Marine engines can experience a number of faults, and we should know them all.
It is good to understand when you can intervene and when you should contact authorized workshops.
Remember it’s not just a matter of skill!
In my experience as a marine surveyor in Italy, I have learned that it’s often better not to get involved in some repairs for warranty reasons.
Let’s look at the most common malfunctions.
They are in order of frequency.
Most common marine engine failures
1) The engine won’t start or the panel won’t turn on
The first thing to do is to try putting in neutral and restarting because the inverter may have the gear engaged.
The second problem could be the engine seized. Or the starter motor could be stuck or defective, and in that case you’d better check that the pinion of the motor fits into the flywheel.
Another possibility is that the battery is dead or the cable terminals on the battery are not tightly closed or oxidized. Finally, the starter switch could be defective. In any case, outboard motors can be started in an emergency by lanyard.
Remember that lanyard may be
1) Already mounted on the grille;
2) To be mounted.
In small inboard engines there may be a crank instead.
2) The engine runs but does not start
There could be lack of fuel or no inflow, or water in the fuel and so the fuel filters should be cleaned. Finally, there could be an emergency stop engaged, so the appropriate switch should be checked.
There are also some differences between gasoline engine and diesel engine. In the gasoline engine, you can try pulling the air knob before retrying starting.
Or in the case of a flooded carburetor, one can shut off the fuel and wait a few minutes, perhaps removing the spark plugs and airing the combustion chambers and then remounting the cleaned and dried spark plugs. Or the ignition circuit may be having problems. If even by fixing and readjusting its various parts there is no change, it is advisable to call for service.
On the other hand in the case of the Diesel engine, if there is air in the injection circuit, it can be purged by filling the circuit with the appropriate pump by opening the purge valves to remove all the air, or de-air the injectors by manually operating the injection pump. There could be failed glow plugs, stuck injector, faulty injection pump, or stuck valves. For the latter four reasons, it is time to seek service.
3) The engine stops just after starting
In this case the fuel valve or tank vent may be closed. Then it is worth checking the oil level. In the case of the gasoline engine, the carburetor might be dirty, in which case it is worth asking for service.
For the diesel engine, on the other hand, there might be air in the injection pump and you need to bleed the circuit as explained above. Or, there could be water in the fuel and it is worthwhile at this point to clean the tank and install the separator filter.
The injection pump could also be defective, and here it is worth asking for service. We also have the possible dirty fuel filter or clogged air filter or idle to adjust.
4) Engine stops
The first action to take is to check that there is enough fuel. The fuel supply could also be cut off or finally there could be air in the injection circuit in the case of the Diesel engine.
There could also be a problem with the cooling circuit so it is best to check the water circulation and wait for the engine to cool down.
There could be a fault in the lubrication circuit, in which case the oil sight glass should be checked. Check for water or impurities in the fuel, and check that the propeller shaft is not stuck with the inverter engaged or that there is no fault in the electrical circuit (in the case of internal combustion engines).
5) The motor is overheating
There may be the impeller to be replaced in the circulating pump. Or the refrigeration circuit might be dirty, and it needs to be cleaned when the engine is stopped.
Finally, there could be a closed or clogged sea inlet, at which point the engine must be stopped immediately: open the sea inlet valve and proceed to clean the filter. All this applies to the inboard engine, while for an outboard engine it is worth checking the stern exhaust water jet to make sure the cooling pump is working.
Or, the impeller may need to be replaced.
6) The engine tends to drop in rpm
Check that the propeller shaft is not blocked and that the fuel filters are clean.
In the case of the gasoline engine, there may be water in the carburetor that needs to be purged or dirt – and in the latter case it is better to ask for service. Or, there might be no idle adjustment: fix it with the appropriate screw.
Finally, it is easy for the spark plugs to be old or dirty or in the case of the Diesel engine there is fuel, dirt or air algae in the circuit.
7) The engine emits white or blue smoke from the exhaust
In this case for a 4-stroke engine the piston rings may be worn and in that case you need to ask for service. Also check the oil in the crankcase: it may need to be decreased.
In the two-stroke engine, on the other hand, the mixture is often too rich in oil, so it is a case of adding gasoline to the tank.
8) Black smoke from the exhaust
In these cases, the engine often hits the head and does so because the fuel is old or dirty or the carburetor dirty or damaged (in the case of the gasoline engine). Conversely, in the case of the Diesel engine, the air filter or fuel filter could be dirty.
Also check the injectors: they could be starred and here, too, you need to ask for service.