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Cummins/Onan 4B3.9-G Engine

The Cummins/Onan 4B3.9-G is a 3.92 L naturally aspirated engine rated at 1800 rpm, producing up to 36 kW. It powers generator sets from Cummins/Onan, including the 28DGBB, 30DGHC, 35 DGBB and 36 DGBC. It holds 11.5 L (3.0 gal) of oil and 21 L (5.5 gal) of coolant.

Also known as: 4B3.9G, Cummins 4B3.9-G

Part of the Cummins/Onan 4B3.9 engine family — 5 variants share parts & fitment.

3.92 L

Displacement

1800 rpm

Rated speed

36 kW

Gross power

11.5 L

Oil capacity

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

Engine specifications

Oil capacity	11.5 L
Coolant capacity	21.0 L
Displacement	3.92 L
Aspiration	naturally aspirated
Rated speed	1800 rpm
Gross power	36 kW

Generator sets powered by this engine

Cummins/Onan 28DGBB Cummins/Onan 30DGHC Cummins/Onan 35 DGBB Cummins/Onan 36 DGBC Cummins/Onan 40 DGBCCummins/Onan DTBACummins/Onan DXBA

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

Common problems

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 time 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: Indicates 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
No AC output voltage
Cause: Field breaker is tripped
Fix: Reset breaker; contact an authorized service center if voltage buildup causes breaker to trip
LO FUEL LAMP lights. Engine shuts down and LO OIL PRES lamp lights
Cause: Indicates engine has run out of fuel
Fix: Check fuel level and replenish as required
LO FUEL lamp lights. Engine continues to run
Cause: Indicates diesel fuel supply is running low
Fix: Check fuel supply and replenish as required
HI ENG TEMP lamp lights. Engine shuts down
Cause: Indicates engine has overheated (engine temperature has risen above 222°F/106°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 authorized service center for service if none of the above
Fault lamp lights but no fault exists. Engine gauges show oil pressure, engine temperature, and frequency (speed) are within normal limits
Cause: The monitor board or a sensor may be at fault
Fix: Contact an authorized service center for service
Engine will not crank
Cause: Indicates possible fault with control or starting system
Fix: Check for the following conditions: fault lamp on, correct fault and reset control; poor battery cable connections, clean the battery cable terminals and tighten all connections; discharged or defective battery, recharge or replace the battery; emergency stop button (if equipped) pushed in, to reset, pull switch out and move Run/Stop/Remote switch to Stop position, then push test switch to Reset/Lamp position; contact an authorized service center if none of the above
Engine runs and then shuts down, OVERSPEED lamp lights
Cause: Indicates engine has exceeded normal operating speed
Fix: Contact an authorized service center for service
PRE LO OIL PRES lamp lights. Engine continues to operate
Cause: Indicates 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: Indicates engine has begun to overheat and engine temperature has risen to approximately 215°F (102°C)
Fix: If generator is powering non-critical and critical loads and cannot be shut down, reduce load if possible by turning off non-critical loads; check air inlets and outlets and remove any obstructions to airflow; 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: Indicates 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); reset the control and restart after correcting the problem; contact an authorized service center for service if none of the above
LO OIL PRES lamp lights. Engine shuts down
Cause: Indicates engine oil pressure has dropped to 14 psi (97 kPa)
Fix: Check oil level, lines and filters; if oil system is OK but oil level is low, replenish; reset control and restart; contact an authorized service center if oil pressure is not in the range of 25 to 40 psi (172 to 275 kPa)
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: Indicates 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 authorized service center for service if none of the above
Green RUN lamp lights following engine startup
Cause: Indicates all engine systems are normal
Fix: No corrective action required

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan 4B3.9-G.

Maintenance schedule

Item	Spec	Part #	Interval
Air filter		—	250 hr
Fuel filter	Spin-on paper element fuel filters	—
Oil filter	Spin-on full flow lube oil filter	—
Battery		—	180 hr
Belt		—	250 hr
Coolant		—
Coolant filter		—
Oil	Change the oil and filter at the intervals recommended in the Maintenance Table.	—
Spark plug	Spark plugs	—

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	Months	Notes
Вентиляционные устройства генератора	Check	10 hr		10 часов / еженедельно
Весь агрегат	Test	10 hr		Включение минимум на час, предпочтительно с нагрузкой 50 %; 10 часов / еженедельно
Подключение вспомогательной клеммной коробки	Check	10 hr		10 часов / еженедельно
Уровень охладителя воды	Check	10 hr		10 часов / еженедельно
Уровень смазочного масла в двигателе	Check	10 hr		10 часов / еженедельно
Уровень топлива	Check	10 hr		10 часов / еженедельно
Уровень электролита в батарее	Check	10 hr		10 часов / еженедельно
Crankcase oil	Change	50 hr		First service — Drain and replace the crankcase oil after the first 50 hours of operation on new generator sets (break-in)
Вентиляционный клапан топливного бака	Check	100 hr		100 часов / ежемесячно (положение отметки в таблице)
Все переключатели (в т.ч. двигателя)	Test	100 hr		100 часов / ежемесячно
Осадок в топливном баке	Drain	100 hr		100 часов / ежемесячно (положение отметки в таблице)
Отверстие и внутреннее пространство генератора	Clean	100 hr		Очистка сухим воздухом; 100 часов / ежемесячно
Соленоид подачи топлива	Check	100 hr		100 часов / ежемесячно
Уровень зарядки батареи гидрометром	Test	100 hr		100 часов / ежемесячно
Воздушный фильтр (у масляного – уровень масла)	Check	200 hr		200 часов / ежегодно
Все болты и гайки	Check	200 hr		Проверка и затягивание при необходимости; 200 часов / ежегодно
Все реле распределительной аппаратуры	Test	200 hr		200 часов / ежегодно
Кабельные контакты батареи	Clean	200 hr		200 часов / ежегодно; зачистка и смазка
Линии топлива, воздуха и выхлопная система на протечки	Check	200 hr		200 часов / ежегодно
Натяжение клиновидного ремня	Check	200 hr		200 часов / ежегодно
Плавкие предохранители и отключающие устройства	Check	200 hr		200 часов / ежегодно
Подшипники генератора	Lubricate	200 hr		200 часов / ежегодно
Проверка агрегата изготовителем	Inspect	200 hr		200 часов / ежегодно
Противовибрационные устройства	Check	200 hr		При наличии таковых; 200 часов / ежегодно
Смазочное масло	Change	200 hr		200 часов / ежегодно
Чистка всего агрегата и наружной поверхности панели управления	Clean	200 hr		200 часов / ежегодно
Чистота контакторов и контактов прерывателей	Check	200 hr		200 часов / ежегодно
Valve lash	Adjust	1000 hr		Footnote 5: Contact an authorized service center for service.
Alternator bearings (sealed)	Inspect	4000 hr		Inspect all sealed bearings every 4000 to 4500 hours (10000 hr/2 years)
Alternator bearings (sealed)	Replace	30000 hr		Replace all sealed bearings every 30000 hr/5 years (or if necessary after 10000 hr/2 years)
Содержание антифриза в системе охлаждения и фильтр	Check		6 mo	В таблице указано «Раз в 6 месяцев»

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
Other	Alternator cooling air flow	41.3	m3/min
Other	Alternator excitation current - full load	2.2	amps
Other	Alternator excitation current - no load	0.5	amps
Other	Automatic stop delay after normal power source returns	about 15 minutes	minutes
Other	Combustion air flow - standby	20.9	m3/min	standby rating
Other	Coolant level below radiator cap opening	about two inches (50 mm)	mm	cold engine
Other	Cooling system air flow	248	m3/min	standard set-mounted radiator
Other	Cycle cranking - number of starting cycles	1 to 7	cycles
Other	Exercise period	at least once a week for a minimum of 30 minutes with load	minutes
Other	Exhaust flow at set rated load - standby	33.3	m3/min	standby rating
Other	Fault current regulation (max output current on any phase under fault)	3	times rated current	single and three phase faults
Other	Full load acceptance - frequency dip / recovery time	12.6% / 3.7	% / seconds	NFPA 110 single step load
Other	Full load acceptance - voltage dip / recovery time	29.1% / 3.2	% / seconds	NFPA 110 single step load
Other	Full load rejection - frequency rise / recovery time	3.9% / 2.9	% / seconds	load rejection
Other	Full load rejection - voltage rise / recovery time	18.4% / 1.5	% / seconds	load rejection
Other	Ground fault warning (optional) sensing range	100-1200	amps, time delay 0-1 s	600 VAC class, solid ground
Other	Maximum air cleaner restriction with clean filter	3.7	kPa
Other	Maximum surge power	233	kW	PTS test
Other	Motor starting kVA at 90% sustained voltage - PMG excitation	920	kVA	PTS test
Other	Motor starting kVA at 90% sustained voltage - shunt excitation	770	kVA	PTS test
Other	Over current shutdown (51)	>110 and <175	% of rating
Other	Over current warning	>110 for >60 s, or >400 for >1 s	% of rating
Other	Over frequency shutdown/warning (81o)	0-10	Hz above nominal, 0-20 s time delay	default disabled
Other	Over load (kW) warning default	105	% of rated kW, 60 s delay	range 50-140%, 0-120 s
Other	Power rating reference conditions	altitude 300 feet (92 m), ambient temperature 81 F (27 C)
Other	Reverse Var shutdown default	0.2	per unit, 10 s delay	threshold 0.15-0.50, delay 10-60 s
Other	Reverse power shutdown (32) default	10	% of standby kW rating, 3 s delay	range 5-20%, delay 1-15 s
Other	Short circuit shutdown	>175	% of rating
Other	Time delay start	0-300	seconds	default 0 s
Other	Time delay stop (cool down)	0-600	seconds	default 0 s
Other	Total heat rejection - standby	7.8	MJ/min	standby rating
Other	Under frequency shutdown (81u) default	6	Hz below nominal, 10 s time delay	adjustable 0-10 Hz, 0-20 s
Other	Глубина фундамента/цоколя и выступ за пределы агрегата	не менее 150	мм (6 дюймов)
Other	Минимальное расстояние от генератора до стены, резервуара или панели в машинном зале	1	м
Other	Нагрузка на грунт (ННГ) от агрегата, охладителя, топлива и фундамента	менее 9800	кг/м2 (2000 фунтов на кв. фут) или 96 кПа	требует проверки по местным нормам
Other	Площадь впускного отверстия воздуха для агрегатов с радиаторным охлаждением	в 1,5-2 раза больше площади радиатора
Other	Просвет выхлопной трубы глушителя	12	дюйма (300 мм)	двигатель QSK60
Other	Просвет выхлопной трубы глушителя	3	дюйма (76 мм)	двигатели B3.3, 4B, 6B
Other	Просвет выхлопной трубы глушителя	4	дюйма (100 мм)	двигатель 6C
Other	Просвет выхлопной трубы глушителя	6	дюйма (152 мм)	двигатели L, N, K19, V28
Other	Просвет выхлопной трубы глушителя	6×2	дюйма (152 мм)	двигатели K38, QSK30
Other	Просвет выхлопной трубы глушителя	8	дюйма (200 мм)	двигатели K50, QSK15
Other	Прочность бетона фундамента на сжатие (28 суток)	не менее 17200	кПа (2500 фунтов на кв. дюйм)
Pressure	BMEP at set rated load - prime	1816	kPa	prime rating
Pressure	BMEP at set rated load - standby	1979	kPa	standby rating
Pressure	Engine oil pressure	25 to 45	psi	engine at operating temperature
Pressure	Low oil pressure shutdown	14 psi (97 kPA)	psi
Pressure	Maximum allowable exhaust back pressure	41	inches H2O
Pressure	Maximum exhaust back pressure	10.2	kPa
Pressure	Maximum fuel inlet restriction	152.4	mm Hg
Pressure	Maximum fuel return restriction	254.0	mm Hg
Pressure	Normal engine oil pressure range	25 to 40 psi (172 to 275 kPa)	psi
Pressure	Pre-low oil pressure alarm	20 psi (137 kPA) or less	psi
Pressure	Предел обратного давления в выхлопной системе (большинство агрегатов Cummins)	3	дюйма рт. ст. (76 мм рт. ст.)	у последних моделей при максимальном потоке снижено до 2 дюймов рт. ст. (50 мм рт. ст.)
Resistance	Alternator rotor resistance	2.0	ohms	at 20 deg C
Resistance	Alternator stator resistance	0.0128	ohms per phase	at 20 deg C
Resistance	Battery specific gravity (recharge threshold)	recharge if below 1.260	specific gravity
Resistance	Сопротивление электрода заземления при глухом занулении генераторной установки	не более 20	Ом	рекомендуется, независимо от системы защиты
Speed	Alternator maximum speed	2250	rpm
Speed	Cycle cranking (optional)	three 15-second cranking cycles with two 15-second rest periods	seconds

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	water/antifreeze mixture			21.0 litres	Capacity with standard radiator 5.5 gallons (21 litres) for 37 DGBA, 35 DGBB, 40 DGBC, 50 DGCA, 60 DGCB; 6.5 gallons (25 litres) for 80 DGDA, 100 DGDB. Do not use antifreeze with anti-leak additives.
Coolant	Смесь воды и антифриза 50/50; низкосиликатный антифриз	Добавка Cummins DCA4 или эквивалент			Вода чистая, без хлоридов, сульфатов и кислот, с pH от 8,5 до 10,5; при заполнении холодной системы остается 6 (максимум 8) % дополнительной емкости для расширения
Engine oil	SAE 5W synthetic	API class CC/CD; sulphated ash content does not exceed 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 -23°C		For ambient temperature consistently below -10 F (-23 C) with no provision to keep engine warm; do not use petroleum base 5W grade oil
Engine oil	SAE 10W30 / SAE 15W40 / SAE 20W40 (spec table)		-25°C to 35°C	11.0 litres	Specifications table: Oil Capacity with Filters 11.5 quarts (11 litres) for 37 DGBA, 35 DGBB, 40 DGBC, 50 DGCA, 60 DGCB; 17.3 quarts (16 litres) for 80 DGDA, 100 DGDB. Oil type -13 F to 95 F (-25 C to 35 C) SAE 10W30; 14 F (-10 C) and above SAE 15W40; 32 F (0 C) and above SAE 20W40
Engine oil	SAE 10W-30	API Class CC/CD (max sulphated ash 1.85 percent)	-23°C to -10°C		-10 F (-23 C) to 14 F (-10 C)
Engine oil	SAE 15W-40	API Class CC/CD (max sulphated ash 1.85 percent)	above -10°C		14 F (-10 C) and above
Engine oil	SAE 20W-40	API Class CC/CD (max sulphated ash 1.85 percent)	above 0°C		32 F (0 C) and above
Fuel	ASTM No. 2 Diesel	ASTM No. 2			Cummins engines on DG series sets normally use ASTM No. 2 Diesel; will operate on alternate diesel fuels within engine manual specifications. Never use galvanized or copper fuel lines, fittings or tanks.
Fuel	No. 2 diesel fuel				Engine will also operate on No. 1 fuel or other similar fuels; consult engine manufacturer for specific requirements
Fuel	Дизельное топливо класса А1 или А2	BS 2869: Часть 1:1998 (класс А1); BS 2869: Часть 2:1998 (классы А2, С1, С2, D, E, F, G, H)			Топливо должно быть как можно более чистым, по возможности не содержать воды и загрязнений
Other	Природный газ	Наименьшая теплопроизводительность >30 МДж/Н·м3; плотность 0,7-0,9 кг/м3; метановое число >52; H2S >0,01 %; максимальная температура газа 50 °C	below 50°C		Требования к качеству газа для газовых двигателей; при несоответствии двигатель должен быть отключен

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

Fault codes

Code	Name	Meaning	Severity	Action
27	Low AC voltage shutdown	Voltage on any phase has dropped below a preset value; adjustable 50-95% of reference voltage, time delay 2-10 s.	Shutdown	Default 85% for 10 seconds; function tracks reference voltage.
32	Reverse power shutdown	Adjustment range 5-20% of standby kW rating, delay 1-15 seconds.	Shutdown	Defaults 10%, 3 seconds.
51	Over current shutdown	Output current on any phase more than 110%, less than 175% of rating and approaching thermal damage point of alternator.	Shutdown	Control includes algorithms to protect alternator from repeated over current conditions over a short period.
59	High AC voltage shutdown	Output voltage on any phase exceeds preset values; time to trip inversely proportional to amount above threshold. Adjustable 105-125% of nominal, time delay 0.25-10 s.	Shutdown	Default 110% for 10 seconds.
81o	Over frequency shutdown/warning	Adjustable 0-10 Hz above nominal frequency, time delay 0-20 seconds.		Defaults: disabled.
81u	Under frequency shutdown	Generator set output frequency cannot be maintained; adjustable 0-10 Hz below nominal governor set point, 0-20 s delay.	Shutdown	Default 6 Hz, 10 seconds.
-	Reverse Var shutdown	Shutdown level adjustable: threshold 0.15-0.50 per unit, delay 10-60 seconds.	Shutdown	Defaults 0.20, 10 seconds.
FAULT 1	FAULT 1 (red) lamp	Indicates an undedicated fault. May be field programmed as a shutdown or non-shutdown, and as a timed or non-timed fault (normally set for timed shutdown).	Shutdown	Determined when the set installation is designed.
FAULT 2	FAULT 2 (red) lamp	Indicates same features as Fault 1 (normally set for timed shutdown).	Shutdown	Determined when the set installation is designed.
HI ENG TEMP	HI ENG TEMP (red) lamp	Indicates engine has shut down because of critically high engine temperature (above 222 F/106 C) or low coolant level.	Shutdown	Allow engine to cool; check coolant level and replenish; check for cooling airflow obstructions; check fan belt; reset control and restart.
LO FUEL	LO FUEL (yellow) lamp	Indicates fuel supply is marginally low.	Warning	Check fuel supply and replenish as required.
LO OIL PRES	LO OIL PRES (red) lamp	Indicates engine has shut down because of critically low oil pressure (below 14 psi/97 kPa).	Shutdown	Check oil level, lines and filters; replenish oil if low; reset control and restart; contact an authorized service center if oil pressure is not in the range of 25 to 40 psi (172 to 275 kPa).
LOW ENG TEMP	LOW ENG TEMP (yellow) lamp	Lights if engine temperature is marginally low for starting (70 F/21 C or lower); may indicate an inoperative coolant heater.	Warning	Check coolant heater power supply, fuse and heater cord; check coolant level and replenish.
OVERCRANK	OVERCRANK (red) lamp	Indicates engine has failed to start during the cranking period.	Shutdown	Check for empty fuel tank, fuel leaks or plugged fuel lines; check for dirty fuel or air filter and replace if necessary; reset control and restart.
OVERSPEED	OVERSPEED (red) lamp	Indicates engine has shut down because of excessive speed.	Shutdown	Contact an authorized service center for service.
PRE HI ENG TEMP	PRE HI ENG TEMP (yellow) lamp	Indicates engine temperature is marginally high (approximately 215 F/102 C) and engine continues to operate.	Warning	Reduce load if possible; check air inlets and outlets and remove obstructions to airflow.
PRE LO OIL PRES	PRE LO OIL PRES (yellow) lamp	Indicates engine oil pressure is marginally low (20 psi/137 kPa or less) and engine continues to operate.	Warning	Find and correct the cause as soon as possible.
RUN	RUN (green) lamp	Comes on when starter circuit opens after set starting.	Info
SWITCH OFF	SWITCH OFF (flashing red) lamp	Indicates generator set is not in automatic start mode.	Warning	Move the Run/Stop/Remote switch to the Remote position for automatic starting.

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

Procedures

Vibration Isolators Installation and Adjustment Procedure installation

Place the vibration isolators on the genset support structure.
Shim or grout isolators so all bases are within 0.25 inch (6 mm) elevation of each other on a flat surface.
Loosen the side snubber lock nuts so the top plate is free to move vertically and horizontally.
Place the genset onto the isolators, aligning the skid mounting with the threaded isolator hole.
Adjust isolators with the leveling bolt through the skid (locking nut threaded up toward bolt head) to level the set.
Set nominal clearance between top plate and isolator base of 0.25 inch (6 mm) or greater.
Adjust leveling bolts until set is level and sufficient clearance remains, then lock with the lock nut.
Snubber nuts may remain loose to provide better isolation between genset and support structure.

Установка и подключение аккумуляторной системы installation

⚠ При зарядке батарей выделяются взрывоопасные газы – обеспечьте вентиляцию, вдали от искр и открытого огня.

⚠ Перед подключением батарей переключатель Run/Off/Auto на панели управления должен находиться в положении Off (ВЫКЛ).

⚠ Не устанавливайте кислотные батареи в одном помещении с никель-кадмиевыми.

Tools: Торцевой гаечный ключ

Установите батареи в чистое, хорошо освещенное и вентилируемое место с легким доступом для обслуживания.
Подключайте землю ПОСЛЕДНЕЙ, а при извлечении батареи отключайте ее ПЕРВОЙ.
Вначале подключайте ПЛЮСОВОЙ кабель генератора, затем минусовой; соблюдайте полярность.
Тщательно затяните гайки межъячеечных соединений и смажьте контакты вазелиновым маслом.
Для 24 В соедините две или четыре 12-вольтовые батареи последовательно.

Air Cleaner Element Replacement maintenance

⚠ Filters should be handled with care to prevent damage. If the filter does become damaged, install recommended replacement part.

Remove the air cleaner cover.
Remove thumb screw and gasket washer, then remove the element from air cleaner.
Wipe out the interior of the air cleaner housing and cover with a clean, damp cloth.
Install new element and secure with gasket washer and thumb screw.
Put on the air cleaner cover and secure.

Engine Oil Change maintenance

⚠ Crankcase pressure can blow out hot oil and cause serious burns. Do NOT check oil while the generator set is operating.

Tools: Oil drain pan

Bring the engine up to operating temperature and then shut if off.
Open the drain valve and collect the engine oil in a pan. When the crankcase is drained close the drain valve.
Fill the crankcase to the full mark on the dipstick. Allow for oil filters when drained or if changed.
Start the engine and check for oil leaks.
Shut off the engine and wait 15 minutes before checking the oil level. Add oil if required.

Filling the Cooling System (Standard Radiator and Heat Exchanger Sets) maintenance

⚠ Contact with hot coolant can result in serious burns. Do not bleed hot, pressurized coolant from a closed cooling system.

Remove the cooling system pressure cap and fill the system with water or a water/antifreeze mixture.
When the engine is first started, remove the pressure cap and monitor the coolant level.
As trapped air is expelled from the system, the coolant level will drop and additional coolant should be added.
Replace the pressure cap when the coolant level is stable.

Flushing and Cleaning the Cooling System maintenance

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

Tools: Flushing gun nozzle

Chemical Cleaning: use a good cooling system cleaner such as sodium bisulphate or oxalic acid and follow the supplier instructions. Neutralize and flush with clean water.
Flushing: open the upper and lower radiator hose connections and install the radiator cap.
Attach a flushing gun nozzle to the lower radiator hose connection and let the water run until the radiator is full.
Gradually apply air pressure to avoid damaging the core. Shut off the air and allow the radiator to refill. Repeat until water coming from the radiator is clean.
To flush the engine block, first remove the thermostat. Attach the flushing gun to the upper radiator hose and fill the block with water.
Restrict the lower radiator hose opening until the block is filled. Apply air pressure and force water from the lower opening. Repeat until water is clean.
Replace the thermostat and all hoses and refill cooling system.

Oil Filter Change maintenance

Tools: Filter wrench

Clean around the filter head.
Using a filter wrench, remove the oil filter.
Fill the filter with clean oil as recommended in Table 5-2.
Apply a light film of lubricating oil to the gasket sealing surface before installing the filter.
Install the filter until hand tight then turn an additional 1/2 turn.
Start engine to verify that filter is tight and does not leak.

Методика подготовки хладагента maintenance

⚠ Перед снятием крышки радиатора дайте системе остыть и стравите давление.

Добавьте требуемое количество воды в смесительный резервуар и растворите в ней требуемое количество DCA.
Добавьте требуемое количество антифриза и тщательно перемешайте.
Залейте хладагент в систему охлаждения и надежно заверните крышку радиатора.

Circuit breaker catalog number lookup operation

⚠ If the first 3 letters are PJP, start the search with PJ only.

⚠ If the catalog number starts with N, skip the N and begin the search with the second letter.

Locate the circuit breaker feature code or part number.
Use the charts to find the corresponding manufacturer circuit breaker catalog number.
Use the first letter of the catalog number to determine the breaker frame (if first letter is N, use the second letter).
Follow the corresponding website link to find the breaker catalog number description.
Search the catalog using the first 3 letters and first 5 numbers of the breaker catalog number.

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
120/208 thru 139/240	three phase	Broad range	12	150 deg C rise rating 230 kW / 288 kVA per ADS-212
120/240	single phase	Double delta	4	125 deg C rise rating 175/219 kW/kVA; 105 deg C rise rating 157/196 kW/kVA
240/416 thru 277/480	three phase	Broad range	12	150 deg C rise rating 255 kW / 319 kVA
347/600	three phase	Upper broad range (LBR)	6	150 deg C rise rating 230 kW / 288 kVA; lower broad range 110/190 thru 120/208, 220/380 thru 240/416

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 4B3.9 family

Part #	Description	Category
140-2641	Tube, Air Cleaner	Air filter
140-3218	Cleaner Assembly, Air (Includes	Air filter
982-0200	Air Filter	Air filter
300-3606	Voltage Regulator Installation (PMG-Excited Generators), Rev. P	Avr
300-3607	Voltage Regulator Installation (Self-Excited Generators), Rev. G	Avr
191-1965	Tensioner, Belt	Belt
191-2149-02	Tensioner, Belt	Belt
505-0055	Element, Fuel	Fuel filter
140-3255	*Hose, Breather	Hose
502-0827	Fitting, Hose – Barbed (1/2” ID Pipe to 3/4” ID Hose)	Hose
502-1317	Fitting, Hose Barbed	Hose
503-1707	*Hose, Intake (2–1/2” ID)	Hose
102-1490-00	Kit, Oil Sampler (Includes	Oil filter
102-1490-01	Valve, Oil Sampler	Oil filter
154-3078	Manifold, Oil Pressure	Oil filter
501-0575	Hose Assembly, Oil (3/4–16	Oil filter
501-0685	Line, Oil	Oil filter
504-0176	Valve, Oil Drain	Oil filter
140-1260	Fitting, Safety Filter	Service part / kit
201-3434-01	Diode, Positive (Forward) Includes Lead	Service part / kit
201-3434-02	Diode, Negative (Reverse) Includes Lead	Service part / kit
220-4289-31	Main stator assembly (broad range generators)	Service part / kit
220-4289-32	Main stator assembly (broad range generators)	Service part / kit
220-4289-33	Main stator assembly (broad range generators)	Service part / kit
220-4289-34	Main stator assembly (broad range generators)	Service part / kit
220-4289-35	Main stator assembly (broad range generators)	Service part / kit
220-4298-31	Main stator assembly	Service part / kit
220-4298-32	Main stator assembly	Service part / kit
220-4298-33	Main stator assembly	Service part / kit
220-4298-34	Main stator assembly	Service part / kit
220-4298-35	Main stator assembly	Service part / kit
220-4298-36	Main stator assembly	Service part / kit
300-4111	Auxiliary Relay Board (ARB), Rev. E	Service part / kit
319-0969	QS-Series Power Distribution Panel Wiring, Rev. G	Service part / kit
3905125	Solenoid, Fuel Shutoff – MCGGA, 24 Volt, Negative Ground Electrical System (Cummins part number)	Service part / kit
3921930	Solenoid, Fuel Shutoff – 12 Volt (Cummins part number)	Service part / kit
3921976	Solenoid, Fuel Shutoff – 24 Volt (Cummins part number)	Service part / kit
502-0153	Plug, Hex Head	Service part / kit
612-6487	7-Light DC Control Wiring Diagram, Sh 1 and 2 of 2, Rev. V	Service part / kit
612-6488	12-Light DC Control Wiring Diagram, Sh 1 and 2 of 2, Rev. W	Service part / kit
612-6489	AC Control Wiring Diagram (Without Meters), Rev. S, modified 6/2001	Service part / kit
612-6490	AC Control Wiring Diagram (With Meters), Rev. ZB, modified 1/2002	Service part / kit
625-2164	Generator Reconnection Diagrams, Sh 1 and 2 of 2, Rev. K	Service part / kit
625-2256	QS-Series Generator Connections When The Voltage Selector Switch Is Provided, Rev. B	Service part / kit
965-0520	Cooling Fan	Service part / kit
625-2141	Day Tank Pump Control Wiring, Rev. P	Pump
509-0266-01	Ring, O	Seal
150-2201	Sensor, Speed – Magnetic	Sensor
517-0291	Plug, Taper	Spark 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

What is the oil capacity of the Cummins/Onan 4B3.9-G?

The Cummins/Onan 4B3.9-G engine has an oil capacity of 11.5 liters.

What is the displacement of the Cummins/Onan 4B3.9-G?

The Cummins/Onan 4B3.9-G has a displacement of 3.92 liters.

Which generators use the Cummins/Onan 4B3.9-G engine?

The Cummins/Onan 4B3.9-G powers 7 generator set(s), including Cummins/Onan 28DGBB, Cummins/Onan 30DGHC, Cummins/Onan 35 DGBB, Cummins/Onan 36 DGBC, Cummins/Onan 40 DGBC.

What is a common problem with the Cummins/Onan 4B3.9-G engine?

A commonly reported issue on generators using the Cummins/Onan 4B3.9-G is: 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. Cause: The standard undesignated fault functions are programmed to shut down the set when a fault is sensed. Fault 1 is time 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.