ISL G for Medium-Duty Truck (2013)


ISL G for Medium-Duty Truck (2013)

The ISL G is the newest evolution of alternative fuel engine technology, combining all the advantages of clean-burning, natural gas engines with "no compromise" performance for medium duty truck, refuse truck, shuttle bus, urban transit, school bus, vocational and urban truck/tractor pick up-and-delivery applications. The ISL 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 (DOT) fuel consumption regulations.

Ratings range from 250-320 horsepower (186-239 kw). Standard features include proven wastegate turbo technology for impressive low-end torque and transient response, with an increase in fuel efficiency. These features give the ISL G outstanding reliability and durability.

Plus, the ISL G sets a new benchmark for lower alternative fuel vehicle life cycle costs. In high fuel use applications, the combination of lower alternative fuel costs, improved fuel economy and lower incremental maintenance costs make it possible to save valuable dollars with a natural gas powered fleet. The ISL G can also operate on biomethane -- renewable natural gas made from biogas or landfill gas that has been upgraded to pipeline and vehicle fuel quality.  Biomethane fuel is carbon dioxide (CO2) neutral.

As with all our alternative fuel engines, the ISL G comes with one of the best base warranties in the industry.  All backed by the largest customer support network in the industry. For additional information, visit

Considering a Cummins engine purchase? For more information including pricing and additional technical information, please contact your Cummins representative. If you need help finding a representative, the Cummins Sales and Service Locator tool can help.


Cummins PowerSpec is an electronic tool that makes it possible to tailor the operation of Cummins engines in every on-highway application.

Available for: On-Highway, Medium-Duty Truck, Natural Gas

See ISL PowerSpec Engine Features


The ISL G engine is an excellent choice for 32,000-66,000 (14,515-29,937 kg) lb GCW/GVW short-haul applications and regional haul trucks, shuttle and school buses, urban transit buses, articulated buses, and on-/off-highway applications such as larger refuse and dump trucks. The high torque and broad power band of the ISL G provides excellent performance when matched to various manual and automatic transmissions.

Enhanced electronics provide the ability to compensate for variations in fuel quality and operating conditions, providing every alternative in fuel choices. The ISL G is capable of operating on compressed or liquefied natural gas (CNG, LNG) or biomethane that meets Cummins minimum fuel quality specifications.

Maximum Horsepower 250-320 hp 186-239 kW
Peak Torque 660-1000 lb-ft 895-1356 N•m
Governed Speed 2100-2200 rpm
Clutch Engagement Torque 550 lb-ft 746 N.m
Type 4 cycle, spark-ignited inline 6-cylinder, turbocharged, CAC
Engine Displacement 540 cu in 8.9 Liters
Bore and Stroke 4.49 x 5.69 in 114 x 144.5 mm
Operating Cycles 4
Oil System Capacity 7.3 U.S. gal 27.6 Liters
Coolant Capacity 13.1 U.S. qt 12.4 Liters
System Voltage 12 V
Net Weight w/std Accessories, Dry 1,500 lb 680 kg

Product Finder Specifications

Natural Gas
Certification Level EPA 2013
EPA 2010
Power 250 - 320 hp / 186 - 239 kW
Torque 660 - 1100 lb-ft / 895 - 1491 N•m


Engine Model Advertised hp (kW) @ rpm Peak Torque lb-ft (N•m) @ rpm Governed Speed @ rpm
ISL G 320 320 (239) @ 2000 1000 (1356) @ 1300 2200
ISL G 300 300 (224) @ 2100 860 (1166) @ 1300 2200
ISL G 280 280 (209) @ 2000 900 (1220) @ 1300 2200
ISL G 260 260 (194) @ 2200 660 (895) @ 1300 2200
ISL G 250 250 (186) @ 2200 730 (990) @ 1300 2200

For more information, call your local Cummins distributor or Cummins Westport representative, or visit


  • Air Intake System: Charge air cooling reduces emissions by lowering intake manifold air temperatures.

  • Accessory Belt Drive System: Self-tensioning serpentine polyvee belt accessory drive system for water pump, engine-mounted fan hub and most alternators.

  • Three-Way Catalyst: Required for all models. Certified to US EPA 2010 standard and California Air Resources Board standards. Meets EPA useful life requirement of up to 290,000 miles (464,000 km) in transit applications with no scheduled maintenance.

  • High Energy Ignition System: Provides better performance and longer service intervals, improved spark plug and coil durability, plus self-diagnostics.

  • High Efficiency Lube Cooler: Lowers oil temperatures for longer engine life.

  • Control System: Full drive-by-wire. Electronic Control Module (ECM) provides full monitoring and control of engine sensors, fuel system and ignition system. Full interface capability to Cummins INSITE™ and QuickCheck diagnostic service tools. Control Module provides OEMs and end users with the ability to tailor performance of the engine to fit the vehicle mission.

  • Crankshaft: Eight counterweight, fully balanced, high-tensile-strength steel forging with induction-hardened fillets and journals for outstanding durability.

  • Oil Filter: The combination full-flow and bypass oil filter improves filtration while minimizing oil filter replacement and disposal costs.

  • Wastegated Turbocharger: With electronic control for precise air handling. Water-cooled bearing housing for durability.

  • The 8.9 liter ISL G uses stoichiometric cooled Exhaust Gas Recirculation combustion (EGR) leveraging Cummins proven EGR technology to create a high-performance natural gas engine.

    The cooled EGR system takes a measured quantity of exhaust gas, passes it through a cooler to reduce temperatures before mixing it with the incoming air charge to the cylinder. The use of cooled EGR (in place of large amounts of excess air) not only lowers combustion temperatures like our current Lean Burn technology, it also allows the creation of oxygen-free exhaust, which in turn allows for the use of a Three Way Catalyst (TWC). TWCs are simple passive devices that are maintenance free and have been commonly used in passenger cars since the 1970's.

    Stoichiometric cooled EGR combustion improves power density as well as fuel economy - important benefits that fleets will enjoy every day. In fact, low speed torque is improved by over 30% compared to previous engines.


Overall, maintenance for the ISL G is similar to that of diesel engines, but there are a few key differences: 

Motor oil specifically formulated for natural gas engines is required.  Do not use diesel engine oil in a natural gas engine. If diesel engine oil is used, valve torching, piston scuffing and reduction in spark-plug life will occur.

ISL G Truck < 66,000 lbs (29,937 kg) GCVW

 Maintenance Item^ Miles (Kilometers) Hours Months
Check CAC cooler, piping and Air cleaner 7,500 mi (12,000 km) 250 3
Oil and Filter* 15,000 (24,000) 500 6
Fuel Filter 30,000 (48,000) 1,000 12
Coolant Filter 15,000 (24,000) 500 6
Spark Plugs 45,000 (72,000) 1,500 18
Cooling System Flush 60,000 (96,000) 2,000 24
Overhead Set Adjustment** 60,000 (96,000) 2,000 24
Ignition Coil Adjustment 300,000 (480,000 km) 10,000 5 yrs
Air Cleaner / Element Follow Manufacturer's published recommendations

^Based on a duty cycle of 30 mph / 48 kph average speed.  Distance intervals will increase or decrease based on average speed.
*Requires Natural Gas Engine Oil.  For customers using CES 20092 natural gas enines oils only, the recommended interval is 1,000 hrs
**Initial overhead set adjustment at 1,000 hours

ISL G Urban Transit Bus & Refuse Truck

 Maintenance Item^ Miles (Kilometers) Hours Months
Oil and Filter* 7,500 (12,000) 500 6
Fuel Filter 15,000 (24,000) 1,000 12
Coolant Filter 7,500 (12,000) 500 6
Spark Plugs^ 22,500 (36,000) 1,500 18
Coolant System Flush 30,000 (48,000) 2,000 24
Overhead Set Adjustment** 30,000 (48,000) 2,000 24
Ignition Coil Extension 150,000 (240,000) 10,000 5 yrs
Air Cleaner / Element Follow manufacturer's published recommendations

^Based on a duty cycle of 15 mph / 48 kph average speed.  Distance intervals will increase or decrease based on average speed.
*Requires Natural Gas Engine Oil.  For customers using CES 20092 natural gas enines oils only, the recommended interval is 1,000 hrs
**Initial overhead set adjustment at 1,000 hours

Default interval is the hours stated. Interval is whichever comes first - hours, miles or time.

For complete maintenance information, please consult your Owner's Manual or Operations and Maintenance Manual, available on QuickServe Online.

Brochures Available

Title Bulletin Number Request View  
Cummins Natural Gas Parts Brochure 2878880 View  Download
Cummins Westport ISL G Brochure 4971499 Request View  Download
Cummins Westport ISL G Brochure – French 4971503 Request View  Download
Driver Tips Card For Natural Gas Engines 4971392 Request View  Download
Driver Tips Card For Natural Gas Engines - French 4971422 Request View  Download
Encore Xtra Extended Coverage Folder 5410594 View  Download
Encore Xtra Extended Coverage For North American Dealers Brochure 5410591 Request View  Download
Encore Xtra Extended Coverage For North American Dealers Brochure - French 5410622 Request View  Download
Encore Xtra Trifold Brochure 2878926 Request View  Download
Encore Xtra Trifold Brochure - French 5410602 Request View  Download
School Bus Engines Brochure (2013) 4971393 Request View  Download
Urban Transit Brochure (2013) 4971427 Request View  Download