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Cummins ISX12 Specifications
| Engine Model: Cummins ISX12 |
| Engine Type: 4-cycle inline 6-cylinder Extreme Pressure Injection liquid-cooled diesel |
| Total Displacement: 726 cu.in (11.9 L) |
| Rated Engine Power: 345-500 Hp (257-373 kW) at 2100 rpm |
| Aspiration Type: Turbocharged and aftercooled |
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| General Technical Data |
The Cummins ISX12 is a modern, electronically controlled, turbocharged and aftercooled inline six-cylinder diesel engine designed for heavy-duty on-highway trucks, regional-haul tractors, vocational trucks, buses, and industrial machinery. As part of the Cummins ISX product family, the ISX12 bridges the gap between mid-range and large-bore platforms, delivering a strong power-to-weight ratio, fuel-efficient performance, and emissions compliance for EPA10, Euro V, and selected Euro VI/China VI markets depending on configuration.
Featuring an advanced XPI (Extreme Pressure
Injection) fuel system, cooled EGR (where required), robust electronic
controls, and optimized combustion architecture, the ISX12 provides high
torque density, low operating cost, and durable long-term service
capability. It is known for its responsive acceleration, reliable power
delivery, simplified service access, and strong compatibility with a
wide variety of heavy truck chassis.
The Cummins ISX12 is a four-stroke, inline six-cylinder diesel engine
with a displacement of approximately 11.9 liters (726 cubic inches).
Bore typically measures 130 mm (5.12 inches), while stroke is
approximately 150 mm (5.91 inches), forming a long-stroke configuration
designed to produce high torque at mid- and low-range engine speeds.
Compression ratio varies depending on emissions tier and calibration,
but commonly falls between 16.5:1 and 17.0:1.
Power output generally ranges from 257 to 373
kW (345–500 horsepower) at approximately 1800–2100 rpm. Peak torque
typically ranges from 1650 to 2250 Nm (1217–1659 lb-ft), normally
available between 1100 and 1400 rpm. Idle speed is usually set between
600 and 650 rpm. The firing order is 1–5–3–6–2–4. Air-handling is
managed by a variable-geometry turbocharger in most variants, providing
superior transient response, optimal boost control, and improved
emissions compliance.
The cylinder block is cast from high-strength compacted graphite iron
(CGI) or heavy-duty gray iron depending on version. The block
incorporates deep reinforcement ribs to improve stiffness and reduce
vibration. The forged-steel crankshaft is supported by seven main
bearings designed to handle high cylinder pressures associated with
modern emissions-compliant heavy-duty diesel operation. Wet cylinder
liners provide consistent cooling and ease of overhaul, while machined
oil galleries supply pressurized lubrication to critical areas.
Coolant jackets are cast into the block to
allow for even thermal distribution and minimal localized hot spots.
Piston cooling jets direct oil to the underside of the piston crowns to
manage thermal load and improve piston durability in high-duty cycles.
Accessory mounting pads support alternators, PTO systems, refrigerant
compressors, hydraulic pumps, and other vocational equipment.
The cast-iron cylinder head incorporates direct-injection combustion
chambers optimized for XPI high-pressure injection. Each cylinder uses
four valves–two intake and two exhaust–to improve airflow, combustion
efficiency, torque, and fuel economy. Valves are actuated by rocker arms
and pushrods connected to a camshaft mounted in the block. Exhaust
valves are built with high-temperature alloys, and hardened valve seats
maintain sealing integrity under high thermal cycling.
Integrated coolant passages stabilize head temperature, reducing risk of warping or gasket failure. Combustion chamber geometry maximizes swirl and atomization, improving emissions performance and cold-start behavior. Depending on model year and configuration, hydraulic lash adjusters may be included to reduce maintenance requirements.
| Fuel System |
The ISX12 uses the Cummins XPI (Extreme Pressure Injection) fuel system. Fuel is drawn from the tank through a lift pump and series filtration stages, including primary water-separating and secondary high-efficiency filters. The high-pressure pump delivers fuel at pressures exceeding 2000 bar (29,000 psi). Electronically actuated injectors deliver multiple injection events for each combustion cycle, including pilot, main, and post injections that improve efficiency, reduce combustion noise, and assist emissions reduction.
The ECM monitors crankshaft and camshaft position, rail pressure, boost pressure, fuel temperature, coolant temperature, intake pressure, exhaust aftertreatment sensors, and EGR flow where applicable. Injection timing, duration, and quantity are continuously adjusted to optimize power output and emissions compliance.
| Lubrication System |
The lubrication system is a full-pressure wet-sump configuration powered by a gear-driven pump. Oil is drawn through a pickup screen in the sump and directed through a full-flow filter before entering the main oil gallery. Pressurized oil lubricates crankshaft bearings, connecting-rod journals, camshaft bearings, rocker arms, and turbocharger bearings. Piston cooling jets manage crown temperature under high load.
Typical operating oil pressure ranges from 300 to 500 kPa (44–72 psi). Idle oil pressure generally falls between 100 and 150 kPa (15–22 psi). Oil capacity varies with sump configuration but typically ranges from 28 to 38 liters (29.6–40.1 US quarts). Low-ash oil are required for DPF/SCR-equipped variants to ensure aftertreatment durability.
| 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 near 95°C (203°F). System pressure ranges from 90 to 110 kPa (13–16 psi). Coolant capacity varies by installation but generally ranges between 40 and 55 liters (42.2–58.1 US quarts).
Charge-air cooling–either air-to-air or air-to-water–reduces intake temperature, improving torque output and lowering NOx formation. Coolant chemistry must be carefully maintained to prevent corrosion, cavitation, and precipitation that may affect water pump seals and cylinder liner longevity. The ECM monitors coolant temperature and triggers derate or shutdown strategies in overheating conditions.
| Other Systems |
The turbocharging system on most ISX12 variants uses a variable-geometry turbocharger (VGT) to optimize boost across the rpm range. VGT improves transient response, enhances torque, supports EGR function where equipped, and improves engine braking performance. Intake systems feature heavy-duty dry-element filters with optional two-stage filtration for dusty environments. The exhaust system may include DOC, DPF, SCR, ammonia slip catalysts, and EGR valves depending on emissions tier.
Electrical systems operate on 12- or 24-volt configurations, with alternator output ranging from 80 to 150 amperes. ECM diagnostics, derate strategies, fault detection, and real-time monitoring support reliability and ease of troubleshooting. PTO provisions, hydraulic pump mounts, and auxiliary drive pulley options increase installation versatility.
| Dimensions and Weight |
Physical dimensions:
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: 900–1150 kg (1984–2535 lb) depending on configuration, turbocharger type, and aftertreatment hardware.
| Maintenance Data |
Oil and filter changes are typically recommended every 500 hours or manufacturer-specified mileage. Fuel filters should be replaced every 400–500 hours. Air filter replacement intervals vary from 200 to 400 hours depending on dust exposure. Coolant replacement typically occurs every two years or as coolant chemistry requires.
Valve lash should be checked on non-hydraulic variants. Aftertreatment systems require periodic regeneration, cleaning, and inspection depending on usage patterns. ECM logs assist predictive maintenance and troubleshooting.
| 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 ISX12 powers regional-haul tractors, vocational trucks, refuse trucks, cement mixers, fire trucks, transit buses, heavy agricultural machinery, wheel loaders, industrial cranes, large pumps, compressors, and certain generator platforms. Its strong torque curve, broad powerband, durability, and emissions capability make it suitable for global heavy-duty markets.
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