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Engine overheats.
Supply clogged.
If the temperature alarm goes off, your engine will get too little or no cooling water. The first point is the supply from the shut-off valve, which can be closed or there is a blockage due to, for example, a plastic bag on the outside of the ship. Loosening the hose and blowing through can clear the blockage if it is on the outside or in the hose, a strainer can also be closed with dirt
Air in cooling system.
Air leak in the enclosure lid, hose clamps no longer close properly.
Engine internally dirty.
Dirty / slipped cooling channels in direct cooled engines are more common with age. Sometimes it can be solved by using a cleaning agent, but often a head disassembly is necessary to flush rust and dirt from the channels. Especially the transition from block to head sometimes clogs up.
Heat exchanger.
If the engine has a heat exchanger, it can clog up over time. You can clean the pipes of the heat exchanger with a pipe cleaner. Check the level when the engine is cold and, if necessary, top it up a few centimeters below the filler cap of the heat exchanger and with an expansion vessel to about half. Note: The system is under pressure when the engine is hot. Wear protective gloves and unscrew the cap in two steps. After less than a quarter turn, the cap remains locked and the pressure can escape along with the hot coolant. then turn further and the cap is loose.
Impeller pump.
With an impeller that is missing 1 or more blades, the motor temperature will increase. This also happens if the impeller pump cover is worn too much. A lid can often be turned in an emergency, provided the paint has been removed.
Thermostat defective.
A faulty thermostat ensures that the engine is no longer cooled and runs warm, modern thermostats open when they stop working. The thermostat housing bypass may be narrowed or the thermostat scaled. In an emergency, you can remove the faulty thermostat and sail back to port.
V-belt.
On many engines the impeller pump (outboard water) or the circulation pump (coolant pump) with a V-belt driven, whether or not in combination with a dynamo. If the V-belt drives a cooling pump, it is important that the V-belt is in good condition and has the correct tension.
Changing engine temperature.
The thermostat expands the cooling circuit as needed. If the cooling water becomes too hot, the thermostat valve will open and allow a larger amount of cooling water through. To prevent a cold wave of cooling water from being pumped through the engine block when opening, causing the valve to close again immediately, the thermostat has a bypass hole. Nevertheless, some engines suffer from a strongly fluctuating cooling water temperature. This problem can often be remedied by puncturing or enlarging the (calcified) bypass hole. Also check that the thermostat is mounted in the correct position. The hole should be at the top (at twelve o'clock).
Motor is overloaded.
Too big screw and / or pitch. Dirt in the propeller. Too much resistance in the exhaust system.
Lubrication.
In addition to lubrication, oil also has the task of cooling the engine. If too little oil is pumped around (oil pressure too low), the engine will also heat up. Clogged oil filter, worn oil pump, oil pressure valve, and / or dirty oil cooler can contribute to a warmer engine.
