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Cummins ISM-425 Specifications
| Engine Model: Cummins ISM-425 |
| Engine Type: 4-cycle inline 6-cylinder HPCR or Celect fuel injection liquid-cooled diesel |
| Total Displacement: 661 cu.in (10.8 L) |
| Rated Engine Power: 425 Hp (317 kW) at 2000 rpm |
| Aspiration Type: Turbocharged |
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| General Technical Data |
The Cummins ISM-425 is a high-output, electronically controlled, turbocharged and aftercooled inline six-cylinder diesel engine designed for heavy-duty on-highway trucks, vocational machinery, buses, and industrial equipment. As part of the Cummins ISM/ISM11 engine platform, the ISM-425 represents a powerful upper-range calibration delivering 425 horsepower and strong low-end torque suitable for long-haul trucking, regional haul, heavy vocational work, and off-road industrial cycles.
Equipped with advanced ECM logic, high-pressure
electronic fuel injection, robust cast-iron architecture, and optimized
combustion systems, the ISM-425 delivers durable performance, improved
fuel efficiency, and reliable operation under severe-duty conditions.
The engine is known for long service intervals, wide parts availability,
ease of service, and emissions compliance capabilities depending on
market configuration.
The ISM-425 is a four-stroke, inline six-cylinder diesel engine with a
displacement of approximately 10.8 liters (659 cubic inches). Bore
typically measures 125 mm (4.92 inches) and stroke measures 147 mm (5.79
inches), giving the engine a long-stroke design optimized for high
torque production. Compression ratio varies with emission calibration
but generally ranges from 16.5:1 to 17.0:1. Rated power output is
approximately 425 horsepower (317 kW) at around 1800–2100 rpm.
Peak torque ranges from 1650 to 1850 Nm
(1217–1365 lb-ft) typically delivered around 1100–1400 rpm. Idle speed
is normally set at 650–700 rpm. Firing order is 1–5–3–6–2–4.
Turbocharging and charge-air cooling ensure efficient combustion,
improve altitude performance, and provide strong acceleration under
heavy loads. Electronic control optimizes fuel delivery, boost levels,
emissions functions, and protection strategies across operating
conditions.
The cylinder block is made from heavy-duty cast iron designed to
withstand high internal pressures. Reinforcing ribs increase rigidity
and reduce flex under severe loads. The forged-steel crankshaft is
supported by seven large main bearings engineered to reduce torsional
vibration and deliver long service life. Wet or replaceable liners
(varies by version) improve cooling and simplify overhaul.
Machined oil galleries supply lubricating oil
to crankshaft bearings, connecting rods, and camshaft bearings. Cast-in
coolant jackets support uniform heat distribution, reducing the risk of
localized overheating. Integrated piston cooling nozzles spray oil
beneath piston crowns to manage thermal load. Threaded mounting bosses
provide accommodation for alternators, PTO units, hydraulic pumps, and
other accessories used in vocational vehicles and industrial equipment.
The cast-iron cylinder head features direct-injection combustion
chambers optimized for high-pressure electronic injection. Each cylinder
includes four valves–two intake and two exhaust–to enhance airflow and
support clean, efficient combustion. Valve actuation is managed by
rocker arms and pushrods actuated by a camshaft mounted in the block.
Hardened valve seats and heat-resistant guides withstand extreme thermal
cycling.
Hydraulic lash adjusters may be included depending on configuration, reducing service intervals. Coolant passages integrated into the head stabilize the thermal profile and prevent distortion or gasket failure. A multi-layer steel head gasket maintains sealing integrity under elevated peak firing pressures associated with high-power calibrations.
| Fuel System |
Depending on production year, the ISM-425 utilizes Cummins Celect, Celect Plus, or High-Pressure Common Rail (HPCR) fuel systems. A lift pump draws fuel from the tank through primary and secondary filters. The high-pressure pump delivers fuel to electronically actuated injectors at pressures typically exceeding 1400–1600 bar (20,300–23,200 psi). Multiple injection events–pilot, main, and post injection–enhance torque delivery, reduce particulate formation, minimize combustion noise, and improve cold-start characteristics.
The ECM continuously monitors crankshaft and camshaft position, rail pressure, boost pressure, intake manifold temperature, EGR activity (if equipped), fuel temperature, and exhaust temperatures. Injection timing, fuel quantity, and pressure are dynamically adjusted for optimal performance and emissions compliance. High-efficiency filters protect injectors from contamination.
| Lubrication System |
The ISM-425 has a full-pressure wet-sump lubrication system powered by a gear-driven pump. Oil is drawn through a pickup strainer, passed through a full-flow filter, and distributed to the main oil gallery. Pressurized oil lubricates crankshaft bearings, connecting rod bearings, camshaft bearings, rocker assemblies, and turbocharger bearings. Piston cooling jets regulate piston crown temperature during high-load operation.
Typical operating oil pressure ranges from 300 to 500 kPa (44–72 psi). Idle pressure is usually between 100 and 150 kPa (15–22 psi). Oil capacity typically ranges from 27 to 33 liters (28.5–34.8 US quarts). Low-ash oil are required for engines equipped with DPF/SCR aftertreatment systems to protect catalyst surfaces and ensure long component life.
| Cooling System |
The cooling system uses a belt-driven centrifugal water pump to circulate coolant through block and head passages. The thermostat begins opening at approximately 82°C (180°F) and is fully open around 95°C (203°F). System pressure generally ranges from 90 to 110 kPa (13–16 psi). Coolant capacity varies with installation but typically ranges from 35 to 55 liters (37–58 US quarts).
Charge-air cooling (air-to-air or air-to-water) reduces intake temperature, enhances torque stability, and supports emissions compliance. Proper coolant chemistry protects against corrosion, scale, and cavitation. The ECM monitors coolant temperature and activates derate or shutdown strategies during over-temperature events.
| Other Systems |
Turbocharging on many ISM-425 variants uses a variable-geometry turbocharger (VGT), enhancing boost response, emissions control, altitude compensation, and engine-braking capability. Wastegated turbochargers may be used depending on calibration. Air filtration uses heavy-duty dry-element filters with optional dual-stage filtration for dusty environments. Exhaust systems may include EGR valves, DOC, DPF, SCR, and ammonia slip catalysts depending on emissions tier.
Electrical systems operate on 12- or 24-volt circuits, using alternators rated between 80 and 150 amperes. ECM diagnostics include fault-code storage, derate logic, overspeed protection, coolant-loss detection, and turbo overspeed control. Accessory drives support PTO units, pumps, and industrial powering equipment.
| Dimensions and Weight |
Length: 1350–1550 mm (53.1–61.0 in)
Width: 800–950 mm (31.5–37.4 in)
Height: 1150–1450 mm (45.3–57.1 in)
Dry weight generally ranges from 900 to 1150 kg (1984–2535 lb),
depending on emissions equipment, turbocharger configuration, and
accessory layout.
| Maintenance Data |
Oil and filter changes: every 500 hours or according to manufacturer
mileage recommendations.
Fuel filters: replace every 400–500 hours; drain water separators
routinely.
Air filters: replace every 200–400 hours depending on dust exposure.
Coolant: replace every two years or as coolant chemistry requires.
Valve lash: inspect on non-hydraulic-adjuster models.
Aftertreatment: DPF cleaning, SCR inspection, and regeneration as
required.
ECM diagnostics: use logged codes to support predictive maintenance.
| Tightening Torques |
Cylinder head bolts: 220–260 Nm (162–192 lb-ft)
Main bearing caps: 180–220 Nm (133–162 lb-ft)
Connecting rod bolts: 90–120 Nm (66–89 lb-ft)
Flywheel bolts: 300–350 Nm (221–258 lb-ft)
Crankshaft pulley bolt: 280–320 Nm (207–236 lb-ft)
Injector hold-down: 25–30 Nm (18–22 lb-ft)
Intake heater/glow plug: 10–15 Nm (7–11 lb-ft)
Oil drain plug: 40–50 Nm (30–37 lb-ft).
| Vehicle Applications |
The Cummins ISM-425 powers long-haul trucks, regional-haul tractors, vocational dump trucks, refuse vehicles, fire engines, concrete mixers, transit buses, agricultural equipment, construction machinery, cranes, industrial pumps, compressors, and generator systems. Its torque capability, durability, and emissions compatibility make it suitable for diverse heavy-duty service environments.
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