CHAPTER 4


Drive chain troubleshooting Engine


All the trouble-shooting methods described below assume that catastrophic mechanical failure has not taken place. In most cases this is a reasonable assumption, since the marine diesel engine is extremely robust. If the engine stops in service it will almost certainly be because it has suffered some form of fuel problem or has overheated. The moment the temperature gauge or audible alarm indicates overheating, the engine should be shut down as soon as safely possible. Running in an overheated state may severely damage the unit or even cause it to seize up and stop altogether.


Overheating


Most marine engines are cooled by a liquid circulated by a pump, as are engines in motorcars. Unlike automotive applications, which use radiators to control the temperature of the coolant, the marine unit favours a heat exchanger which is itself cooled by sea water. This ‘raw water’ is drawn into the boat via a seacock, passed through a filter and then round the heat exchanger which is typically bolted to the engine. From there, the warm water is


Anti-siphon valve


Exhaust outlet


Sea water filter / Strainer Heat exchanger


expelled over the side, usually by way of the engine exhaust outlet where it cools and silences the gases. Most overheating problems arise from the seawater system. If seawater stops flowing, the engine will overheat. The procedure is then as follows: a Check that sea water circulation has failed by observing the exhaust. If it is gushing out (pulsing strongly is OK), the problem is in the inner coolant circuit and may be difficult to solve. If, as is more likely, water flow from the exhaust has stopped or has reduced to a trickle, check first that the sea water filter (sometimes called the ‘strainer’) is clear. Turn off the inlet seacock, then follow the pipe to the filter (this may be incorporated in the cock unit or may be remote), open the filter and clear the mesh. Reassemble, open the seacock, and go.


Seacock Skin fitting


Water trap Water pump


MANUAL OF SEAMANSHIP | 31


Power units


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