The Cummins Westport ISX12 G natural gas engine is a larger-displacement natural gas engine suitable for a variety of heavy-duty vehicles, including regional-haul truck/tractor, vocational, and refuse applications. With a displacement of 11.9 liters and up to 400 hp and 1450 lb-ft of torque, the ISX12 G is the natural choice when considering alternative fuel for demanding applications. The ISX12 G operates on 100% natural gas which can be carried on the vehicle in either compressed (CNG) or liquefied (LNG) form. The ISL G can also run on renewable natural gas (RNG).
Featuring the same proven Stoichiometric cooled Exhaust Gas Recirculation combustion technology, spark ignition and simple Three-Way Catalyst aftertreatment as the Cummins Westport ISL G engine, the ISX12 G delivers strong pulling power and heavy-duty durability and performance that customers can depend on.
For best reliability and durability, the recommended maximum GCVW for linehaul applications is 80,000 lb (36,287 kg). Recommended gearing to optimize fuel economy is 1400 to 1475 rpm at cruise speed for linehaul applications, and 1450 - 1600 rpm for vocational applications.
The ISX12 G meets current U.S. Environmental Protection Agency (EPA) and California Air Resource Board (ARB) emission standards and EPA greenhouse gas (GHG) and U.S. Department of Transportation fuel consumption regulations.
Note: The ISX12 G is no longer available. It has been replaced by the ISX12N—learn more here.
|Advertised Horsepower||400 hp||298 kW|
|Peak Torque||1450 lb-ft||1966 N•m|
|Governed Speed||2,100 rpm|
|Clutch Engagement Torque||700 lb-ft||949 N•m|
|Type||4-cycle, spark-ignited, inline 6-cylinder, turbocharged, CAC|
|Displacement||726.2 cu. in.||11.9 L|
|Bore and Stroke||5.11 in x 5.91 in||130 mm x 150 mm|
|Oil System Capacity||12 U.S. gal||45.4 L|
|Coolant Capacity||26.5 U.S. qts||25.1 L|
|Net Weight w/ Std. Accessories, Dry||2,650 lbs||1.202 kg|
|Fuel Types||CNG / LNG / RNG
Methane number 75 or greater
|Availability||Click here for OEM availability|
Cummins Westport engines can accept a wide range of natural gas fuel compositions.
Use our Fuel Performance Specification Calculator to ensure compatibility.
|Engine Model||Advertised Horsepower
lb-ft (N•m) @ rpm
|ISX12 G 400||400 (298)||1450 (1966) @ 1200||2100 rpm|
|ISX12 G 385||385 (287)||1350 (1830) @ 1200||2100 rpm|
|ISX12 G 350||350 (261)||1450 (1966) @ 1200||2100 rpm|
|ISX12 G 330||330 (246)||1250 (1695) @ 1200||2100 rpm|
|ISX12 G 320||320 (239)||1150 (1559) @ 1200||2100 rpm|
|ISX12 G 350R||350 (261)||1450 (1966) @ 1200||2100 rpm|
|ISX12 G 350R||350 (261)||1350 (1830) @1200||2100 rpm|
|ISX12 G 330R||330 (246)||1250 (1695) @ 1200||2100 rpm|
|ISX12 G 320R||320 (239)||1150 (1559) @ 1200||2100 rpm|
Overall, maintenance for the ISX12 G is similar to that of diesel engines, but there are a few key differences:
|Spin-on Fuel Filter||Daily Check|
|Oil And Filter*||500||25,000 mi (40,000 km)||6|
|Coolant Filter||1,500||75,000 mi (120,000 km)||12|
|Spin-on Fuel Filter||1,000||50,000 mi (80,000 km)||9|
|Spark Plugs||1,000||50,000 mi (80,000 km)||12|
|Overhead Set Adjustment**||3,000||150,000 mi (240,000 km)||24|
|Engine Brake Adjustment||6,000||300,000 mi (480,000 km)||24|
|Cooling System Flush||6,000||300,000 mi (480,000 km)||24|
|Ignition Coil Extension||10,000||500,000 mi (800,000 km)||5 yrs|
|Air cleaner / element||Follow vehicle manufacturers published recommendations|
|Oil and Filter*||500||7,500 mi (12,500 km)||6|
|Fuel Filter||1,000||15,000 mi (25,000 km)||9|
|Coolant Filter||1,500||22,500 mi (37,500 km)||12|
|Spark Plugs||1,000||15,000 mi (25,000 km)||12|
|Cooling System Flush||6,000||90,000 mi (150,000 km)||24|
|Overhead Set Adjustment**||3,000||45,000 mi (75,000 km)||24|
|Engine Brake Adjustment||6,000||90,000 mi (150,000 km)||24|
|Ignition Coil Extension||10,000||150,000 mi (240,000 km)||5 yrs|
|Air Cleaner / Element||Follow vehicle manufacturer's published recommendations|
^Based on normal duty cycle of 15 mph / 25 kph average speed. Distance intervals will increase or decrease based on average speed.
Refer to QuickServe Online or Owners Manual for complete details on maintenance intervals.
Watch a video overview of ISX12 G engine maintenance.