write about car repairs, maintenance, car modifications and tuning, faults, and much more.

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