Cummins B6.7 (ISB)
6.70L Inline-6 turbo diesel • Cummins
About the Cummins B6.7 (ISB)
The Cummins B6.7 (formerly ISB6.7 and before that ISB) is a 6.7-liter inline-6 turbo diesel — the smallest Cummins commercial engine. It's used in two distinct markets: (1) Class 6-7 medium-duty conventional trucks (Freightliner M2 106, International MV, Hino L-Series), and (2) Class 3-5 pickup chassis trucks (Dodge/Ram 2500, 3500, 4500, 5500 — where it's marketed as 'Cummins 6.7L Turbo Diesel'). The B6.7 has been continuously updated since 1998 (original B5.9 ISB), with displacement growing from 5.9L to 6.7L in 2007 to meet EPA emissions requirements. The Cummins B6.7 is the most widely used Cummins engine globally and a strong contributor to Cummins' parts and service revenue.
Overview
The Cummins B6.7 (formerly ISB6.7 and before that ISB) is a 6.7-liter inline-6 turbo diesel — the smallest Cummins commercial engine. It's used in two distinct markets: (1) Class 6-7 medium-duty conventional trucks (Freightliner M2 106, International MV, Hino L-Series), and (2) Class 3-5 pickup chassis trucks (Dodge/Ram 2500, 3500, 4500, 5500 — where it's marketed as 'Cummins 6.7L Turbo Diesel'). The B6.7 has been continuously updated since 1998 (original B5.9 ISB), with displacement growing from 5.9L to 6.7L in 2007 to meet EPA emissions requirements. The Cummins B6.7 is the most widely used Cummins engine globally and a strong contributor to Cummins' parts and service revenue.
Specifications
- Manufacturer
- Cummins
- Displacement
- 6.70 liters
- Configuration
- Inline-6 turbo diesel
- Fuel type
- Diesel
- Horsepower
- 200–360 hp
- Torque
- 520–800 lb-ft
- Production years
- 2007–present
- Truck classes
- Class 6-7, Class 3-5 (RAM)
- Applications
- Medium-duty conventional, RAM Heavy Duty pickup
Design and engineering
6.7L inline-6 with cast iron block (parent bore — not wet sleeve like the X15). Variable geometry turbocharger. High-pressure common rail. EPA-compliant aftertreatment varies by application — RAM trucks use a slightly different DEF/SCR configuration than medium-duty trucks.
Generations and emissions eras
Reliability and longevity
Pre-2007 ISB 5.9L is considered legendary for reliability — many examples have crossed 700K-1M miles with original head and bottom-end. 2007-2010 ISB 6.7L was less reliable due to EGR-heavy emissions. 2013+ SCR-equipped ISB/B6.7 is solid. RAM truck applications generally see lower mileage than commercial medium-duty applications, so RAM Cummins engines often outlive the truck itself.
Common problems
Pre-2007 ISB 5.9L: lift pump failures (eats injectors if undetected), fuel #47 connector issues. 2007-2010 6.7L: EGR cooler failures, turbo failures, DPF issues. 2013+ ISB/B6.7: DEF system, NOx sensors, injector cup wear on certain production runs.
Maintenance schedule
Engine oil every 15,000-20,000 miles (pickup, lighter load). Engine oil every 30,000-40,000 miles (commercial medium-duty). Fuel filter every 15,000-20,000 miles. DEF tank refill every 4,000-7,000 miles depending on load.
Pros and cons
✓ Pros
- • Massive parts availability and service network
- • Pre-2007 5.9L is legendary for reliability
- • Inline-6 vs V8 competitors (better fuel efficiency, simpler maintenance)
- • Multiple market applications (pickup AND commercial)
- • Widely understood by mechanics worldwide
⚠ Cons
- • 2007-2010 EGR-era engines are problematic
- • Parent-bore block — can't in-frame rebuild like X15/L9
- • DEF system maintenance burden
Resale value impact
RAM trucks with Cummins 6.7L hold value significantly better than competing Ford Power Stroke or GM Duramax trucks — typically $5,000-10,000 premium at 3-5 years old. Pre-2007 RAM Cummins trucks sell for prices that defy normal depreciation curves due to enthusiast demand.