The Cummins/Onan QSK38 is a 37.8 L 12-cylinder 4-cycle industrial diesel engine rated at 1800 rpm. It powers generator sets from Cummins/Onan, including the C1250D6E and C1500D6E. It holds 186 L (49.1 gal) of oil and 112 L (29.6 gal) of coolant.
Also known as: Cummins QSK38
Part of the Cummins/Onan QSK38 engine family — 7 variants share parts & fitment.
| Oil capacity | 186.0 L |
|---|---|
| Coolant capacity | 112.0 L |
| Displacement | 37.8 L |
| Cylinders | 12 |
| Aspiration | 4-cycle industrial diesel |
| Rated speed | 1800 rpm |
How to read your Cummins/Onan engine serial & model number →
Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan QSK38.
| Item | Spec | Capacity | Part # | Interval | |
|---|---|---|---|---|---|
| Air filter | — | ||||
| Fuel filter | — | ||||
| Oil filter | — | ||||
| Battery | — | ||||
| Belt | — | ||||
| Coolant | — | ||||
| Oil | — | ||||
| Spark plug | — |
Pooled from every document that names this exact engine — confirm the interval and part number against your unit's serial number.
| Item | Action | Hours | Months | Notes |
|---|---|---|---|---|
| Lubricating oil | Test | 250 hr | 6 mo | First service — For high horsepower engines with Eliminator™ oil filter option: take oil samples every 250 hours and analyze per Cummins Engine Oil Recommendations Bulletin 3810340; repeat for at least three oil change intervals. |
| filters | Change | 1000 hr | with CENTINEL, depending on load factors | |
| ELIMINATOR self cleaning filter core | Other | 1500 hr | Requires servicing only every 1,500 hours. Saves up to 90% of lube system maintenance costs and increases productivity. | |
| fuel filter | Change | 1500 hr | Fleetguard NanoNet media | |
| engine oil | Change | 4500 hr | with CENTINEL, railway applications |
Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.
| Fluid | Grade | Standard | Ambient | Capacity | Notes |
|---|---|---|---|---|---|
| Engine oil | Cummins Engine Oil Recommendations Bulletin 3810340 | Used to analyze oil samples for high horsepower engines with Eliminator™ oil filter option. | |||
| Fuel | 40-50 Cetane number | ASTM D975 No. 2-D | 300-500 ppm Sulfur | ||
| Fuel | 40-50 Cetane number, ASTM D975 No. 2-D | ASTM D975 | 300-500 ppm Sulfur; #2 Diesel low-sulfur/ultra-low sulfur required for start-up | ||
| Fuel | B100 biodiesel | ASTM D6751 | Must conform prior to blending; revised to include a cold soak test; stability requirement still in effect. | ||
| Fuel | B20 biodiesel blend | ASTM D7467 | Applies to biodiesel blends B6–B20; includes oxidation stability requirement; replaces Cummins' previous EMA B20 specification requirement. Must be purchased from a BQ9000 Certified Marketer; B100 must be sourced from a BQ9000 Accredited Producer. | ||
| Fuel | B5 biodiesel | All Cummins automotive and industrial engines are compatible with B5 biodiesel. | |||
| Fuel | biodiesel (Europe) | EN 14214 | Published by CEN, European Committee for Standardization. Equivalent biodiesel specifications required internationally. |
Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.
| Code | Name | Meaning | Severity | Action |
|---|---|---|---|---|
| 27 | Low AC voltage shutdown | Voltage on any phase has dropped below a preset value. Adjustable over a range of 50-95% of reference voltage, time delay 2-20 seconds. Default value is 85% for 10 seconds. Function tracks reference voltage. Control does not nuisance trip when voltage varies due to the control directing voltage to drop, such as during a V/Hz roll-off or synchronizing. | Shutdown | Shutdown genset. |
| 32 | Reverse power shutdown | Adjustment range: 5-20% of standby kW rating, delay 1-15 seconds. Default: 10%, 3 seconds. | Shutdown | Shutdown genset. |
| 40 | Reverse Var shutdown | Shutdown level is adjustable: 15-50% of rated Var output, delay 10-60 seconds. Default: 20%, 10 seconds. | Shutdown | Shutdown genset. |
| 46 | Negative sequence overcurrent warning | Control protects the generator from damage due to excessive imbalances in the three phase load currents and/or power factors. | Warning | Warning. |
| 51 | Overcurrent warning/shutdown | Implementation of the thermal damage curve with instantaneous trip level calculated based on current transformer ratio and application power rating. | Shutdown | Shutdown or warning. |
| 51G | Ground fault overcurrent | Control detects a ground fault either by an external ground fault relay via a contact input or the control can measure the ground current from an external current transformer. Associated time delays and thresholds are adjustable via InPower or HMI. | Shutdown | Shutdown or warning. |
| 59 | High AC voltage shutdown | Output voltage on any phase exceeds preset values. Time to trip is inversely proportional to amount above threshold. Values adjustable from 105-125% of nominal voltage, with time delay adjustable from 0.1-10 seconds. Default value is 110% for 10 seconds. | Shutdown | Shutdown genset. |
| 81 u | Under frequency shutdown | Genset output frequency cannot be maintained. Settings are adjustable from 2-10 Hz below reference governor set point, for a 5-20 second time delay. Default: 6 Hz, 10 seconds. Under frequency protection is disabled when excitation is switched off, such as when engine is operating in idle speed mode. | Shutdown | Shutdown genset. |
| 81o | Over frequency shutdown/warning | Genset is operating at a potentially damaging frequency level. Settings are adjustable from 2-10 Hz above nominal governor set point for a 1-20 second time delay. Default: 6 Hz, 20 seconds, disabled. | Warning | Warning or shutdown. |
Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.
Tools: Wrench
⚠ B20 has a solvent nature and may clean the vehicle fuel tank and lines.
Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.
| Part # | Description | Category |
|---|---|---|
| MCBQSK0068 | Water Pump Gasket Set | Gasket |
| M-2885786 | Cylinder Liner Kit | Service part / kit |
| M-3007525 | Cylinder Liner Kit | Service part / kit |
| M-3022157 | Cylinder Liner | Service part / kit |
Parts cataloged across all variants of this engine family — verify the exact part fits your specific variant and serial number before ordering.
The Cummins/Onan QSK38 engine has an oil capacity of 186.0 liters.
The Cummins/Onan QSK38 has a displacement of 37.8 liters with 12 cylinders.
The Cummins/Onan QSK38 powers 3 generator set(s), including Cummins/Onan C1250D6E, Cummins/Onan C1500D6E, Cummins/Onan QSK38.
A commonly reported issue on generators using the Cummins/Onan QSK38 is: Derate. Fix: The Derate function reduces output power of the genset in response to a fault condition. If a Derate command occurs while operating on an isolated bus, the control will issue commands to reduce the load on the genset via contact closures or Modbus. If a Derate command occurs while in utility parallel mode, the control will actively reduce power by lowering the base load kW to the derated target kW..