Troubleshooting your Marine Diesel

The rule of thumb when fault-finding your diesel is to only adjust one thing at a time. Stop and think how the engine operates and figure out the probable cause of any irregular operation, locating the trouble by elimination. Remember that the cause usually is a simple one rather than a mysterious and complicated one. The following checklist will be helpful in locating many ordinary engine problems.

The starter motor turns the engine too slowly

1. Battery capacity low. If your starter motor is emitting a characteristic hum then perhaps your starter battery is low on voltage. Check the level of charge in your starter battery with a voltmeter.
2. Bad electrical connections. The battery may have sufficient charge but a bad or intermittent connection from the battery to the starter circuit could be your problem.
3. Fault in starter motor. If you can try, check if it is possible to turn the starter motor by hand? Perhaps there is a physical object jammed somewhere in the belt or motor. Make sure that the power is off before putting hands anywhere that could cause injury. If you have them, release the decompression levers and try to move the belt by hand. Visually inspect as much of the starter motor as you can and note any damage to wires. Note that brushes are a common source of failure of small 12 volt motors.
4. Wrong grade of lubricating oil. Oil that is too viscous can cause resistance to movement in the engine crankcase, resulting in too much load on the starter motor. [Read more about oil grades]

The engine does not start

1. Starter motor turns engine too slowly. [Read relevant section above]
2. Fuel tank empty. Check the entire fuel system from the tank down to the primary filter.
3. Fault in stop control.
4. Restriction in a fuel pipe.
5. Fault in fuel lift pump.
6. Dirty fuel filter element.
7. Air in fuel system.
8. Fault in atomisers or atomisers of an incorrect type.
9. Cold start system used incorrectly.
10. Fault in cold start system.
11. Wrong type or grade of fuel used.
12. Fault in fuel injection pump.
13. Broken drive on fuel injection pump.
14. Timing of fuel injection pump is incorrect,
15. Valve timing is incorrect,
16. Bad compression.
17. Valves are not free.
18. Worn cylinder bores.
19. Leakage between valves and seats.
20. Piston rings are not free or they are worn or broken.

The engine is difficult to start

1. Starter motor turns engine too slowly. [Read relevant section above]
2. Fault in stop control.
3. Restriction in fuel pipe.
4. Fault in fuel lift pump.
5. Dirty fuel filter element.
6. Restriction in fuel cleaner or air induction system.
7. Air in fuel system.
8. Fault in atomisers or atomisers of an incorrect type.
9. Cold start system used incorrectly.
10. Fault in cold start system.
11. Restriction in fuel tank vent.
12. Wrong type or grade of fuel used.
13. Restricted movement of engine speed control.
14. Restriction in exhaust pipe.
15. Worn cylinder bores.
16. Leakage between valves and seats.
17. Piston rings are not free or they are worn or broken.

Not enough power

Excluding issues relating to incorrect propeller size, damaged or fouled propellers. The following checklist assumes that engine power has reduced from previously acceptable levels.

1. Restriction in fuel pipe.
2. Fault in fuel lift pump.
3. Dirty fuel filter element
4. Restriction in fuel cleaner or air induction system.
5. Air in fuel system.
6. Fault in atomisers or atomisers of an incorrect type.
7. Restriction in fuel tank vent.
8. Wrong type or grade of fuel used.
9. Restricted movement of engine speed control.
10. Restriction in exhaust pipe.
11. Engine temperature is too high.
12. Engine temperature is too low.
13. Fault in injection pump.
14. Timing of fuel injection pump is incorrect.
15. Valve timing is incorrect.
16. Bad compression.
17. Cylinder head gasket leaks.
18. Valves are not free.
19. Wrong high-pressure pipes.
20. Leakage between valves and seats.

Misfire

1. Restriction in a fuel pipe.
2. Fault in fuel lift pump.
3. Dirty fuel filter element.
4. Air in fuel system.
5. Fault in atomisers or atomisers of an incorrect type.
6. Fault in cold start system.
7. Engine temperature is too high.
8. Valve tip clearances are incorrect.
9. Fault in fuel injection pump.
10. Timing of fuel injection pump is incorrect.
11. Valve timing is incorrect.
12. Bad compression.
13. Cylinder head gasket leaks.
14. Valves are not free.
15. Wrong high-pressure pipes.
16. Leakage between valves and seats.

High fuel consumption

1. Restriction in filter/cleaner or air induction system.
2. Fault in atomisers or atomisers of an incorrect type.
3. Fault in cold start system.
4. Wrong type or grade of fuel used.
5. Restricted movement of engine speed control.
6. Restriction in exhaust pipe.
7. Engine temperature is too low.
8. Valve tip clearances are incorrect.
9. Fault in fuel injection pump.
10. Timing of fuel injection pump is incorrect.
11. Valve timing is incorrect.
12. Bad compression.
13. Cylinder head gasket leaks.
14. Valves are not free.
15. Worn cylinder bores.
16. Leakage between valves and seats.
17. Piston rings are not free or they are worn or broken.
18. Induction system leaks (turbocharged engines only).

Black exhaust smoke

1. Restriction in filter/cleaner or air induction system.
2. Fault in atomisers or atomisers of an incorrect type.
3. Fault in cold start system.
4. Wrong type or grade of fuel used.
5. Restriction in exhaust pipe.
6. Engine temperature is too low.
7. Valve tip clearances are incorrect.
8. Fault in fuel injection pump.
9. Timing of fuel injection pump is incorrect.
10. Valve timing is incorrect.
11. Bad compression.
12. Cylinder head gasket leaks.
13. Valves are not free.
14. Worn cylinder bores.
15. Leakage between valves and seats.
16. Piston rings are not free or they are worn or broken.
17. Turbo-charger impeller is damaged or dirty (turbocharged engines only).
18. Induction system leaks (turbocharged engines only).

— Read our more in-depth article on engine smoke here —

Blue or white exhaust smoke

1. Wrong grade of lubricating oil. [Read more about oil grades]
2. Fault in cold start system.
3. Engine temperature is too low.
4. Too much oil or oil of wrong specification used in wet type air cleaner (if fitted). [Read more about wet-type air filters]
5. Timing of fuel injection pump is incorrect.
6. Valve timing is incorrect.
7. Bad compression.
8. Cylinder head gasket leaks.
9. Worn cylinder bores.
10. Piston rings are not free or they are worn or broken.
11. Valve stems and/or guides are worn.
12. Piston is damaged.
13. Valve stem seal (if fitted) is damaged.
14. Lubricating oil seal of turbo-charger is leaking (turbocharged engines only).

— Read our more in-depth article on engine smoke here —

The pressure of the lubricating oil is too low

1. Wrong grade of lubricating oil. [Read more about oil grades]
2. Not enough lubricating oil in sump.
3. Defective gauge or sensor.
4. Dirty lubricating oil filter element.
5. Crankshaft bearings are worn or damaged.
6. Lubricating oil pump is worn.
7. Relief valve does not close.
8. Relief valve spring is broken.
9. Fault in suction pipe of lubricating oil pump.
10. Restriction in sump strainer.

The engine is over-heating

1. Insufficient coolant level.
2. Defective thermostat.
3. Leakage of exhaust gases into cooling system.
4. Leakage of coolant into the cylinders due to faulty cylinder head gasket.
5. Defective coolant pump.
6. Clogged coolant jacket / channels in engine head.
7. Incorrect injection timing.
8. Reduced injection pressure.
9. Wrong type or grade of fuel used.
10. Fault in atomisers or atomisers of an incorrect type. Poor nozzle spray.
11. Defective or deteriorated engine oil.
12. Fault in oil pump.
13. Insufficient engine oil level.

Engine knocking

1. Fault in fuel lift pump.
2. Fault in atomisers or atomisers of an incorrect type.
3. Fault in cold start system.
4. Wrong type or grade of fuel used.
5. Engine temperature is too high.
6. Valve tip clearances are incorrect.
7. Too much oil or oil of wrong specification used in wet type air cleaner (if fitted). [Read more about wet-type air filters]
8. Timing of fuel injection pump is incorrect.
9. Valve timing is incorrect.
10. Valves are not free.
11. Worn cylinder bores.
12. Piston rings are not free or they are worn or broken.
13. Crankshaft bearings are worn or damaged.
14. Piston is damaged.
15. Piston height is incorrect.
16. Valve spring is broken.

Erratic running

1. Fault in stop control.
2. Restriction in fuel pipe.
3. Fault in fuel lift pump.
4. Dirty fuel filter element.
5. Restriction in fuel cleaner or air induction system.
6. Air in fuel system.
7. Fault in atomisers or atomisers of an incorrect type.
8. Fault in cold start system.
9. Restriction in fuel tank vent.
10. Restricted movement of engine speed control.
11. Engine temperature is too high.
12. Valve tip clearances are incorrect.
13. Too much oil or oil of wrong specification used in wet type air cleaner (if fitted). [Read more about wet-type air filters]
14. Fault in fuel injection pump.
15. Bad compression.
16. Valves are not free.
17. Wrong high-pressure pipes.
18. Piston rings are not free or they are worn or broken.
19. Piston is damaged.
20. Valve spring is broken.

Vibration

1. Fault in atomisers or atomisers of an incorrect type.
2. Restricted movement of engine speed control.
3. Engine temperature is too high.
4. Fan damaged.
5. Fault in engine mountings or flywheel housing.
6. Fault in injection pump.
7. Bad compression.
8. Cylinder head gasket leaks.
9. Valves are not free.
10. Wrong high-pressure pipes.
11. Piston rings are not free or they are worn or broken.
12. Piston is damaged.
13. Flywheel housing or flywheel is not aligned properly.

The pressure of the lubricating oil is too high

1. Wrong grade of lubricating oil. [Read more]
2. Defective sensor or gauge.
3. Relief valve not opening.

Crankcase pressure

1. Restriction in the breather pipe.
2. Vacuum pipe leaks or fault in exhauster.
3. Cylinder head gasket leaks.
4. Worn cylinder bores.
5. Piston rings are not free or they are worn or broken.
6. Valve stems and/or guides are worn.
7. Piston is damaged.

Poor compression

1. Restriction in fuel cleaner or air induction system.
2. Valve tip clearances are incorrect.
3. Valve timing is incorrect.
4. Cylinder head gasket leaks.
5. Valves are not free.
6. Worn bores.
7. Leakage between valves and seats.
8. Piston rings are not free or they are worn or broken.
9. Valve stems and/or guides are worn.
10. Piston height is incorrect.
11. Valve spring is broken.

Engine stops and starts

1. Dirty fuel filter element.
2. Restriction in fuel filter or air induction system.
3. Air in fuel system.