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Cummins/Onan G855 Engine

Name: Cummins/Onan G855 Engine
Brand: Cummins/Onan

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

1500 rpm

Rated speed

184 kW

Gross power

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Engine specifications

Rated speed	1500 rpm
Gross power	184 kW

Generator sets powered by this engine

Cummins/Onan G855 Series

How to read your Cummins/Onan engine serial & model number →

Common problems

Throttle plate is malfunctioning
Fix: Refer to a Cummins Authorized Repair Facility.
Engine-driven units are engaged
Fix: Disengage engine-driven units. Verify the correct starting procedure. Refer to Procedure 101-014 (Normal Starting Procedure) in Section 1.
Engine Will Not Reach Rated Speed (RPM)
Cause: Load is excessive for engine horsepower rating
Fix: Reduce the load on the engine.
Engine Will Not Crank or Cranks Slowly (Air Starter)
Cause: Starting procedure is not correct, Crankshaft rotation is impaired, Starting air pressure low, Starting circuit component is malfunctioning
Fix: Verify the correct starting procedure. Check the crankshaft for ease of rotation. Check that the air supply valve is open completely. Check the air compressor for proper operation. Check the starting circuit components.
Engine Vibration Excessive
Cause: Engine is misfiring, Fan is loose, damaged, or not balanced, Engine mounts are worn, damaged, or not correct
Fix: Check the fan. Check the engine mounts.
Engine Starts But Will Not Keep Running
Cause: Fuel valve closed (Manual), Load is excessive for engine horsepower rating, Air intake system restriction is above specification, Exhaust system resiriction is not within specification, Fuel supply pressure is below specification, Low or no fuel pressure at the mixer (secondary pressure)
Fix: Inspect the air intake system for restriction. Check the exhaust system for restrictions. Measure the fuel supply pressure.
Engine runs rough or misfires
Cause: Fuel leak
Engine runs rough at idle
Cause: STEP 1 Engine mounts are worn, damaged, or not correct STEP 2 Ignition system is malfunctioning or misfiring STEP 3 Intake air restricted STEP 4 Overhead adjustmenis are not correct
Engine power output low
Cause: STEP 1 Verify the complaint STEP 2 Load is excessive for engine horsepower rating STEP 3 Engine is misfiring STEP 4 Air intake or exhaust leaks STEP 5 Air intake system restriction is above specification STEP 6 Low or no fuel pressure at the fuel filter (primary pressure) STEP 7 Low or no fuel pressure at the fuel filter (secondary pressure)
Engine noise excessive
Cause: STEP 1 Lubricating oil pressure is below specification STEP 2 Coolant temperature is above specification STEP 3 Fan drive belt is loose, tight, or not in alignment STEP 4 Engine mounts are worn, damaged, or not correct STEP 5 Ignition system is malfunctioning or misfiring STEP 6 Overhead adjustments are not correct
Engine Difficult to Start or Will Not Start
Cause: STEP 1 Check the OEM fuel shutoff valves. Verify that the OEM manual fuel shutoff valve is closed fuel tanks are open.
Engine Decelerates Slowly
Cause: Compare the calibration in the electronic control system with the engine rating and the Control Parts Electronic control module system calibration is |............ List (CPL), Bulletin number 3379133 or 4021327. If not correct necessary, calibrate the system.
Fix: Refer to a Cummins Authorized Repair Facility.
Engine cranking speed is too slow
Fix: Inspect the air intake system for restriction. Replace the air filter. Refer to Procedure 010-059 (Air Cleaner Restriction) in Section 4 and Procedure 010-060 (Air Cleaner Element, Single Heavy Duty Dry Type) in Section 6.
Engine cranking speed is slower than 150 rpm
Fix: Refer to the Engine Will Not Crank or Cranks Slowly symptom tree.
Coolant Temperature Below Normal
Cause: Engine is operating at low ambient temperature
Fix: OK

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

Maintenance schedule

Item	Spec	Part #	Interval
Air filter	Clean and Inspect for Reuse, using solvent clean the air/mixer valve. Using compressed air to dry.	—	1500 hr
Fuel filter	Install a new filter element and replace the filter cover using a new o-ring seal.	—	1500 hr
Oil filter	7/16 capscrews, 3/8 capscrews	—	1500 hr
Battery	inductive charging and cranking system analyzer	—	1500 hr
Belt	Tighten the capscrews, Torque Value: 7/16 capscrews 27Nem [20 ft-lb], 3/8 capscrews 61Nem [45 ft-lb]	17900012	1500 hr	Amazon eBay
Coolant filter	Supplemental Coolant Additives (SCA) and Antifreeze? - Check	—	1500 hr
Oil	Lubricating Oil Level - Check	—	250 hr
Spark plug	Spark 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.

Service specifications

Type	Item	Value	Unit	Condition
Pressure	SAE J1349 test condition: barometric pressure	29.61	in. Hg	100 kPa; 300 ft (91 m) altitude
Pressure	SAE J1349 test condition: water pressure	0.30	in. Hg	1 kPa
Temperature	Rating note (1): water temperature to aftercooler, or use of air-to-air aftercooler with 100 F or lower air temperature to the radiator	32	C (90 F)	applies to 10.5:1 / 10:1 / 11:1 note-(1) ratings
Temperature	Rating note (2): water temperature to aftercooler, or use of air-to-air aftercooler with 130 F or lower air temperature to the radiator	54	C (130 F)	applies to 8.5:1 note-(2) ratings
Temperature	Rating note (3): water temperature to aftercooler, or use of air-to-air aftercooler with 110 F or lower air temperature to the radiator	32	C (90 F)	applies to 10.5:1 note-(3) ratings
Temperature	Rating note (4): water temperature to aftercooler, or use of air-to-air aftercooler with 130 F or lower air temperature to the radiator	54	C (130 F)	applies to 8.5:1 note-(4) ratings
Temperature	SAE J1349 test condition: inlet air temperature	77	F	25 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

Fluid	Grade	Standard	Ambient	Capacity	Notes
Fuel	dry processed natural gas				905 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.

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: Throttle plate is malfunctioning. Fix: Refer to a Cummins Authorized Repair Facility..