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Cummins/Onan VT-28-G Engine

The Cummins/Onan VT-28-G is an engine rated at 1800 rpm. It powers generator sets from Cummins/Onan, including the 450 DFW. It holds 102 L (107.8 US qt) of oil and 161 L (42.5 gal) of coolant.

Also known as: Cummins VT-28-G

1800 rpm

Rated speed

102.0 L

Oil capacity

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

Engine specifications

Oil capacity	102 L (107.8 US qt)
Coolant capacity	161.0 L
Rated speed	1800 rpm

Generator sets powered by this engine

Cummins/Onan 450 DFW

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

Common problems

Engine will not crank
Cause: Fault lamp on
Fix: Correct fault and reset control.
The FAULT 1 or FAULT 2 fault lamp lights. Engine shuts down immediately, engine runs for several seconds and then shuts down, or engine continues to run FAULT 1
Cause: The standard undesignated fault functions are programmed to shut down the set when a fault is sensed. Fault 1 is timed delayed while Fault 2 is immediate. The nature of the fault is an optional selection that is determined when the set installation is designed. The undesignated fault functions may also be programmed for non-shutdown or non-time delay.
SWITCH OFF lamp flashes
Cause: Run/Stop/Remote switch is in the Stop position which will prevent automatic starting if an automatic transfer switch is used
Fix: Move the Run/Stop/Remote switch to the Remote position for automatic starting.
Starter has been locked out because of excessive cranking time. OVERCRANK
PRE LO OIL PRES lamp lights. Engine continues to operate
Cause: Engine oil pressure has dropped to 20 psi (138 kPa)
Fix: If generator is powering critical loads and cannot be shut down, wait until next shutdown period and then follow step 5 procedure. If engine can be stopped, follow procedures in step 5.
PRE HI ENGINE TEMP lamp lights. Engine continues to operate
Cause: Engine has begun to overheat and engine temperature has risen to approximately 205°F (97°C)
Fix: If generator is powering non-critical and critical loads and cannot be shutdown, use the following: Reduce load if possible by turning off non-critical loads; Check air inlets and outlets and remove any obstructions to airflow; Open doors or windows in generator area to increase ventilation. If engine can be stopped, follow procedure in step 3.
OVERCRANK lamp lights and engine stops cranking, or Engine runs, shuts down, and LO OIL PRES lamp lights
Cause: Possible fuel system problem
Fix: Check for empty fuel tank, fuel leaks, or plugged fuel lines and correct as required; Check for dirty fuel filter and replace if necessary (see MAINTENANCE section); Check for dirty or plugged air filter and replace if necessary (see MAINTENANCE section); Refer to Step 5; Reset the control and restart after correcting the problem. Contact an Onan Dealer or Distributor for service if none of the above.
No AC output voltage
Cause: Field breaker is tripped
Fix: Reset breaker. Contact an Onan Dealer or Distributor if voltage build up causes breaker to trip.
LO OIL PRES lamp lights. Engine shuts down
Cause: Engine oil pressure has dropped to 14 psi (97 kPa)
Fix: Check oil level, lines and filters. If oil system is okay but oil level is low, replenish. Reset control and restart. Contact an Onan Dealer or Distributor if oil pressure is not in the range of 50 to 70 psi (345 to 483 kPa).
LO FUEL lamp lights. Engine shuts down and LO OIL PRES lamp lights
Cause: Engine has run out of fuel
Fix: Check fuel level and replenish as required.
LO FUEL lamp lights. Engine continues to run
Cause: Diesel fuel supply is running low
Fix: Check fuel supply and replenish as required.
LO ENG TEMP lamp lights. Set is in standby mode but is not operating. (Lamp lights when engine coolant temperature is 70°F (21°C) or lower. Since the lamp goes out after the engine warms up, there should be no cause for alarm even during initial generator set operation.)
Cause: Engine coolant heater is not operating or is not circulating coolant
Fix: Check for the following conditions: Coolant heater not connected to power supply. Check for blown fuse or disconnected heater cord and correct as required; Check for low coolant level and replenish if required. Look for possible coolant leakage points and repair as required; Contact an Onan Dealer or Distributor if none of the above.
HI ENG TEMP lamp lights. Engine shuts down
Cause: Engine has overheated (engine temperature has risen above 215°F/102°C) or coolant level is low (sets with coolant level sensor)
Fix: Allow engine to cool down completely before proceeding with the following checks: Check coolant level and replenish if low. Look for possible coolant leakage points and repair if necessary; Check for obstructions to cooling airflow and correct as necessary; Check for a slipping fan belt and tighten if loose; Reset control and restart after locating and correcting problem. Contact an Onan Dealer or Distributor if none of the above.
Green RUN lamp lights following engine start-up
Fix: Indicates all engine systems are normal. No corrective action required.
Green RUN lamp does not light following engine start-up
Cause: Possible Start/Disconnect relay failure
Fix: Contact an Onan Dealer or Distributor for assistance.

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan VT-28-G.

Service intervals

Item	Action	Hours	Months	Notes
Crankcase oil (new generator sets)	Drain	50 hr		First service — Drain and replace the crankcase oil after the first 50 hours of operation on new generator sets
Generator bearing	Inspect	1000 hr		Have bearing inspected for wear every 1000 hours by an Onan Distributor
Generator bearing (prime power)	Replace	10000 hr		For prime power, replace at least every 10,000 hours or after two years
Generator bearing (standby power)	Replace		60 mo	For standby power, replace at least every five years

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	Air cleaner nozzle distance from element	1	inch	25 mm minimum
Clearance	Exhaust pipe to combustible wall/partition clearance	12	inches
Clearance	Exhaust thimble inner sleeve minimum	9	inches
Other	Battery charging alternator maximum charge rate	35	amperes
Pressure	Air cleaner cleaning air pressure	30	psi	207 kPa; DFW, DFY and DFZ
Pressure	Crankcase breather drying air pressure	30	psi	maximum (OSHA)
Pressure	Engine oil pressure	345 to 483	kPa	engine at operating temperature
Pressure	Engine oil pressure	50 to 70	psi	engine at operating temperature
Pressure	Exhaust backpressure (maximum allowable)	3	inches Hg
Pressure	Exhaust backpressure (maximum allowable)	41	inches H2O
Pressure	External prime pressure (cranking)	103	kPa	for 15 seconds
Pressure	External prime pressure (cranking)	15	psi	for 15 seconds
Pressure	Low oil pressure shutdown setpoint	14	psi	97 kPa; time delayed about 10 seconds following starter disconnect
Pressure	Lubrication priming pressure	207	kPa
Pressure	Lubrication priming pressure	30	psi
Pressure	Normal engine oil pressure range	50 to 70	psi	345 to 483 kPa
Pressure	Pre-low oil pressure alarm (optional 12-lamp system)	20	psi	137 kPa or less
Pressure	Radiator air discharge static pressure	0.25	inch H2O	0.018 inch Hg; 450 DM, 500 DM, 600 DFY, 750 DFZ
Pressure	Radiator air discharge static pressure	0.5	inch H2O	0.037 inch Hg; 450 DFW
Resistance	Battery specific gravity (recharge below)	1.260	specific gravity	use a hydrometer
Speed	Cycle cranking option	15	seconds	three 15-second cranking cycles with two 15-second rest periods
Speed	Fine speed adjustment range (SPEED ADJUST potentiometer)	±100	RPM	less than
Speed	Frequency meter speed relation	30	r/min	each hertz equals 30 r/min
Speed	No-load governed speed, 50 Hz 3% droop	1545	RPM	51.5 Hz
Speed	No-load governed speed, 50 Hz 5% droop	1575	RPM	52.5 Hz
Speed	No-load governed speed, 50 Hz isochronous	1500	RPM	50.0 Hz
Speed	No-load governed speed, 60 Hz 3% droop	1854	RPM	61.8 Hz
Speed	No-load governed speed, 60 Hz 5% droop	1890	RPM	63.0 Hz
Speed	No-load governed speed, 60 Hz isochronous	1800	RPM	60.0 Hz
Speed	Overcrank cranking limit (standard control)	75	seconds	starter disengages after 75 seconds of cranking
Speed	Overspeed shutdown, 50 Hz units	1850 ± 50	r/min
Speed	Overspeed shutdown, 60 Hz units	2100 ± 90	r/min
Speed	Starter disconnect speed	450 to 570	r/min
Temperature	Engine water temperature	165 to 195	°F	depending on load and ambient temperature
Temperature	Engine water temperature	74 to 91	°C	depending on load and ambient temperature
Temperature	Heat exchanger room temperature differential	11 to 17	°C
Temperature	Heat exchanger room temperature differential	20 to 30	°F
Temperature	High engine temperature shutdown	215	°F	102°C; time delayed about 10 seconds following starter disconnect
Temperature	LO ENG TEMP lamp setpoint	70	°F	21°C or lower engine water jacket temperature
Temperature	Pre-high engine temperature alarm	205	°F	97°C; optional 12-lamp system
Torque	Oil drain plug	60-70	ft.lb	also 81-95 N·m
Torque	Oil filter housing plug	15 to 20	ft. lb.
Torque	Oil filter housing plug	20 to 27	N·m
Voltage	Electrical system starting voltage	24	Volts DC
Voltage	Random voltage variation	±1	%	constant loads
Voltage	Rating condition, ambient temperature	77	°F	25°C; also altitude 300 feet (92 m)
Voltage	Voltage adjust rheostat range	±5	%	optional; of rated output voltage
Voltage	Voltage regulation, VRAS-2 regulator	±2	%	from no load to full load

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	Notes
Coolant	Ethylene glycol base permanent antifreeze (or plain water)			Use flexible coolant lines with heat exchanger or remote mounted radiator. Do not use antifreeze with an anti-leak (stop leak) formula; it can prevent coolant flow through the filter.
Coolant	Water or water/antifreeze mixture with DCA precharge	Water clean, low in mineral content, free of chloride, sulphate, or acid; permanent type antifreeze		New engines shipped with precharge water filter; precharge water filter compatible with plain water and all permanent antifreezes except methoxy propanol base; do not use antifreeze with anti-leak additives; capacities (standard radiator): 44 gallons (166 litres) 450 DM, 500 DM, 600 DFY; 42.5 gallons (161 litres) 450 DFW; 55 gallons (208 litres) 750 DFZ
Engine oil	SAE 5W synthetic	API class CC/CD; sulphated ash not exceeding 1.85 percent; pour point 9°F (5°C) below lowest expected temperature; viscosity 10,000 mPa*s max at -31°F (-35°C) and 4.1 mm2/s min at 212°F (100°C)	below -25°C	For ambient temperatures consistently below -13°F (-25°C) with no provision to keep engine warm; do not use petroleum base 5W grade oil
Engine oil	SAE 10W-30	API Class CC/CD, maximum sulphated ash 1.85 percent	-25°C to 35°C	-13°F to 95°F; capacities: 22.3 Gallons (84 litres) 450 DM, 500 DM, 600 DFY; 27 Gallons (102 litres) 450 DFW; 34 Gallons (129 litres) 750 DFZ (filters, lines and crankcase)
Engine oil	SAE 15W-40	API Class CC/CD	above -10°C	14°F (-10°C) and above
Engine oil	SAE 20W-40	API Class CC/CD	above 0°C	32°F (0°C) and above
Fuel	No. 2 Diesel	ASTM		Cummins engines on DF series normally use ASTM No. 2 Diesel fuel; will operate on diesel fuels within the specifications in the Cummins engine manual. Never use galvanized fuel lines or fittings.
Fuel	No. 2 diesel			Engine primarily designed for No. 2 diesel fuels; will also operate on No. 1 fuel or similar if specifications met; filter or strain fuel as tank is filled
Grease	non-conductive grease			Light coating on battery terminals to retard corrosion
Other	anti-seize compound			Use when reassembling threaded aluminum parts (coolant heater)

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

Procedures

Generator Voltage Adjust (Detector AC Option) adjustment

⚠ High voltages in the control present an electrical shock hazard which can cause severe personal injury or death.

Tools: Screwdriver, Wrench

Operate Phase Selector switch to read generator output current and voltage.
Insert a screwdriver into the Voltage Adjust R21 potentiometer on the control front; loosen the locking nut with a wrench.
While observing the voltmeter, slowly turn the screwdriver clockwise to increase or counterclockwise to decrease voltage; adjust to rated nameplate voltage.
Retighten the locking nut without changing the adjustment.
Operate Phase Selector switch to the Off position.

Generator Voltage Adjust (Without Detector AC Option) adjustment

⚠ High voltages in the control present an electrical shock hazard which can cause severe personal injury or death.

Tools: Screwdriver, Accurate 2% voltmeter

Open control panel doors, locate VRAS-2 (upper left), and locate terminal board TB1 and R82 potentiometer.
Connect an accurate 2% voltmeter to VRAS-2 terminal board TB1-2 and TB1-3 terminals.
While observing the voltmeter, insert a screwdriver into R82 potentiometer and slowly turn to increase or decrease voltage until adjusted to rated nameplate voltage.
Disconnect voltmeter from TB1 and close control panel doors.

Governor Gain Adjustment adjustment

Close main line circuit breaker and apply approximately 1/4 of rated load.
Make sure engine speed is constant.
Turn GAIN potentiometer clockwise slowly until engine speed is not constant.
Turn potentiometer counterclockwise until a constant speed is achieved.
Turn counterclockwise an additional 1/2 division.
Use SPEED ADJUST potentiometer for fine speed adjustments of less than ±100 RPM.

Governor Preliminary Adjustments adjustment

Turn idle speed potentiometer counterclockwise to its stop, then clockwise 10 turns.
Turn run speed potentiometer counterclockwise to its stop, then clockwise 10 turns.
Turn gain potentiometer fully counterclockwise.
Turn droop potentiometer fully counterclockwise for isochronous operation.
Turn droop screw to approximately 40 for 3 percent droop.
Turn droop screw to approximately 80 for 5 percent droop.

Voltage Regulator Adjustment adjustment

⚠ High voltages in the control present an electrical shock hazard which can cause severe personal injury or death.

Tools: Screwdriver, Wrench

Operate Phase Selector switch to read generator output current and voltage.
Insert a screwdriver into the Voltage Adjust R21 potentiometer on the control front; loosen the locking nut.
Turn screwdriver to set the adjustment screw to the mid-position and retighten the locking nut.
Open control panel doors, locate VRAS-2 (upper left), and locate R32 potentiometer.
While observing the voltmeter, insert a screwdriver into R32 potentiometer and slowly turn to increase or decrease voltage until adjusted to rated nameplate voltage.
Close control panel doors and operate Phase Selector switch to the Off position.

Battery Connection installation

⚠ Ignition of explosive battery gases can cause severe personal injury. Do not smoke while servicing batteries.

For DFW/DFY use two 12-volt batteries; for DFZ use four 12-volt batteries.
Connect two batteries in series (negative post of first battery to positive post of second).
Connect positive battery cables before connecting negative battery cables to prevent arcing.
Connect negative cable to a convenient bolt on the engine; connection must be clean and paint free.
If an automatic transfer switch without a built-in charge circuit is used, connect a separate trickle/float charger.

Air Cleaner Service (DFW, DFY) maintenance

⚠ Filters should be handled with care to prevent damage.

Tools: compressed air

Loosen the eight attaching bolts and lift off the air cleaner head.
Remove the air filter element from the filter housing.
Blow low pressure compressed air (30 psi/207 kPa) through element from the clean side.
Hold nozzle at least 1 inch (25 mm) away to avoid damaging the element.

Air Cleaner Service (DFZ) maintenance

Tools: compressed air

Unsnap four latches holding head, lift off head and remove filter element.
Remove and discard precleaner cartridge.
Blow low pressure compressed air through pleated paper cartridge from the inside.
Hold nozzle at least 1 inch (25 mm) away to avoid damaging the element.
Replace pleated paper cartridge at every fourth cleaning.

Coolant Filter Service maintenance

⚠ Do not use antifreeze with an anti-leak formula; the stop leak element can prevent or retard coolant flow through the filter.

Close the shutoff valve.
Unscrew the coolant filter and discard.
Apply a light coat of lubricating oil to the gasket surface.
Install new filter and tighten by hand until seal just touches filter head.
Tighten an additional one-half to three-fourths turn.
Open the shutoff valve.

Coolant Heater Service maintenance

⚠ Failure to remove AC power presents a shock hazard and can cause serious personal injury or death.

⚠ Contact with hot coolant can result in severe burns.

Remove AC power from coolant heater.
Allow heater to cool before proceeding.
Remove the head and valve assembly.
Clean any scale deposits out of the tank.
Remove heating element and scrape off any accumulated scale.
Restore AC power to heater after system has been filled with coolant.

Cooling System Flushing maintenance

⚠ Excessive air pressure while starting the water flow could split the radiator core. Apply air pressure gradually.

Tools: flushing gun, compressed air

Open upper and lower radiator hose connections and install the radiator cap.
Attach flushing gun nozzle to lower radiator hose connection and fill radiator with water.
Gradually apply air pressure to avoid damaging the core.
Shut off air and allow radiator to refill; repeat until water runs clean.
Remove thermostat to flush block; attach flushing gun to upper radiator hose.
Restrict lower hose opening until block fills; apply air pressure and force water out.
Replace thermostat and all hoses and refill cooling system.

Crankcase Breather Service (DFW, DFY) maintenance

Tools: compressed air

Remove wing nut, flat washer and rubber washer; lift cover away from filter assembly.
Lift out breather element, vapor element and gasket.
Clean all parts with approved solvent; dry with compressed air (30 psi maximum OSHA).
Inspect all parts, replace if necessary.
Reassemble filter assembly, replace cover and secure.

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

Voltage reconnection

Voltage	Phase	Connection	Leads	Notes
110/190	3			Voltage code 519, 50 Hz
115/200	3			Voltage code 519, 50 Hz
120/208	3			Voltage code 4, 60 Hz
120/240	3			Voltage code 5D, 60 Hz
127/220	3			Voltage code 521, 50 Hz
220/380	3			Voltage code 520, 50 Hz
230/400				50 Hz (as printed '230/400 8 50')
240/416	3			Voltage code 7X, 60 Hz
240/480	3			Voltage code 6D, 60 Hz
277/480	3			Voltage code 4X, 60 Hz
347/600	3			Voltage code 9X, 60 Hz
920/380	3			Voltage code 7, 60 Hz (as printed; possibly garbled)
954/440	3			50 Hz (as printed; possibly garbled)
higher nameplate	1	Delta	Any two line terminals (L1-L2, L1-L3, L2-L3)	Single phase at HIGHER nameplate voltage; terminal LO not used
higher nameplate	1	Wye (Series Wye)	Any two line terminals (L1-L2, L1-L3, L2-L3)	Single phase at HIGHER nameplate voltage; terminal LO not used
higher nameplate	3	Delta	L1, L2, L3	Three phase at HIGHER nameplate voltage; terminal LO not used
higher nameplate	3	Wye (Series Wye)	L1, L2, L3	Three phase at HIGHER nameplate voltage; terminal LO not used
lower nameplate	1	Delta	LO (neutral) + L1 or L2	Single phase at LOWER nameplate voltage; terminal LO can be grounded if required. Do not connect load wire to L3 at lower nameplate voltage.
lower nameplate	1	Wye (Series Wye)	LO (neutral) + one line terminal (L1, L2 or L3)	Single phase at LOWER nameplate voltage; terminal LO can be grounded 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.

Common questions

What is the oil capacity of the Cummins/Onan VT-28-G?

The Cummins/Onan VT-28-G engine has an oil capacity of 102 L (107.8 US qt).

Which generators use the Cummins/Onan VT-28-G engine?

The Cummins/Onan VT-28-G powers 1 generator set(s), including Cummins/Onan 450 DFW.

What is a common problem with the Cummins/Onan VT-28-G engine?

A commonly reported issue on generators using the Cummins/Onan VT-28-G is: Engine will not crank. Cause: Fault lamp on. Fix: Correct fault and reset control..