Yanmar Pleasure Boat Marine Engine Help

Diesel ' Bug '

Microbiological organisms, Cladosporium resinae and Aspergillus fumigatus being but two of many, and commonly called 'DIESEL BUG', can grow at the interface between the WATER and the fuel. This organism can block fuel filters and bring you to a stop anywhere. It propagates quickly in warm, humid climates. These organisms generate acids that corrode highly polished metal surfaces, like the inside of fuel injection pumps and injectors, this can cause high fuel leakage past the plungers into the oil system. The oil system on the engine then becomes seriously diluted with diesel, which may show up as a crankshaft and/or main bearing failures amongst other things. This nasty little bug has been know to totally destroy large engines!
They also generate slime which blocks fuel filters and in severe cases, fuel lines.

How do I identify microbiological contamination?

The fuel is cloudy or a rusty color ( man, this is going to be bad ), the filters will appear to be slimy ( man that's bad ) or the filters are covered with a black jelly ( man, that's really bad! )

How do I get rid of it?

Drain all the fuel, including the lines, and replace the filters. Dispose of it in accordance with the local rules. If possible, steam clean the tank. Refill the tank completely with clean fuel.
Bleed the fuel system and go motoring. Any residual dead bug will be burned up in combustion.

How do I prevent it?

• Add a proprietary biocide to the fuel.
  Do not add more biocide than the manufacturer recommends! Usually 1 millilitre per litre of diesel.
  
• Use a ' Debug ' or other type of magnetic bug killer filter. These require the fuel to be pumped through them almost continuously to kill all the microorganisms. Boats that are used rarely may need a circulating pump to keep the fuel moving through the ' filter '.