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Cummins/Onan NT855-G Engine

Name: Cummins/Onan NT855-G Engine
Brand: Cummins/Onan

The Cummins/Onan NT855-G is a 14 L 6-cylinder solenoid shift isochronous engine rated at 1800 rpm, producing up to 265 kW. It powers generator sets from Cummins/Onan, including the DFE 15R, DFE Series, DFP 17R and DFP 517. It holds 14 L (3.7 gal) of oil and 53 L (14.0 gal) of coolant.

Also known as: Cummins NT855-G

Part of the Cummins/Onan NT855 engine family — 6 variants share parts & fitment.

14.0 L

Displacement

Cylinders

1800 rpm

Rated speed

265 kW

Gross power

On this pageSpecs Generator sets Maintenance FAQ

Engine specifications

Oil capacity	14.0 L
Coolant capacity	53.0 L
Displacement	14.0 L
Cylinders	6
Aspiration	Solenoid Shift Isochronous
Rated speed	1800 rpm
Gross power	265 kW

Generator sets powered by this engine

Cummins/Onan DFE 15RCummins/Onan DFE SeriesCummins/Onan DFP 17R Cummins/Onan DFP 517

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

Common problems

Fault lamp lights, no fault exists.
Fix: To check a no-fault condition, disconnect leads from TB11 terminals 29, 30 and 31. If fault lamp lights with leads disconnected, replace engine monitor board. Reconnect leads.
Fault lamp lights immediately after engine starts.
Fix: Check for: Overspeed condition as engine starts.
Fault lamp lights and engine shuts down after running for a period.
Fix: Check the following: a. Oil level. Engine will shut down if sensor is closed. b. Check engine manual for troubleshooting oil system. c. High engine temperature. Check coolant level; check water flow (city water cooled systems); check radiator for free air flow, and fan belts for tightness. See engine manual for troubleshooting cooling system. d. Check for faulty oil pressure sensor or faulty high engine temperature sensor.
Engine stops cranking and fault lamp lights, after cranking approximately 75 seconds.
Fix: See engine service manual for troubleshooting fuel system. After correcting problem, reset engine monitor relay by placing Run-Stop/Reset-Remote switch to Stop/Reset position, then back to the required running position.
Overspeed shutdown.
Fix: Check governor and throttle linkages for freedom of movement. Check overspeed switch.
Overcrank fault lamp lights and engine stops cranking after approximately 75 seconds.
Fix: See engine service manual for troubleshooting fuel system. After correcting fault, reset engine monitor relay by placing Run-Stop/Reset-Remote switch to Stop/Reset position, depressing Reset button, then to the required running position.
Engine runs, shuts down, cranks for 75 seconds, cranking cycle stops, overcrank light ON.
Fix: Check fuel supply. a. Oil level. Replenish if necessary. b. Sensor. Faulty sensor will shut down engine. c. Refer to engine service manual for troubleshooting guide for oil system.
Overspeed shutdown
Fix: A. Check governor and throttle linkages for freedom of movement. b. Check overspeed switch.
Overspeed light on, no shutdown.
Fix: Disconnect wire at TB11-29. Light on after reset; replace engine monitor board.
Overspeed light on, no shutdown
Fix: Disconnect wire at TB11-29. Light on after reset; replace engine monitor board.
Overcrank fault lamp lights and engine stops cranking after approximately 75-seconds.
Fix: See engine service manual for troubleshooting fuel system. After correcting fault, reset engine monitor relay by placing Run-Stop/Reset-Remote switch to Stop/Reset position, depressing Reset button, then to the required running position.
Oil pressure shutdown
Fix: A. Check oil level; replenish if necessary. b. Check sensor; faulty sensor will shut down engine. c. Refer to engine service manual for troubleshooting guide for oil system.
Low oil pressure light ON, no shutdown
Fix: Disconnect wire at TB11-30. Light ON after relay reset. Replace engine monitor board.
High engine temperature shutdown
Fix: A. Check coolant level; replenish if necessary. b. For city water cooled sets, check water flow, valves, etc. c. Check sensor; check thermostat. d. Check radiator model, check fan belts, radiator for obstructions, etc.
High engine temperature light ON, no shutdown
Fix: Disconnect wire at TB11-31. Light ON after relay reset. Replace engine monitor board.

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan NT855-G.

Maintenance schedule

Item	Spec	Capacity	Part #	Interval
Air filter	Air Filter		—	500 hr
Fuel filter	Replace Fuel Filter		—	3000 hr
Oil filter	Replace Oil Filter Element		—	1000 hr
Battery	Battery		—	1000 hr
Belt	Belt		—	500 hr
Coolant	Coolant	53.0	—	1000 hr
Coolant filter	A shut off valve (see Figure 30) is installed in the inlet and outlet line to the coolant filter to be closed, for minimum coolant loss when the filter is removed. Refer to engine manufacturer's manual for coolant filter replacement information.		—
Oil	Engine Oil	40.0 gallons	—	500 hr
Spark plug	Spark Plug		—	500 hr

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

Parts cataloged across the Cummins/Onan NT855 family

133

Part #	Description	Category
140-2389	Cleaner, Air (Includes Element)	air_filter
140-2391	Element - Air Cleaner (Standard)	air_filter
CS-1382c	INLET AIR DAMPER	air_filter
ES-1214-2	FLOAT SWITCH	air_filter
191-1982	Pulley, Alternator	alternator
191-1983-02	Alternator, 24 Volt Spec B-O (Prestolite)	alternator
A956	2-12 VOLT BATTERIES	battery
2110153	Bell, End - Alt, to Exciter	bell
511-0092	Belt, Alternator	belt
805-35	Bolt, Place - Gen. Mtg. support to End Bell	bolt
1S0A713	Bracket, Overspeed Switch	bracket
2348115	Bracket, Mtg. - Volt. Cont. Reactor	bracket
234875	Bracket, Gate Reactor Mtg.	bracket
301A1914	Bracket, Panel Stop	bracket
319-2236	Bracket, Mounting	bracket
234070	Rig Assy., Brush- Incl. Brushes, & Contact Point Band, Gen. - Front Portion(Narrow)	brush
2I4AM	Brush	brush
505-0019	Bushing, Pipe - Reducer 1/2” to 3/8”, DFBF (1/2” to 3/8”) 505-0131 DFCB, DFCC, DFCE (3/4” to 3/8”)	bushing
518-0548-58	Clamp, Hose	clamp
2340116	Cover, Exciter	cover
0300-4623-08	DFBF (600V)	current_transformer
0300-4623-23	DFBF BR (0-480V)	current_transformer
FS1803s	FUEL FILTERS	fuel_filter
FP-KS12622A	NH/NT855 In-Frame Kit w/upper gasket set & oil pan gasket	gasket
FP-KS12622C	NH/NT855 In-Frame Kit w/upper gasket set & oil pan gasket	gasket
FP-KS12622C7	NH/NT855 In-Frame Kit w/upper gasket set & oil pan gasket	gasket
FP-KS12622D	NH/NT855 In-Frame Kit w/upper gasket set & oil pan gasket	gasket
M-4024945	Edge molded rubber head gaskets set	gasket
232A1817	Generator	generator
502-0827	Hose, Barb (1/2–14)	hose
503-0189	Clamp, Hose	hose
503-1634-01	Hose, Rubber (3/4” ID x 4”)	hose
302P465	RESISTOR-STABILIZING	meter
302P466	For 220/380-V, 3-Ph, 60-Cycle (Model H)	meter
302P468	For 120/208-V,120/240-V, & 347/600-V 3PH. 50 Cy!. (825-Ohm, 75-Watt)	meter
302P469	For 220/380-V, 3Ph. 50-Cycle	meter
302P470	For 277/480-V, 3-Ph, 50-Cyclo (5-P!)	meter
309-0641-03	Switch, Low Oil Pressure (S110)	oil_filter
102-1335	Plug, Oil Drain	other_service
102206606	Safety Messages	other_service
130-3588	Cap, Radiator	other_service
130-4355	Radiator (2 Row Core) DFBJ	other_service
130-4355-01	Radiator (3 Row Core) DFCF, DFCG	other_service
130-4369	Radiator DFCH	other_service
155-2409-01	Elbow, Exhaust (5" OD With Threads)	other_service
191-1981	Genset component (SJB series)	other_service
191-2121	Regulator, Voltage	other_service
232A1489	Generator support shim, 0.598 in gauge #6, 3x3	other_service
232A1490	Generator support shim, 0.359 in gauge #20, 3x3	other_service
301021151	Box Only, control	other_service
30118301	Bracket, Cont.Box Mtg. (Repl. 2-Piece Brkts)	other_service
301A2727	Handle , Control Box	other_service
302-213	60-Cycle	other_service
302-234	.Cycle	other_service
3028448	Plate, Mater Face	other_service
302P411	~~ Scale Reads 0-200 (1-Phase Use 2)	other_service
302P412	Scale Reads 0-250	other_service
302P414	Amm, Scale Reads 0-300 - Replaces 302-14.	other_service
302P415	Ammeter Scale Reads 0-500 - Replaces 302-371.	other_service
302P422	Scale Reads 0-600	other_service
302P423	Scale Reads 0-750 on side of Gen	other_service
302P467	For 277/480 Volt,3 Phase, 60 Cycle Plants.	other_service
303-111	Rheostat, Volt. Reg. - 175-Ohm, (Model H)	other_service
303-32	Knob, Rheos	other_service
3040305	45, 000-Ohm, 10-W - For 480-V , 3-Ph, 3-Wire & 277/480-V, 3+ Ph.	other_service
308-22	Switch, Volt. & Current Selector Ammeter	other_service
32082	3-Phase Models	other_service
320B18	Single Phase Models	other_service
333-0639-01	Heater, Coolant (4990 Watt)	other_service
333-0639-02	Heater, Coolant (6420 Watt)	other_service
337A44	Strap, Grd. - Unhoused Plants	other_service
402-78	Rubber, Mtg. - Cont. Box	other_service
503-1575	Clamp, V-Band	other_service
504-0011	Valve, Shutoff (1/2”)	other_service
505-0100	Nipple, Pipe - Close (1/2”)	other_service
526-0219	Washer, Flat (1/2)	other_service
800-0048	Screw, Cap - Hex Head (3/8-16 x 3/4”)	other_service
850-0050	Washer, Lock - Spring (3/8”)	other_service
870-0212	Nut, Locking (1/4-20)	other_service
960-0138		other_service
960-0606		other_service
EXS-1046s	CONDENSATION TRAP	other_service
FP-855PREM	NH/NT855 Premium Cylinder Kits	other_service
FP-855TT	NT855 Premium 3-Ring Cylinder Kits	other_service
FP-855TTDN	NT855 Premium 3-Ring Cylinder Kits Dual-NI Pistons	other_service
FP-855TTP	NT855 Premium Plus 3-Ring Cylinder Kits	other_service
FP-855TTPDN	NT855 Premium Plus 3-Ring Cylinder Kits Dual-NI Pistons	other_service
FP-IFK855NR	NT855 Cylinder Kits w/ no piston rings	other_service
FP-IFK855PREM	NH/NT855 Premium Cylinder Kits	other_service
FP-IFK855TT	NT855 Premium 3-Ring Cylinder Kits	other_service
FP-IFK855TTDN	NT855 Premium 3-Ring Cylinder Kits Dual-NI Pistons	other_service
FP-IFK855TTP	NT855 Premium Plus 3-Ring Cylinder Kits	other_service
FP-IFK855TTPDN	NT855 Premium Plus 3-Ring Cylinder Kits Dual-NI Pistons	other_service
FP-KS12621C	NH/NT855 Cylinder Kit Std Head Gask Grommets	other_service
FP-KS12621C7	NH/NT855 Cylinder Kit .010 Head Gask Grommets	other_service
FS1692s	FUEL SOLENOID VALVE LOCATION	other_service
M-1808	DC CONTROL WIRING	other_service
TB11-29	Engine Monitor Board	other_service
TB11-30	Engine Monitor Board	other_service
TB11-31	Engine Monitor Board	other_service
234C134	3-Phase	phase
234C137	3-Phase	phase
234C140	Single Phase	phase
234C141	Single Phase	phase
305P240	Rectifier, Volt. Cont.Reactor (Incl.in Rect. & Resistor A: 305P218)	reactor
305P233	Rectifier Assy., Power (Incl. two #305P234 wire & hardware)	rectifier
305P234	Rectifier Assy., Power (Field) (Incl. in Rect. #305P218)	rectifier
3ISA78	Rectifier, Voltage Control	rectifier
307-2621-02	Relay, Start Solenoid (K4)	relay
3044125	15,000-Ohm, 25-W - For 220/380-V, 3-Phase, 4-Wire	resistor
304PA76	Resistor, Volt. Cont.Reactor (Incl.in Rect.& Resistor A: 305P218)	resistor
3058227	Resistor Assy., Rect, & Incl. (Incl.in Rect. & Resistor A: 305P218)	resistor
204493	Ring, Collector	ring
800-0092	Screw, Cap - Hex Head (1/2-13 x 1.5)	screw
DM-3010461	Crankshaft Rear Seal - NT855, NTC855	seal
193-0432	Sender, Oil Temperature (S2 Engine Block, E4 Oil Pan)	sensor
193-0447-01	Sender, Water Temperature (E2)	sensor
193-0448	Sender, Oil Pressure	sensor
309-0269	Switch, Low Engine Temperature (S4)	sensor
309-0576	Switch, Thermostat - High Engine Coolant Temperature (S2)	sensor
309-0641-07	Switch, Oil Pressure (Closes at 20 lbs. Descending)	sensor
960-0504	PCC Control Service Manual	service_manual
960-0507	Detector Control Service Manual	service_manual
191-1858	Starter (24VDC)	starter
3320645	Strip, Marker - Volt. Con. Reactor (9305P218)	strip
5208190	Stud, Fixed Resistor Mtg.	stud
23201396	Support, Gen. Mtg.	support
1S0A717	Switch Assy., Overspeed	switch
B-342-3s	PRIMING TURBOCHARGER OIL SUPPLY INLET LINE. DISCONNECT AT THIS POINT TO PRIME	turbocharger
302P421	Scale Reads 0-300	voltmeter
304A15	S Washer, Fixed Resistor Cent. to Alternator End Bell	washer
508-0292	Washer, Sealing - Copper	washer
526-0029	*Washer, Flat (1/2")	washer

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

Common questions

What is the oil capacity of the Cummins/Onan NT855-G?

The Cummins/Onan NT855-G engine has an oil capacity of 14.0 liters.

What is the displacement of the Cummins/Onan NT855-G?

The Cummins/Onan NT855-G has a displacement of 14.0 liters with 6 cylinders.

Which generators use the Cummins/Onan NT855-G engine?

The Cummins/Onan NT855-G powers 4 generator set(s), including Cummins/Onan DFE 15R, Cummins/Onan DFE Series, Cummins/Onan DFP 17R, Cummins/Onan DFP 517.

How often should you change the oil in the Cummins/Onan NT855-G?

The Cummins/Onan NT855-G oil change interval is every 500 hours.

What is a common problem with the Cummins/Onan NT855-G engine?

A commonly reported issue on generators using the Cummins/Onan NT855-G is: Fault lamp lights, no fault exists.. Fix: To check a no-fault condition, disconnect leads from TB11 terminals 29, 30 and 31. If fault lamp lights with leads disconnected, replace engine monitor board. Reconnect leads..