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Cummins/Onan RDJF Engine

The Cummins/Onan RDJF is a 2.3 L 4-cylinder naturally aspirated engine rated at 1800 rpm. It powers generator sets from Cummins/Onan, including the 17.5RDJF-3CR and 20W-20. It holds 6.15 L (1.6 gal) of oil and 11.36 L (3.0 gal) of coolant.

Also known as: Onan RDJF

2.3 L

Displacement

Cylinders

1800 rpm

Rated speed

6.15 L

Oil capacity

On this pageSpecs Generator sets Maintenance FAQ Service intervals Torque & specs Fluids Procedures

Engine specifications

Oil capacity	6.15 L
Coolant capacity	11.36 L
Displacement	2.3 L
Cylinders	4
Aspiration	Naturally Aspirated
Rated speed	1800 rpm

Generator sets powered by this engine

Cummins/Onan 17.5RDJF-3CR Cummins/Onan 20W-20

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

Troubleshooting

Symptoms & remedies

Symptom	Cause	Remedy
No build up of AC output voltage — Is Field Breaker CB21 on control panel ON?		Proceed to step 2 if YES; proceed to step 3 if NO
No build up of AC output voltage — Connect jumper wire across terminals of Field Breaker, CB21. Does AC output voltage build up?	Field breaker defective	If voltage builds up REPLACE FIELD BREAKER; if not, proceed to step 4
No build up of AC output voltage — Push to reset Field Breaker. Does AC output voltage build up?		If voltage builds up but is high, low, unstable, or causes tripping of Field Breaker, refer to Tables B, C, or D
No build up of AC output voltage — Disconnect alternator stator leads 1 & 2 from TB21-1 and TB21-2 on VR22. Is reference voltage across 1 & 2 20 VAC or more?		Proceed to step 14 if YES; proceed to step 13 if NO
No build up of AC output voltage — Is exciter field voltage across F1+ and F2- on endbell terminal block 7.0 VDC or more?	Wiring harness W9 from end bell to VR22 terminals 3 and 4 may be faulty	If not, check wiring harness W9 from end bell to VR22 terminals 3 and 4
No build up of AC output voltage — Are diodes CR1, CR2, CR3, CR4, CR5, CR6 in rotating rectifier assemblies OK?	Defective diode(s) — check all diodes, more than one may be defective
No build up of AC output voltage — Flash exciter field. Is reference voltage across 1 and 2 now 20 VAC or more?		Proceed to step 14 if YES; proceed to step 13 if NO
No build up of AC output voltage — Reconnect generator leads 1 & 2 to TB21-1 and TB21-2 on VR22. Does reference voltage build up?		Proceed to step 15 if YES; proceed to step 13 if NO
No build up of AC output voltage — Is regulator DC output voltage across VR21-7 and VR21-8 7 VDC or more?		Proceed to step 16 if YES; proceed to step 18 if NO
No build up of AC output voltage — Are SCR's CR13 and CR16 OK?		Proceed to step 17 if YES; proceed to step 18 if NO
No build up of AC output voltage — Are diodes CR12, CR14, and CR15 OK?		Proceed to step 18 if YES; proceed to step 18 if NO
No build up of AC output voltage — Replace voltage regulator PC board (VR21)		Replace voltage regulator PC board (VR21)
AC output voltage builds up, but is unstable — Are there any loose or broken wires or connections on voltage regulator assembly VR22?	Loose or broken wires or connections on voltage regulator assembly VR22	Proceed to step 2 if YES; proceed to step 2 if NO
AC output voltage builds up, but is unstable — Is W9 (exciter field) wiring harness from VR22 to End bell OK?		Proceed to step 3 if YES; proceed to step 4 if NO
AC output voltage builds up, but is unstable — Does adjustment of Damping Control R27 potentiometer on VR21 result in stable voltage?		Proceed to step 4 if YES; proceed to Test Procedure A if NO
AC output voltage builds up, but is unstable — Replace		Replace
Engine does not crank — Check 12 VDC to ground at battery BT1 and at starter motor B1. Check B+ present at TB11, K11, K13, S1, and M11.		Proceed to step 2 if YES; proceed to Test Procedure A, G if NO
Engine does not crank — Is battery dead? Check if centrifugal switch S1 is open to ground. If S1 remains closed when set is shutdown, R11 and K14 will discharge through S1 to ground. Remove switch cover and check operation manually.	Centrifugal switch S1 remains closed when set is shutdown, causing R11 and K14 to discharge through S1 to ground	Remove switch cover and check operation manually
Engine does not crank — Replace S1. Replace or charge battery.		Replace S1; Replace or charge battery
Engine does not crank — Jumper battery cable connection to ground at starter. Does engine crank?		Proceed to step 6 if YES; proceed to step 7 if NO
Engine does not crank — Check starter motor. Repair or replace.	Starter motor faulty	Repair or replace
Engine does not crank — With S11 at START, is at least 7 volts present between terminal S on K11 and ground. Does K11 energize?		Proceed to step 8 if YES; proceed to step 10 if NO
Engine does not crank — Does manual operation of K11 crank engine?		Proceed to step 9 if YES; proceed to step 10 if NO
Engine does not crank — Jumper K11 from B+ to S terminal. Does engine crank?		Proceed to step 10 if YES; proceed to step 11 if NO
Engine does not crank — Start relay K11 is defective; replace.	Start relay K11 defective	Replace
Engine does not crank — With S11 at START, jumper K11 contacts to starter solenoid. Does engine crank?		Proceed to step 11A if YES; proceed to step 12 if NO
Engine does not crank — Replace K11.		Replace K11
Engine does not crank — With S11 at START, jumper normally closed contacts of K12. Does engine crank and start?		Proceed to step 13 if YES; proceed to step 10 if NO
Engine does not crank — Replace K12.		Replace K12
Engine cranks but does not start — Is 12 VDC present between start terminal on S11 and ground (TB11-1) with S11 at START?		Proceed to step 2 if YES; proceed to Test Procedure G if NO
Engine cranks but does not start — Is 12 VDC present between M11-B+ and ground TB11-1 with S11 at START? Check Wire W3 & W8.		Proceed to step 3 if YES; proceed to step 4 if NO
Engine cranks but does not start — Replace faulty switch S11.	Faulty switch S11	Replace faulty switch S11
Engine cranks but does not start — Does engine operate on gasoline? Is fuel primer solenoid K3 energized when S11 is at START?		Proceed to step 6 if YES; proceed to step 9 if NO
Engine cranks but does not start — Remove fuel solenoid from fuel line and press S11. Does fuel pulsate from line?		Proceed to step 9 if YES; proceed to step 12 if NO
Engine cranks but does not start — Check lead from TB12-4 to fuel pump; check fuel pump and replace if necessary.	Faulty fuel pump or lead from TB12-4 to fuel pump	Check lead from TB12-4 to fuel pump; check fuel pump and replace if necessary
Engine cranks but does not start — Check engine oil level. If okay, remove LOP switch S4 lead at TB12-4. Does engine crank and run when S11 is pressed?		Proceed to step 11 if YES; proceed to step 13 if NO
Engine cranks but does not start — Is lead 6 from TB12-6 to LOP switch S4 grounded?		Proceed to step 12 if YES; proceed to Test Procedure G if NO
Engine cranks but does not start — Repair or replace lead 6 to S4.	Lead 6 to S4 faulty	Repair or replace lead 6 to S4
Engine cranks but does not start — If necessary, replace LOP switch S4.		If necessary, replace LOP switch S4

Fault codes and symptom→remedy steps extracted from this engine’s service/owner documentation; verify against the official manual before servicing.

Common problems

Engine fails to start — little or no fuel flow from return line
Cause: Fuel supply system problem
Fix: Check fuel supply system: fuel tank empty?; shutoff valves closed?; fuel lines kinked?; loose connections?; clogged fuel filters?
Engine fails to start — fuel flows steadily from return line
Cause: Preheat system problem
Fix: Observe air heater thru air inlet; engage preheat; if heater element does not glow red within 30 seconds, check air heater and glow plug wiring: connections tight?; free from corrosion?
Stop circuit fails (set does not stop)
Fix: Close fuel valve
Engine still does not start
Fix: Contact authorized Onan service representative
Engine fires but does not start
Fix: Repeat starting procedures, including preheat; limit cranking to 15 to 20 seconds to conserve battery; if engine still does not start, see "If Engine Fails to Start" information
Engine fails to start — little or no exhaust smoke (engine is not getting fuel)
Cause: Engine is not getting fuel
Fix: Prime fuel system; observe fuel flow from return line

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

Maintenance schedule

Item	Spec	Capacity	Part #
Air filter	Dry		—
Fuel filter			—
Oil filter	Full Flow Type		—
Battery			—
Belt			—
Coolant			—
Oil	Type: Light	11.36 quarts	—
Spark plug			—

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

Service intervals

Item	Action	Hours	Notes
Engine	Inspect	8 hr
Exhaust system	Inspect	8 hr
Fuel supply	Check	8 hr	See Note 1
Oil level	Check	8 hr
Air cleaner	Check	50 hr	More often in dusty conditions
Crankcase oil	Change	100 hr	First service — After first 50 hours of operation; drain while engine is still hot
Cylinder head bolts	Check	50 hr	First service — Retighten after first 50 hours on an overhauled engine
Valve clearance	Adjust	50 hr	First service — After first 2 to 50 hours of operation
Fuel condensation traps in lines and filters	Drain	100 hr
Governor linkage	Clean	100 hr
Battery	Check	200 hr
Oil filter	Replace	200 hr
Breather standpipes	Clean	500 hr
Start-disconnect circuit	Check	500 hr
Valve clearances	Check	500 hr
Primary fuel filter	Change	600 hr
Nozzle spray pattern	Test	2000 hr	Trained diesel injection personnel only (Note 2)
Rocker box oil line and orifices	Clean	2000 hr
Valves	Other	2000 hr	Grind valves (if required)
Secondary fuel filter	Change	3000 hr
Engine	Other	5000 hr	General overhaul (if required)

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

Service specifications

Type	Item	Value	Unit	Condition
Clearance	Camshaft bearing clearance (original)	.0015-.0030	inch
Clearance	Camshaft bearing clearance (replacement)	.0012-.0037	inch
Clearance	Camshaft end play	0.007-0.039	inch	room temperature 70 F
Clearance	Connecting rod bearing clearance (original)	.001-.0033	inch
Clearance	Connecting rod bushing clearance	.0002-.0007	inch
Clearance	Connecting rod end play	.002-.016	inch
Clearance	Crankshaft end play	0.010-0.015	inch
Clearance	Cylinder bore honed diameter	3.4995-3.5005	inch
Clearance	Exhaust valve guide clearance	.0030-.0050	inch
Clearance	Main bearing journal diameter	2.2427-2.2435	inch
Clearance	Piston clearance in cylinder	0.0055-0.0075	inch	90 deg to pin, below oil ring
Gap	Oil pump gear lash	0.005	inch
Gap	Piston ring gap	0.010-0.020	inch
Gap	Starter armature end play	.005-.030	inch
Gap	Starter pinion clearance to pinion stop	.070-.120	inch	Solenoid plunger bottomed
Gap	Valve head to cylinder head face clearance	0.030	inch	minimum
Gap	Valve seat width	.047-.062	inch	45 degree seat angle
Pressure	Cylinder compression	350-400	psi	cranking at about 300 rpm
Pressure	Delivery valve line pressure	300 to 600	psi	engine running
Pressure	Exhaust back pressure limit	27	inches of water	rated load
Pressure	Fuel pump vacuum	15 to 18	inches	sea level
Pressure	Fuel transfer pump pressure	12-14	psi	at 1800 rpm
Pressure	Injection nozzle adjusted opening pressure	1750	psi
Pressure	Injection nozzle opening pressure	1900 to 1950	psi
Pressure	Minimum oil pressure at governed speed	20	psi	inspect oil system if below
Pressure	Normal oil pressure	25	psi	engine at operating temperature (or higher)
Pressure	Oil bypass valve opening pressure	25	psi
Resistance	Battery specific gravity	1.290 to 1.225		75 percent charged
Speed	Governor maximum governed speed	2400	rpm
Speed	Start-disconnect switch disengage speed	900	rpm	about
Temperature	Cylinder head oven temperature for valve seat installation	325	deg C	about 1/2 hour
Temperature	Ring gear installation oven temperature	380-400	deg F	30 to 40 minutes
Temperature	Thermostat opening temperature	150 +/- 2	deg F
Temperature	Timing gear heating temperature	350	deg F	electric burner or oven
Torque	Center main bolt (4 cylinder)	97-102	ft-lb
Torque	Connecting rod bolt	27-29	ft-lb
Torque	Cylinder head bolt	44-46	ft-lb
Torque	Cylinder head bolt (first step)	25-30	ft-lb
Torque	Delivery valve cap nut	55-60	ft-lb
Torque	Delivery valve holder	75-80	ft-lb	Maximum
Torque	Exhaust manifold nuts	13-15	ft-lb	Tighten evenly
Torque	Flywheel mounting screw	65-70	ft-lb
Torque	Fuel pump mounting screws	15-20	ft-lb
Torque	Gear case cover	18-20	ft-lb
Torque	Gear cover mounting screws	15-20	ft-lb
Torque	Glow plug	10-15	ft-lb
Torque	Injection nozzle mounting screws	20-21	ft-lb
Torque	Injection pump mounting screws	15-16	ft-lb
Torque	Nozzle cap nut	50-55	ft-lb
Torque	Oil filter	Hand tight plus 1/4 to 1/2 turn
Torque	Rear bearing plate	40-45	ft-lb
Torque	Rocker arm nut	4-10	ft-lb	Friction between threads only; used to adjust valve lash
Torque	Rocker arm stud	35-40	ft-lb
Torque	Rocker-box cover	8-10	ft-lb
Valve clearance	Exhaust valve clearance (cold)	.017	inch	cold
Valve clearance	Intake valve clearance (cold)	.017	inch	cold
Voltage	Solenoid voltage drop	0.3	V	maximum
Voltage	Starter circuit voltage drop (battery ground to block; battery positive to solenoid)	0.6	V	maximum each
Voltage	Starter frame voltage drop	0.3	V	maximum

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
Coolant	50-50 mix ethylene glycol anti-freeze and water				Complete change every year; rust inhibitors prevent corrosion
Engine oil	Multi-grade such as 5W-30		below 0°C		Recommended for ambient temperatures of 32 F and colder
Engine oil	SAE 10W below 30 F; SAE 30 above 30 F				From nameplate oil recommendation
Engine oil	SAE 15W-40 or 20W-40	API CD/SE	-10°C to 32°C	6.5 U.S. quarts	Includes filter; CD/SE all viscosity grades, CC/SE only for 10W-30, 10W-40, 5W-30
Fuel	ASTM 2-D or 1-D diesel fuel	Minimum Cetane number 45			Use ASTM 1-D below 32 F, during long light-load or no-load periods

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

Procedures

Adjusting Injection Nozzle Opening Pressure adjustment

⚠ Do not adjust pressure without a testing fixture.

Tools: Diesel Nozzle Tester 420-0184

Remove nozzle from the engine.
Remove plug from center of cap nut and loosen cap nut.
Install nozzle on a static fuel nozzle testing fixture.
Adjust opening pressure to 1750 psi by turning adjusting screw.
Clockwise increases pressure, counterclockwise decreases it.

Adjusting Valve Clearance adjustment

⚠ Four-cylinder engines do not have a BC mark on the flywheel.

Tools: Feeler gauge

Rotate flywheel clockwise until No.1 cylinder is on compression stroke at TC mark.
Turn 10-45 degrees past TC.
Check clearance between rocker arm and valve with feeler gauge.
Adjust with lock nut securing rocker arm.
Turn flywheel 180 degrees for No.2, then No.4, then No.3 cylinder, adjusting each.

Testing Thermostat diagnostic

Tools: Thermometer

Remove thermostat from cylinder head.
Heat a pan of water to approximately 150 F.
Suspend thermostat in water; it should start to open.
Remove from hot water and allow to cool; it should close in a short time.
Replace if it sticks or does not operate properly.
Always install a new gasket when replacing the thermostat.

Flushing Cooling System maintenance

Tools: Flushing gun

Drain radiator, cylinder block and exhaust manifold.
Remove inlet and outlet hoses between engine and radiator.
Close all drain plugs; attach flushing gun nozzle to water outlet.
Restrict inlet opening until system fills with water, then apply air pressure gradually.
Repeat until water from cylinder block flows clean.
Remove flushing gun.
Reinstall thermostats, hoses and drain plugs; refill with proper coolant.
Check system for leaks.

Oil Filter Change maintenance

Tools: Filter wrench

Place pan under old filter and remove by turning counterclockwise.
Clean filter mounting area.
Lubricate gasket on new filter with oil.
Screw filter on clockwise until gasket touches mounting base.
Tighten 1/2 turn.

Out-of-Service Protection (over 30 days) maintenance

⚠ Starter cranking is too fast; oil or inhibitor fluid will fire if cranked with starter.

Run engine until thoroughly warm under at least 50 percent load.
Shut down and drain oil base while warm; refill.
Remove glow plugs, pour 1 ounce rust inhibitor into each cylinder, install glow plugs.
Crank engine by hand only to distribute oil.
Service air cleaner per Maintenance Schedule.
Clean throttle and governor linkage; wrap with clean cloth.
Plug exhaust outlets.
Disconnect battery and follow standard storage procedure.

Returning a Unit to Service maintenance

⚠ Do not smoke while servicing batteries.

Remove cover and protective wrapping; remove plug from exhaust outlet.
Check warning tag on oil base and verify oil viscosity.
Clean and check battery; measure specific gravity.
Check fuel injectors and fuel lines are secure and correctly torqued.
Clean radiator.
Connect batteries.
Verify no loads are connected to engine.
Start engine.

Bleeding Fuel System operation

⚠ Return priming lever inward (disengaged position) to permit normal pump operation.

Disconnect fuel return line.
Operate hand priming lever on fuel transfer pump.
Continue until fuel flowing from return line is free of air bubbles.
Reconnect the fuel return line.
If camshaft pump lobe is up, crank engine one revolution to permit hand priming.

Break-In Procedure operation

⚠ Continuous running under one half load during first few hundred hours may cause poor ring seating.

Run one half hour at 1/2 load.
Run one half hour at 3/4 load.
Run at full load.
Drain and replace crankcase oil after first 50 hours; drain while still hot.

Preheating and Starting operation

⚠ Do not exceed the one minute preheat periods.

⚠ Do not use ether as a cold weather starting aid.

Engage PREHEAT switch 30 seconds if above 55 F, 60 seconds if below 55 F.
Engage START switch while continuing preheat.
Hold until engine comes up to speed.
If engine fails to start in 15-20 seconds, repeat preheat and start.
Verify oil pressure gauge reads at least 20 psi.

Stopping the Engine operation

Push fuel solenoid switch to stop position.
Release switch when set stops.
If stop circuit fails, close fuel valve.

Fuel Transfer Pump Removal and Disassembly repair

⚠ Do not pry the cover and body apart; this would damage the diaphragm.

Tools: Screwdriver, File

Remove pump inlet and outlet lines.
Remove two cap screws holding pump to engine and lift off.
Notch cover and body with a file; remove six screws.
Tap body with a screwdriver to separate the two parts.
Drive out rocker arm hinge pin.
Remove rocker arm, spring and link.
Lift out diaphragm assembly and diaphragm spring.

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

What is the oil capacity of the Cummins/Onan RDJF?

The Cummins/Onan RDJF engine has an oil capacity of 6.15 liters.

What is the displacement of the Cummins/Onan RDJF?

The Cummins/Onan RDJF has a displacement of 2.3 liters with 4 cylinders.

Which generators use the Cummins/Onan RDJF engine?

The Cummins/Onan RDJF powers 2 generator set(s), including Cummins/Onan 17.5RDJF-3CR, Cummins/Onan 20W-20.

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

A commonly reported issue on generators using the Cummins/Onan RDJF is: Engine fails to start — little or no fuel flow from return line. Cause: Fuel supply system problem. Fix: Check fuel supply system: fuel tank empty?; shutoff valves closed?; fuel lines kinked?; loose connections?; clogged fuel filters?.