Service parts for the MDL3
Grouped by system, with how many of each the parts manual calls for.
Fuel system
1 requiredOil system
1 requiredBelts
1 requiredPrices captured from merchant listings; some links are affiliate links. Confirm against your serial number before ordering.
Specifications
| Fuel | No.2 Diesel |
|---|---|
| Frequency | 50.0 Hz |
| Prime power | 1 kW |
| Oil capacity | 4.7 L |
| Voltage options | 12 V, 24 V |
| Phase | {'value': 1, 'frequency_hz': 50},{'value': 3, 'frequency_hz': 60} |
| Power factor | [0.8] |
| Battery cranking | 500 CCA |
| Battery voltage | 12 V |
| Battery quantity | 2 |
| Coolant capacity | [9.4] L |
| Max ambient | [30, 40] °C |
| Fuel tank | 57.0 L |
Maintenance & consumables
for the Cummins/Onan Q 3A1.7| Item | Spec | Capacity | Part # | Interval | |
|---|---|---|---|---|---|
| Air filter | Check for oil, fuel, cooling and exhaust system leaks. Check exhaust system audibly and visually. | — | |||
| Fuel filter | Fuel Filter Element | 149-1758 | Amazon eBay | ||
| Oil filter | Oil Filter (ESN 5312 6274 and Below) | 122-0602 | Amazon eBay $20.69 | ||
| Battery | Check the terminals on the battery for clean and tight connections. Loose or corroded connections create resistance which can hinder or prevent starting. | — | |||
| Belt | Water Pump Belt | 511-0147-14 | Amazon eBay | ||
| Coolant filter | — | ||||
| Oil | — | ||||
| Spark plug | — |
Common questions
What engine is in the Cummins/Onan MDL3?
The Cummins/Onan MDL3 is powered by the Cummins/Onan Q 3A1.7 engine.
What kind of fuel does the Cummins/Onan MDL3 run on?
The Cummins/Onan MDL3 runs on No.2 Diesel.
What's the oil capacity on a Cummins/Onan MDL3?
The Cummins/Onan Q 3A1.7 engine in the Cummins/Onan MDL3 has an oil capacity of 4.6 liters.
Which oil filter part number does the Cummins/Onan MDL3 take?
The Cummins/Onan MDL3 uses oil filter part number 122-0602.
What fuel filter does the Cummins/Onan MDL3 use?
The Cummins/Onan MDL3 uses fuel filter part number 149-1758.
Troubleshooting
6Symptoms & remedies
| Symptom | Cause | Remedy |
|---|---|---|
| Engine does not crank. | Battery dead. | Check battery per Checkout [A] and recharge or replace. Check battery charger operation per jumper battery cable B+ connection to 81 starter solenoid terminal. Does engine crank? If no, check battery cables for clean tight connections and motor-if bad, repair or replace. (ref. Checkout [B]). Check B1 starter solenoid With S11 in Start position, is battery voltage present between K11 terminal S and ground? If not, check B+_/wiring between K11 and B1 solenoid terminal. Replace if bad. If K11 does not energize, test per Checkout [D] and replace if bad. Is battery voltage present at B1 solenoid terminal with S11 in Start position. Check breakers CB11, CB13, or fuse F1. Check S11 and replace if bad. Check B+/wiring to S11 start terminal and K11 -S terminal. |
| Engine cranks but does not start. | Heater circuit operating improperly or incorrect fuel. | Check heater solenoid K13 per Checkout [HI. Check diodes CR2 and CR3, wiring, heaters, and resistors START. Check fuel supply system: fuel tank level, shutoff valves, fuel lines and connections, fuel filters, transfer pump and injection blue-white, and fuel flow steady from fuel return line. Check fault reset breaker. Check B+ circuit through K11-I to Engine monitor board terminal All-1, All-CB12 Line, All-SW B+, to K1. Does K1 fuel solenoid energize when S l l is in Start position? Incorrect fuel? See Operator’s Manual recommendations. |
| Engine starts but stops after running several seconds. | A fault condition indicated by fault breaker CB12 on control panel or DC control breaker trips when the generator set is started. | Check for a possible fault condition. If none, check fault monitors S1 through S5 and fault breaker CB12 for improper wiring. Check all B+ wiring for shorts to ground. |
| NO AC OUTPUT VOLTAGE AT RATED ENGINE RPM | Check lead continuity between AC terminals on A1 and terminals 2 and 3 on VR21 per TEST [Ml. Replace defective field breaker. Remove one lead from breaker and check continuity with ohmmeter. Is breaker open? Is control panel field breaker CB21 on? | |
| Voltage is unstable, high or low | Push to reset breaker. Does generator AC output voltage build up? If no, flash exciter field per TEST [D]. Does generator output voltage build up? | |
| Residual voltage across terminals 2 and 3 of VR21 is less than 5 to 10 VAC | Disconnect stator leads from leads 1 and 2 from AC across the leads. Is residual voltage 4 and 5,5 VDC or more now? Check reactor CMR21 and transformer T21 per TESTS (B) and (E). For shorts per TEST [MI. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Repair guides
6- AC SCHEMATIC - ELECTRONIC REG
- ASSEMBLE DRIVE DISK
- ELECTRICAL SCHEMATIC
- TESTING ROTATING RECTIFIERS
- TESTING GENERATOR STATOR
- WIRING HARNESS CHECK
Step-by-step procedures compiled from the Cummins/Onan service manual for this model.
Parts
12| Part # | Description | Qty | System | |
|---|---|---|---|---|
| 122-0602 | Oil Filter (ESN 5312 6274 and Below) | Oil filter | Amazon eBay $20.69 | |
| 122-0764 | Oil Filter (ESN 5312 6275 and Up) | Oil filter | Amazon eBay | |
| 132-0276 | Sea Water Pump Impeller kit w/cover & gasket | Impeller | Amazon eBay | |
| 132-0317 | Sea Water Pump Impeller | Impeller | Amazon eBay | |
| 149-1758 | Fuel Filter Element | Fuel filter | Amazon eBay | |
| 333-0220 | Glow Plug (12 Volt) | Glow plug | Amazon eBay | |
| 511-0147-14 | Water Pump Belt | Belt | Amazon eBay | |
| FSl245 | Battery | 1 | Battery | Amazon eBay |
| FSl496 | Fuel Filter | 1 | Fuel filter | Amazon eBay |
| 934-0500 | 1 | Service part / kit | Amazon eBay $49.00 | |
| SG13753r | AC Control Breakers | Service part / kit | Amazon eBay | |
| sa377 | Resonator | 1 | 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.
Fuel consumption
| Rating | Load | L/h | gal/h |
|---|---|---|---|
| Prime | 50% | 11.36 | 3.0 |
| Prime | 100% | 23.09 | 6.1 |
Available documents
Parts manual — 934-0229 Onan MDL3 MDL4 MDL6 (spec A) Marine Genset Parts manual (01-2010) (Cummins/Onan)Parts manual — F-1229D Onan Marine Service Parts & Maintenance Schedule Card (09-2002) (Cummins/Onan)Service manual — 934-0124 Onan MDL3 MDL4 MDL6 Marine Genset Operator's manual (03-1992)Service manual — 934-0500 Onan MDL3 MDL4 MDL6 Marine Genset Service manual (08-1991) (Cummins/Onan)