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Home›Engines›Cummins/Onan G855

Cummins/Onan G855 Engine

The Cummins/Onan G855 is an engine rated at 1500 rpm, producing up to 184 kW. It powers generator sets from Cummins/Onan, including the G855 Series.

Also known as: Cummins G855

Part of the Cummins/Onan G855 engine family — 2 variants share parts & fitment.

1500 rpm
Rated speed
184 kW
Gross power
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Engine specifications

Rated speed1500 rpm
Gross power184 kW

Common problems

15
  • Engine Will Not Reach Rated Speed (RPM)
    Cause: Load is excessive for engine horsepower rating
    Fix: Reduce the load on the engine. Refer to OEM specifications.
  • Engine Transient Response Poor
    Cause: Load is excessive for engine horsepower rating
    Fix: Reduce the load on the engine. Refer to OEM specifications.
  • Engine Power Output Low
    Cause: Verify the complaint
    Fix: Test the engine operation while under load. Perform an engine acceleration test. Perform an engine load/install test. Refer to the OEM installation instructions.
  • Coolant Temperature Above Normal - Gradual Overheat
    Cause: Coolant level is below specification
    Fix: Inspect the engine and cooling system for external coolant leaks. Repair if necessary. Add coolant. Refer to Procedure 018-018 (Cooling System) in Section V.
  • Fuel Consumption Excessive
    Cause: Verify the complaint
    Fix: Refer to the engine datasheet. Compare the fuel usage records with the engine datasheet.
  • Engine Starts But Will Not Keep Running
    Cause: Manual fuel valve closed
    Fix: Open manual fuel valve.
  • Engine Noise Excessive
    Cause: Lubricating oil pressure is below specification
    Fix: Check the oil pressure. If the pressure is low, refer to the Lubricating Oil Pressure Low symptom tree.
  • Engine Acceleration or Response Poor
    Cause: Verify the complaint
    Fix: Refer to the Human Machine Interface, if available or an electronic service tool to verify system faults and system status. Contact a Cummins Authorized Repair Facility if an electronic service tool is required.
  • Coolant Loss - External
    Cause: Coolant level is above specification
    Fix: Check the coolant level. Refer to Procedure 008-066 (Coolant Level) in Section 3.
  • Engine Difficult to Start or Will Not Start
    Cause: OEM manual fuel shutoff valve is closed
    Fix: Check the OEM fuel shutoff valves. Verify that the fuel tanks are open.
  • Lubricating Oil Sludge in the Crankcase Excessive
    Cause: Lubricating oil drain interval is excessive
    Fix: Verify the correct lubricating oil drain interval. Refer to Procedure 102-002 (Maintenance Schedule) in Section 2.
  • Lubricating Oil Pressure Low
    Cause: Lubricating oil level is above or below specification
    Fix: Check the oil level. Add or drain oil if necessary. Refer to Procedure 007-043 (Lubricating Oil Level) in Section 3 and Procedure 007-002 (Lubricating Oil and Filters) in Section 4. Check the dipstick calibration.
  • Lubricating Oil Consumption Excessive
    Cause: Lubricating oil leak (external)
    Fix: Inspect the engine for external oil leaks. Tighten the capscrews, pipe plugs, and fittings. Replace gaskets, if necessary. Refer to Procedure 018-009 (Capscrew Markings and Torque Values) in Section V torque for specifications.
  • Engine Will Not Crank or Cranks Slowly (Air Starter)
    Cause: Starting procedure is not correct
    Fix: Verify the correct starting procedure. Refer to Procedure 101-014 (Cold Weather Starting) in Section 1.
  • Engine Runs Rough at Idle
    Cause: Engine mounts are worn, damaged, or not correct
    Fix: Inspect the engine mounts. Replace as needed. Refer to a Cummins Authorized Repair Facility.

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan G855.

Maintenance schedule

ItemSpecCapacityPart #Interval
Air filterClean and Inspect for Reuse, using solvent clean the air/mixer valve. Using compressed air to dry.—1500 hr
Fuel filterInstall a new filter element and replace the filter cover using a new o-ring seal.—1500 hr
Oil filter7/16 capscrews, 3/8 capscrews—1500 hr
Batteryinductive charging and cranking system analyzer—1500 hr
BeltTighten the capscrews, Torque Value: 7/16 capscrews 27Nem [20 ft-lb], 3/8 capscrews 61Nem [45 ft-lb]179000121500 hr Amazon eBay
Coolant filterSupplemental Coolant Additives (SCA) and Antifreeze? - Check—1500 hr
OilLubricating Oil Level - Check—250 hr
Spark plugSpark Plugs- Check—1500 hr

Pooled from every document that names this exact engine — confirm the interval and part number against your unit's serial number.

Repair guides

6

Step-by-step procedures compiled from the Cummins/Onan service manual for this engine.

Service specifications

7
TypeItemValueUnitCondition
PressureSAE J1349 test condition: barometric pressure29.61in. Hg100 kPa; 300 ft (91 m) altitude
PressureSAE J1349 test condition: water pressure0.30in. Hg1 kPa
TemperatureRating note (1): water temperature to aftercooler, or use of air-to-air aftercooler with 100 F or lower air temperature to the radiator32C (90 F)applies to 10.5:1 / 10:1 / 11:1 note-(1) ratings
TemperatureRating note (2): water temperature to aftercooler, or use of air-to-air aftercooler with 130 F or lower air temperature to the radiator54C (130 F)applies to 8.5:1 note-(2) ratings
TemperatureRating note (3): water temperature to aftercooler, or use of air-to-air aftercooler with 110 F or lower air temperature to the radiator32C (90 F)applies to 10.5:1 note-(3) ratings
TemperatureRating note (4): water temperature to aftercooler, or use of air-to-air aftercooler with 130 F or lower air temperature to the radiator54C (130 F)applies to 8.5:1 note-(4) ratings
TemperatureSAE J1349 test condition: inlet air temperature77F25 C

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Recommended fluids

FluidGradeStandardAmbientCapacityNotes
Fueldry processed natural gas905 BTU per standard cubic foot (33.72 kJ/l) lower heating value, used for the tabulated ratings; deration may be required due to altitude, temperature, type of fuel or use of a catalytic converter

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Parts cataloged across the Cummins/Onan G855 family

34
Part #DescriptionCategory
06600154Air cleaner tubeAir cleaner
05e00009filter element, NGAir filter
17900012Drive Belt, Cooling FanBelt
10200031Fan, CoolingFan
03900242Coolant FilterFilter
03900243Coolant FilterFilter
03900244Coolant FilterFilter
03900245Coolant FilterFilter
081000714RESTORE™ CC2610 1 - GallonFluid
03100050Overhead SetGasket
03100052Crosshead Adjusting Screw Lock NutGasket
03100066Rocker Lever CoverGasket
03100067Rocker Lever CoverService part / kit
03100069Rocker Lever CoverService part / kit
0500007filter coverService part / kit
06400190Air/fuel mixer power valveService part / kit
08100072BeltsService part / kit
08100073Catalytic ConvertersService part / kit
08100074ClutchesService part / kit
08400190capscrew, 7/16Service part / kit
08600155capscrew, 3/8Service part / kit
08600156capscrew, 7/16Service part / kit
3376592Inch Pound Torque WrenchService part / kit
3822735Plastic bead blasting mediaService part / kit
03100058Overhead SetOverhead set
08900235Low-Temperature Aftercooler (LTA) Water PumpPump
08900236Low-Temperature Aftercooler (LTA) Water PumpPump
089002397Low-Temperature Aftercooler (LTA) Water PumpPump
08900246Low-Temperature Aftercooler (LTA) Water PumpPump
08900247Low-Temperature Aftercooler (LTA) Water PumpPump
09900238Low-Temperature Aftercooler (LTA) Water PumpPump
03100063Rocker Lever CoverRocker lever cover
03100064Rocker Lever CoverRocker lever cover
08400269Spark Plug WireSpark plug

Parts cataloged across all variants of this engine family — verify the exact part fits your specific variant and serial number before ordering.

Common questions

Which generators use the Cummins/Onan G855 engine?

The Cummins/Onan G855 powers 1 generator set(s), including Cummins/Onan G855 Series.

How often should you change the oil in the Cummins/Onan G855?

The Cummins/Onan G855 oil change interval is every 250 hours.

What is a common problem with the Cummins/Onan G855 engine?

A commonly reported issue on generators using the Cummins/Onan G855 is: Engine Will Not Reach Rated Speed (RPM). Cause: Load is excessive for engine horsepower rating. Fix: Reduce the load on the engine. Refer to OEM specifications..