Service parts for the DFM 300
Grouped by system, with how many of each the parts manual calls for.
Fuel system
1 requiredPrices captured from merchant listings; some links are affiliate links. Confirm against your serial number before ordering.
Specifications
| Fuel | Diesel |
|---|---|
| Frequency | 60.0 Hz |
| Standby power | 300 kW |
| Standby kVA | 375 |
| Oil capacity | 31.0 L |
| Alternator | 3 Phase 60 Hz YB |
| Phase | 3 |
| Power factor | 0.8 |
| Battery group | 8D |
| Battery voltage | 12 V |
| Battery quantity | 2 |
| Coolant capacity | 72 L |
| Dry weight | 3019 kg |
Engine
| Oil capacity | 40.0 L |
|---|---|
| Coolant capacity | 64.4 L |
| Displacement | 14.0 L |
| Aspiration | Turbo Aftercooled |
| Rated speed | 1800 rpm |
Maintenance & consumables
for the Cummins/Onan NTA855-G2| Item | Spec | Capacity | Part # | Interval | |
|---|---|---|---|---|---|
| Air filter | — | ||||
| Fuel filter | M-1398-1 | 500 hr | Amazon eBay | ||
| Oil filter | — | 250 hr | |||
| Battery | 127 A/hr | — | 500 hr | ||
| Belt | — | 100 hr | |||
| Coolant | 84.8 Litres | — | |||
| Coolant filter | — | 250 hr | |||
| Oil | 38.6 Litres | 38.6 Litres | — | 500 hr | |
| Spark plug | — | 250 hr |
Common questions
How many kW is the Cummins/Onan DFM 300?
The Cummins/Onan DFM 300 is rated 300 kW standby (375.0 kVA).
Which engine powers the Cummins/Onan DFM 300?
The Cummins/Onan DFM 300 is powered by the Cummins/Onan NTA855-G2 engine.
What kind of fuel does the Cummins/Onan DFM 300 run on?
The Cummins/Onan DFM 300 runs on Diesel.
What is the oil capacity of the Cummins/Onan DFM 300?
The Cummins/Onan NTA855-G2 engine in the Cummins/Onan DFM 300 has an oil capacity of 40.0 liters.
What alternator comes on the Cummins/Onan DFM 300?
The Cummins/Onan DFM 300 uses a 3 Phase 60 Hz YB alternator.
Which fuel filter part number does the Cummins/Onan DFM 300 take?
The Cummins/Onan DFM 300 uses fuel filter part number M-1398-1.
Troubleshooting
6Fault codes
| Code | Meaning | Remedy |
|---|---|---|
| PRE HI ENGINE TEMP | *2. PRE HI ENGINE TEMP lamp lights. Engine continues to operate. | 2. Indicates engine has begun to overheat and engine temperature has risen to approximately 205°F (97°C). If generator is powering non-critical and critical loads and cannot be shutdown, use the following: a. Reduce load if possible by turning off non-critical loads. b. Check air inlets and outlets and remove any obstructions to airflow. c. Open doors or windows in generator area to increase ventilation. If engine can be stopped, follow procedure in step 3. |
| HI ENG TEMP | *3. HI ENG TEMP lamp lights. Engine shuts down. | 3. Indicates engine has overheated (engine temperature has risen above 215°F/102°C) or coolant level is low (sets with coolant level sensor). Allow engine to cool down completely before proceeding with the following checks: a. Check coolant level and replenish if low. Look for possible coolant leakage points and repair if necessary. b. Check for obstructions to cooling airflow and correct as necessary. c. Check for a slipping fan belt and tighten if loose. d. Reset control and restart after locating and correcting problem. Contact an Onan Dealer or Distributor if none of the above. |
| PRE LO OIL PRES | *4. PRE LO OIL PRES lamp lights. Engine continues to operate. | 4. Indicates engine oil pressure has dropped to 20 psi (138 kPa). 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. |
| LO OIL PRES | *5. LO OIL PRES lamp lights. Engine shuts down NOTE: See also step 6. | 5. Indicates engine oil pressure has dropped to 14 psi (97 kPa). 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). |
| OVERCRANK | *6. OVERCRANK lamp lights and engine stops cranking. |
Symptoms & remedies
| Symptom | Remedy |
|---|---|
| *1. Green RUN lamp lights following engine start-up. | 1. Indicates all engine systems are normal. No corrective action required. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing. Full Cummins/Onan DFM 300 troubleshooting guide (24 entries) →
Parts
11| Part # | Description | Qty | System | |
|---|---|---|---|---|
| B-342-10 | CRANKCASE BREATHER | Breather | Amazon eBay | |
| CS-1075-1 | COOLANT FILTERS | Coolant filter | Amazon eBay | |
| CS-1130-1 | EXPANSION TANK CAP | Expansion tank cap | Amazon eBay | |
| ES-1779-1 | VOLTAGE REGULATOR AND EXCITATION SWITCH | Excitation switch | Amazon eBay | |
| M-1298 | CHECK OIL LEVEL (ON RIGHT SIDE OF ENGINE) | Oil filter | Amazon eBay | |
| M-1398 | STANDARD AIR CLEANER | 1 | Air filter | Amazon eBay |
| M-1398-1 | DUCT | Air inlet | Amazon eBay | |
| M-1398-2 | HEAVY DUTY AIR CLEANER (OPTIONAL) | 1 | Air filter | Amazon eBay |
| M-1739 | CYLINDER BLOCK RADIATOR DRAINCOCK AND OIL COOLER AND LOWER RADIATOR HOSE M-1739 | 1 | Hose | Amazon eBay |
| M-1740 | SUPPLY LINE, FILTER TO INJECTION PUMP FS-1424 | 1 | Fuel pump | Amazon eBay |
| S-1610 | VOLTAGE SELECTOR LIGHTS | Service part / kit | Amazon eBay |
Service, wear & replacement parts referenced for this model and its engine — confirm the exact part for your serial number. See the full parts catalog to search and cross-reference.