Sure, electric motors are great, incredibly reliable, and require almost no maintenance. But they haven’t completely replaced internal combustion engines yet, so every now and then, old-school boat owners have to roll up their sleeves and get their hands dirty to figure out why their ICE suddenly broke down.
Generally speaking, if a gasoline engine initially fails to start, there can only be two possible causes: either the fuel system or the ignition system (or both at once) is faulty. In a diesel engine, the number of causes is reduced to just the fuel system. At least in the warm season.
But that was in the past. Today, we must add electronics that control these processes to the main causes.
However, when your inboard or outboard ICE suddenly stalls, starts making strange noises, or loses power, here are the components that you should look at first in search of the cause:
1. Electrics
This includes both the ignition system and the wiring. There are no spark plugs in a diesel engine, since it uses a compression ignition system. Therefore, the following steps are relevant only for gasoline engines.
First, you need to make sure that the ignition system of the fuel mixture is in good working order. To do this, simply unscrew the spark plugs and check for a stable spark.
At the same time, make sure that the spark plugs have clean, carbon-free electrodes and the required gap between them, and they are tightened with the required force to prevent loss of compression in the cylinders.
In addition, check whether the marking of the spark plugs matches that indicated in the engine manual. The models of the spark plugs must be exactly the same, no deviations are allowed.
Older outboard motors may have mechanical ignition timing adjustments, which require precise adjustment of the ignition time of the fuel mixture.
If there is no spark, then check all the contacts, terminals, fuses, battery, electronic units, etc. Electrics, due to which a failure in the operation of an outboard motor or a stationary gasoline engine may occur, can have various variations and protection systems, but in general, if there is a spark, then we move on to the next possible cause.
2. Fuel system
The second most common cause of failure of boat motors. Or the first, depending on where you refuel.
Marine engines have different fuel supply systems, depending on the design and type, but fuel filters and injectors can become clogged in all of them. Also, water can get into gasoline or diesel, air leaks can form in the fuel line and places where the mixture is supplied, or the fuel pump can break down.
Among the most common cases, it is necessary to note the most banal one – lack of fuel.
3. Engine overheating
All modern motors are protected from overheating, have warning systems and emergency shutdown. However, older models can be vulnerable to such problems. As well as simple low-power outboards.
In most cases, boat engines, both stationary and outboard, have a cooling system with sea water. This can be either direct cooling or combined, with a closed circuit.
Sea water is supplied by a water pump. In this pump, the most critical and only moving element is the impeller, which is most often made of soft materials. It is the one that regularly fails.
In outboard motors, the pump is built directly into the deadwood above the gearbox.
Another problem is debris and algae, which can clog the water intake. If water stops flowing into the pump, then in addition to the risk of overheating the engine, the impeller begins to rotate dry and eventually melts from friction. Therefore, even after cleaning the water intake, the cooling system may not work.
Also (rarely) a faulty or old thermostat valve gets stuck in the closed position. And in some cases, the cooling channels, including the cylinder block jacket, can have abundant salt or mud build-up, preventing normal water circulation.
4. Propeller
The propeller can break when hitting an underwater obstacle or when running aground. But most often, it simply collects various debris underwater.
Fishing nets, line and ropes are perfectly wound on the propeller. The consequences depend on the design of the drive. Sometimes an almost invisible thin fishing line wound on the propeller shaft can completely ruin the seals.
Typically, propeller problems manifest as loss of thrust, changes in engine performance, and unusual noises.
5. Gearboxes
The drive design can use a variety of schemes, from the simplest direct transmission to transom sterndrives. Any gearbox is a weak link, but most often, of course, problems arise with external ones.
Hitting underwater obstacles, water getting through seals and gaskets, irregular maintenance with oil changes – all this is fraught with expensive repairs.
Gearbox problems often present the same symptoms as propeller problems, from loss of thrust to unusual noises.
6. Drive belts
Yes, they wear out, stretch and even break. Therefore, it is always a great idea to have a spare set of belts on board.
7. Malfunctions of the valve timing and crank mechanisms
In an internal combustion engine, consisting of hundreds of important parts under constant load, anything can fail at any time. Piston rings, camshafts, valves and even cylinder heads.
But this point is in last place for a reason, because with time-tested, reliable marine engines, such major breakdowns happen quite rarely. Yes, outboards are less durable, but even for them, piston group failure is unlikely.
Of course, all this is provided that you do not operate the engine at the limit of its capabilities, do not pour all sorts of crap into the gas tank and crankcase in order to save money, and at least once a year carry out maintenance.