ISL G Near Zero


ISL G Near Zero

The 2016 ISL G Near Zero (NZ) NOx natural gas engine is the first MidRange engine in North America to receive emission certifications from both the U.S. Environmental Protection Agency (EPA) and Air Resources Board (ARB) in California for meeting the 0.02 g/bhp-hr optional Near Zero NOx Emissions standards for medium-duty truck, urban bus, school bus, and refuse applications.

The game-changing Cummins Westport ISL G NZ exhaust emissions will be 90% lower than the current EPA NOx limit of 0.2 g/bhp-hr.  California ARB has defined this certified Near Zero emissions level of 0.02 g/bhp-hr NOx as equivalent to a 100% battery truck using electricity from a modern combined cycle natural gas power plant. The ISL G NZ will also meet the 2017 EPA greenhouse gas emission requirements with a 9% GHG reduction from the current ISL G.

Like the industry leading ISL G engine, the ISL G Near Zero will operate on 100% natural gas which can be carried on the vehicle in either compressed (CNG) or liquefied (LNG) form.  The ISL G Near Zero can also run on renewable natural gas (RNG). 

The ISL G NZ will be available as a first fit engine with truck, transit, school bus,  and refuse OEMs, as well as for engine replacement in  existing ISL G powered natural gas vehicles.

For additional information, visit

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Advertised Horsepower 320 hp 239 kW
Peak Torque 1,000 lb-ft 1,356 N•m
Governed Speed 2,200 rpm
Clutch Engagement Torque 550 lb-ft 746 N•m
Type 4-cycle, spark-ignited, inline 6-cylinder, turbocharged, CAC
Displacement 540 cu. in. 8.9 L
Bore and Stroke 4.49 in x 5.69 in 114 mm x 145 mm
Operating Cycles 4
Oil System Capacity 7.3 U.S. gal 27.6 L
Coolant Capacity 13.1 U.S. qts 12.4 L
System Voltage 12 V
Net Weight w/ Std. Accessories, Dry 1,625 lbs 737 kg
Aftertreatment Three-Way Catalyst (TWC)
Fuel Types CNG / LNG / Biomethane
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 Finder Specifications

Natural Gas
Certification Level EPA 2013
Power 250 - 320 hp / 186 - 239 kW
Torque 730 - 1000 lb-ft / 990 - 1356 N•m


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


Factory-Built, Dedicated Natural Gas Engine – Manufactured on the same assembly line as Cummins diesels, the ISL G Near Zero, like the ISL G, shares many components and parts with Cummins L Series diesels.

  • Electronic Control Module: Provides full monitoring and control of engine sensors, fuel system and ignition system, with full interface capability to Cummins INSITE and diagnostic service tools.
  • Three-Way Catalyst: Simple passive device, highly effective hydrocarbon, CO and NOx control with no maintenance costs. No Diesel Particulate Filter (DPF) or Selective Catalytic Reduction (SCR) systems are required.  The ISL G Near Zero catalyst includes a mid-catalyst temperature sensor connected to the ECM.
  • Closed Crankcase Ventilation (CCV):  The ISL G Near Zero features a chassis mounted CCV system that prevents crankcase emissions that are generated by the engine during normal operation from escaping into the atmosphere.  This reduces engine related Methane emissions by 70%,  by capturing crankcase emissions and redirecting them through the CCV filter where any oil is removed before sending crankcase gases back to the intake manifold to be reintroduced to the combustion chamber.
  • Low installed weight: Highest power:weight ratio in its class.
  • High-Energy Ignition System – Improved Ignition Control Module (ICM) provides better performance and improved spark plug and coil durability, plus self-diagnostics.
  • Fuel Capability - Natural gas can be stored on the vehicle in either compressed (CNG) or liquefied (LNG) form. The ISL G can also operate on renewable natural gas or biomethane that meets fuel-quality specifications.


Overall, maintenance for the ISL G Near Zero 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. For more information see the Product Information Bulletin available on

ISL G Near Zero Truck < 66,000 GVW

Maintenance Item Distance Hours Months
Check CAC cooler, piping, and air cleaner 7,500 mi (12,000 km) 250 3
Oil and Filter* 15,000 mi (24,000 km) 500 6
Fuel Filter 30,000 mi (48,000 km) 1,000 12
Coolant Filter 15,000 mi (24,000 km) 500 6
Crankcase Ventilation Filter change  --- 2,000 12
Spark Plugs 45,000 mi (72,000 km) 1,500 18
Coolant Change 60,000 mi (96,000 km) 2,000 24
Valve Adjustment** 60,000 mi (96,000 km) 2,000 24
Air Cleaner / Element Follow manufacturer's published recommendations
* Requires Natural Gas Engine Oil. 
**Initial valve adjustment at 1,000 hours.

ISL G Near Zero Urban Transit Bus and Refuse Truck

Maintenance Item^ Distance Hours Months
Oil and Filter* 7,500 mi (12,000 km) 500 6
Fuel Filter 15,000 mi (24,000 km) 1,000 12
Coolant Filter 7,500 mi (12,000 km) 500 6
Crankcase Ventilation Filter Change     -- 2,000 12
Spark Plugs 22,500 mi (36,000 km) 1,500 18
Coolant Change 30,000 mi (48,000 km) 2,000 24
Valve Adjustment** 30,000 mi (48,000 km) 2,000 24
Air Cleaner / Element Follow manufacturer's published recommendations

* Requires Natural Gas Engine Oil 
**Initial valve adjustment at 1,000 hours.
^Based on normal duty cycle of 15 mph average speed.  Distance intervals will increase or decrease based on average speed.  

  • Default interval is the hours stated. Interval is whichever comes first – hours, miles or time.
  • Refer to QuickServe® Online or Owners Manual for complete details on maintenance intervals.

Brochures Available

Title Bulletin Number Request View  
2017 School Bus Market Brochure 5410584 Request View  Download
Cummins Westport ISL G Near Zero Fact Sheet View  Download