For all boat owners, be they sailors or power boaters, a reliable diesel engine is a prerequisite.  Clean diesel fuel is the single most important ingredient to keep your engine running smoothly and reliably.  According to injection pump manufacturers CAV, 90 percent of all diesel engine problems are caused by contaminated fuel.  In this article I will look at potential sources of fuel contamination, the damage contaminated fuel may cause to your engine, ways to prevent fuel contamination and fuel filtration systems to protect your engine. 

In tropical climates such as South East Asia the most common cause of fuel contamination is water, generally a result of condensation inside fuel storage tanks on board or at fuel depots on land.  Whenever you purchase diesel fuel you should consider the quality of the fuel.  Generally the best fuel can be found at the busiest suppliers as the fuel does not sit around long enough to accumulate water, sediments and bacteria.  Busy marinas, commercial fuel barges and service stations are the safest sources.  Here are some simple tips for fuelling and storing fuel -

       If possible filter fuel as it enters the yacht using a funnel with a fine mesh or similar.

       If using cans or drums to transport fuel ensure they are clean and dry before adding fuel.

       If taking fuel from a barrel, a clear tube lowered to the bottom of the barrel and then withdrawn with your thumb blocking the top will show up water or serious contamination.

       Whenever possible keep fuel tanks full to reduce condensation, this is especially true if the boat is to be left unused for any period of time.

       Ensure fuel breathers do not collect water.

       Check that filler caps have intact seals and are closed tightly as the last thing you want in your fuel tanks is salt water.

Fuel contamination can damage your engine in various ways.  Severe cases, especially those involving bacteria, can cause the filters to block, starving and even stopping the engine.  This generally happens at the most inconvenient times, leading to potentially hazardous and life threatening situations.  Water in fuel not only causes misfiring and loss of performance, but also destroys engine components by allowing rust to form inside the fuel system and can damage or even completely blow the tips off injectors by turning to steam.  Nigel Calder points out that a fuel injection pump is an incredibly precise piece of equipment which can be disabled by even microscopic pieces of dirt or traces of water.  It is also the single most expensive component on an engine.  Unlike other engine parts, injectors and the injector pump can rarely be repaired other than by specialists. 

The primary line of defense for marine diesel is the fuel filtration system.  ALL marine engines should have primary and secondary filtration, including a water trap.  Racor filters from Parker Hannifin are a good example of a typical primary filter.  Primary filters are generally in the 10-30 micron range and should include a centrifuge which spins off large solids and water droplets.  These will settle to the bottom of the collection bowl as they are heavier than diesel.  The filter element itself repels water, tiny solids, algae and rust.  In Thailand it pays to be vigilant and ensure the replacement filters you buy are genuine, saving money by buying copy fuel filters is a false economy.  Power boats benefit by having dual primary filters connected by valves so that filters can be changed without shutting down the engine.  A vacuum gauge between the primary filter and the lift pump is the best way to detect restriction in the filter.  Secondary filters are usually provided by the engine manufacturer and mounted on the engine itself.  They will be in the 2-10 micron range and often also have water collection bowls.  Both primary and secondary filters should have any water drained from the bowl on a regular basis.  Water sensors with a warning light or audible alarm are a sensible option for water separating filters.

Perhaps the most devastating fuel problem in the tropics is fuel bug.  Extreme cases can completely block fuel lines and valves with stringy, gooey gunk.  Fuel bug is a bacteria that grows in the interface between water and fuel, needing these elements and oxygen to reproduce.  Byproducts of their growth process include acids and fumes which can corrode pipes, valves and tanks. Fuel bug can be dealt with by discarding contaminated fuel and cleaning the tanks internally, treating with biocide or adding a permanent magnet type fuel treatment unit such as produced by New Zealand company De Bug Worldwide.  These devices use opposing magnets to kill the bacteria which are simple, single cell structures that have a positive and negative charge.  As the bugs pass around the magnets, twisting frantically, they literally blow themselves apart.  The units resemble a small fuel filter and are installed between the fuel tank and the primary filter.  They require no maintenance beyond draining contaminants, however in severe cases they may need to be dissembled for cleaning.  Biocide can be used to kill bug by dosing the fuel in your tanks however this can lead to a build up of bacterial sludge at the bottom of the tanks and blocked fuel filters whenever rough weather stirs this up.

Fuel polishing utilizing a transfer pump, a De-Bug unit and a water separating filter can greatly improve the condition of the fuel in your tanks.  Either a contractor is brought in to polish the fuel using portable equipment or better still a polishing system can be permanently installed on board.  Such a system will incorporate a DC pump so that stored fuel can be cleaned while the yacht is at the dock, ensuring that all fuel has passed the filter and De-Bug unit before going to sea.  This can dramatically reduce the occurrence of fuel problems at sea. 

It is clear that clean fuel is of critical importance to the health of your engine and likewise to trouble free motoring.  Perhaps now is the time to take a closer look at your fuel filter bowls and the condition of the fuel in your tanks.