Ask Sail: Running Rough and Dry

I have a Soverel with a small diesel engine that has sat idle for a couple of years without fuel stabilizer. The engine starts, but runs rough. There is also no discharge from the exhaust line.
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Doug Stephens asks via email:

I have a Soverel with a small diesel engine that has sat idle for a couple of years without fuel stabilizer. The engine starts, but runs rough. There is also no discharge from the exhaust line. The water-pump impeller was changed and appears to be turning properly. Any advice would be appreciated.

Nigel Calder replies:

The rough running and lack of raw-water discharge are probably unrelated. Diesel oil generally stores better than gasoline, so two-year-old fuel doesn’t bother me. However, there is likely some condensation in the fuel tank, so water in the fuel might be causing the rough running. Before running the engine again, check and change the fuel filters. If there is any water in the filters, drain off the fuel from the very bottom of the tank, which will probably require that you insert a tube from above to pump it out. Also check the air inlet and exhaust system for obstructions. If you’ve got clean fuel and unobstructed air/exhaust flow and the engine still runs roughly, you may have a more serious problem such as a stuck valve or malfunctioning injector.
As for the lack of raw-water flow, you need to work your way through the whole system from the seacock to the injection point into the exhaust. Things to look for: a closed seacock; a collapsed or kinked suction hose; a plugged raw-water strainer; an air leak into the strainer (if it’s above the waterline); wear in the raw-water pump that allows air to get past the impeller blades, thus air-locking the system; obstructions in the heat exchanger (though these are unlikely to completely block the flow); or an obstruction at the injection point into the exhaust.

NigelCalder

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