Skip to content

Cummins ISB 5.9L 24v Engine (Specs, Reliability & Issues)

  • by
  • 5 min read

Last Updated on: 16th November 2023, 02:18 am

The ISB 5.9L is a straight-six turbodiesel engine from the B series of Cummins engines. The ISB engine took over from its predecessor in 1998 (the 5.9L 6BT).

The fundamental dimensions of the engine were kept, but modern technology was added to take it to the next level in terms of power, fuel economy, and environmental friendliness.

In this article, we’ll go over the design and specs of the Cummins ISB 5.9L engine, as well as its reliability and issues.


The engine block is made of cast iron. The bore size and piston stroke are identical to those of the 6BT.

Forged steel connecting rods, an assembled camshaft, and symmetrical combustion bowl aluminium pistons are all included in the ISB.

Cummins ISB 5.9 litre 24v engine

The camshaft is installed within the block. A multi-valve pushrod arrangement was used to build the ISB engine.

One of the most striking elements is the 24 valve cast iron cylinder head (but still is OHV valvetrain). Each rocker arm operates two valves.

ISB engines currently employ electronically controlled fuel systems (Robert Bosch GmbH) with a rotary type Bosch VP44 Electronic Fuel Injection Pump.

An aluminium intake manifold and a new single-piece red or silver aluminium valve cover were incorporated in the 24v engine, allowing for simpler access to the engine’s components during maintenance.

In 2003, the engine was upgraded to a Bosch high-pressure Common Rail fuel injection system, the next step in the ISB evolution.

When compared to prior Cummins engines with 24-valve engines, Common Rail injection increased power and torque while lowering engine noise.

In the 2001-2002 model year, there were two ISB Cummins engine types: one with a standard output and the other with a high output.

With the High Output ISB, only the NV5600 six-speed manual gearbox was available, which had somewhat more power (+10hp) and torque (+45 lb-ft).

The HO 5.9L Cummins had a higher compression ratio of 17.2:1, a larger flywheel, revised fuel injection timing, and a redesigned Bosch fuel system, all of which contributed to improved fuel pressure and performance.

For the 2003 model year, the high-output ISB engine developed 70 horsepower and 95 lb-ft more torque than the regular ISB engine. HO variants got 20 horsepower and 45 pound-feet of torque last year.

The HO Cummins was unavailable in California because to strict emission regulations.

The career of the 5.9 litre ISB engine came to an end in 2007. The ISB 6.7L Cummins‘ next light-duty truck engine, is more powerful and technologically advanced than the preceding B.

24v Dodge RAM ISB

The ISB engine replaced the original 6BT engine in Dodge RAM pickup trucks in the middle of 1998.

The less powerful 215 hp engine was mated with the 47RE automatic transmission until the 2003 model year, when the 47RE automatic gearbox was updated to carry increased torque capacity and renamed 48RE.

Engine Specs

  • Manufacturer: Cummins
  • Production years: 1998-2007
  • Cylinder block material: Cast Iron
  • Cylinder head material: Cast Iron
  • Fuel type: Diesel
  • Fuel system: 1998-2002; Electronically controlled Bosch VP44 rotary injection pump. 2003-2009; Bosch high pre
  • Configuration: Inline
  • Number of cylinders: 6
  • Valves per cylinder: 4
  • Valvetrain layout: OHV
  • Bore: 4.02 inch, 102 mm
  • Stroke: 4.72 inch, 119 mm
  • Displacement: 359 cubic inches, 5.9 liters
  • Type: Four-stroke, turbocharged
  • Compression Ratio: 16.3:1; 17.2:1 HO version
  • Power: 215-325 hp at 2,500 rpm
  • Torque: 420-610 lb-ft (569-827 Nm) at 1,400-1,600 rpm
  • Engine weight: 1150 lbs, 522 kg
  • 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: 7,500 miles (12,000 km) or 6 month
  • Applications: Dodge Ram pickup trucks, buses, medium duty trucks, marines

Reliability & Issues

The ISB 5.9 diesel engine has a well-deserved reputation for being a reliable, powerful, and long-lasting engine. The all-iron engine can be refurbished and has a long life expectancy.

ISB camshafts are more trustworthy because an electric fuel pump, unlike a mechanical fuel pump operated by a camshaft gear on previous B series engines, is powered by electricity.

On the other side, the electrical system left its impression. The failure rate of the electronic VP44 injection pump is higher than that of the mechanical P7100 injection pump.

Repairing the Common Rail injection is more costly, and it is more sensitive to fuel quality.

Changes & Updates

Below are the changes and updates to this engine over time.


  • Automatic transmission: 215 hp at 2,700 rpm, 420 lb-ft at 1,600 rpm.
  • Manual transmission: 235 hp at 2,700 rpm, 460 lb-ft at 1,600 rpm.


  • Standard version for manual and automatic transmission: 235 hp at 2,700 rpm, 460 lb-ft at 1,400 rpm.
  • High-output version with manual transmission: 245 hp at 2,700 rpm, 505 lb-ft at 1,600 rpm.


  • Standard version for manual and automatic transmission: 235 hp at 2,700 rpm, 460 lb-ft at 1,400 rpm.
  • High-output version with manual transmission: 305 hp at 2,900 rpm, 555 lb-ft at 1,600 rpm.


  • Standard version for manual and automatic transmission: 305 hp at 2,900 rpm, 555 lb-ft at 1,400 rpm.
  • High-output version with manual transmission: 325 hp at 2,900 rpm, 610 lb-ft at 1,400 rpm.
  • Cars offered in CA: 235 hp at 2,700 rpm, 460 lb-ft at 1,400 rpm.


  • Single version produced 325 hp at 2,900 rpm, 610 lb-ft at 1,600 rpm.
  • 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.

Share this article
Available for Amazon Prime