Cummins/Onan 4BT 3.9-G4 Engine Engine
The Cummins/Onan 4BT 3.9-G4 is a 3.92 L 4-cylinder turbucomprimido engine rated at 1800 rpm, producing up to 73.9 kW. It powers generator sets from Cummins/Onan, including the C50 D6, C65D6, C70 and C70D5. It holds 10.9 L (2.9 gal) of oil and 15.5 L (4.1 gal) of coolant.
Also known as: Cummins 4BT 3.9-G4
Engine specifications
| Oil capacity | 10.9 L |
|---|
| Coolant capacity | 15.5 L |
|---|
| Displacement | 3.92 L |
|---|
| Cylinders | 4 |
|---|
| Aspiration | Turbucomprimido |
|---|
| Rated speed | 1800 rpm |
|---|
| Gross power | 73 kW |
|---|
Generator sets powered by this engine
5Common problems
15- Over Current 1471
- Low Coolant Level 197
- Weak Battery 1442
- Under Frequency 1448
- Too Long in Idle 2342
- 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.
Fix: 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.
Fix: Indicates Run/Stop/Remote switch is in the Stop position which will prevent automatic starting if an automatic transfer switch is used. Move the Run/Stop/Remote switch to the Remote position for automatic starting. - Status Indicators are not functioning properly.
Fix: Check the status indicators for any visible damage or loose connections. If the issue persists, refer to the Fault Code Table for further troubleshooting. - Speed/Hz Match 1469
- Speed Signal Lost 121
- Shutdown After Battle Short 1123
- Short Circuit 1445
- Same features as Fault 1 (Normally set for timed shutdown). FAULT 2
- Remote Emergency Stop 1434
- Pre-Low Oil Pressure Sensor 143
Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan 4BT 3.9-G4.
Maintenance schedule
| Item | Spec | Capacity | Part # | Interval | |
|---|
| Air filter | Maximum Air Cleaner Restriction, in. H2O (kPa) 25.0 (6.2) | | — | 500 hr | find |
| Fuel filter | Single spin-on canister, full flow | | — | 500 hr | find |
| Oil filter | Single spin-on canister, full flow | | — | 500 hr | find |
| Belt | V-belt | | — | 1000 hr | find |
| Coolant | Coolant capacity (only engine) | 7.2 l | — | | |
| Oil | 104oF (40oC) ambient radiator | 11.5 L | — | 1000 hr | |
Pooled from every document that names this exact engine — confirm the interval and part number against your unit's serial number.
Common questions
What is the oil capacity of the Cummins/Onan 4BT 3.9-G4?
The Cummins/Onan 4BT 3.9-G4 engine has an oil capacity of 10.9 liters.
What is the displacement of the Cummins/Onan 4BT 3.9-G4?
The Cummins/Onan 4BT 3.9-G4 has a displacement of 3.92 liters with 4 cylinders.
Which generators use the Cummins/Onan 4BT 3.9-G4 engine?
The Cummins/Onan 4BT 3.9-G4 powers 5 generator set(s), including Cummins/Onan C50 D6, Cummins/Onan C65D6, Cummins/Onan C70, Cummins/Onan C70D5, Cummins/Onan DGCB.
How often should you change the oil in the Cummins/Onan 4BT 3.9-G4?
The Cummins/Onan 4BT 3.9-G4 oil change interval is every 1000 hours.
What is a common problem with the Cummins/Onan 4BT 3.9-G4 engine?
A commonly reported issue on generators using the Cummins/Onan 4BT 3.9-G4 is: Over Current.