Understanding Marine Diesel Fuel

Trawler and motor yacht owners love the sound of our diesels; like sweet music to our ears. The diesel engines are the heart of any vessel.

But problems can take place with diesel fuel stored in your trawler’s fuel tanks, that will affect those diesel engines?

It is important to know what diesel fuel is to start with. Diesel fuel is refined from crude oil. In petroleum refineries, petroleum is heated, and different hydrocarbon molecules are extracted to create the fuel. Diesel is much thicker than petrol and vaporizes much more slowly. It's often referred to as "fuel oil" because of its consistency. Oftentimes forgotten, diesel is an organic matter.

"Give a diesel engine clean fuel and it will run forever and a day." This old saying is less of an exaggeration than you might think. Maintenance statistics show that ninety percent of trawler diesel engine problems result from fouled fuel. The promise of doing away with 9 out of 10 potential failures should put fuel-system maintenance at the top of your list.

The most common signs of fuel contamination in a boat are blocked filters, and reduced engine performance. However, the absence of these conditions does not necessarily suggest that your diesel fuel is not contaminated. In fact, it is probable that every trawler’s fuel is somewhat contaminated. Diesel Fuel pick-up tubes, where the diesel engine draws fuel from the tank, typically sit about 3/4 of an inch off the bottom of your fuel tank floor. This placement is designed to protect the engine from contamination that has fallen to the bottom of the fuel tank. Therefore, you may never realize that you have a diesel fuel contamination problem until the fuel is disturbed in some way - such as when you are in rough seas in your trawler.

Water can get into trawler fuel tanks in several ways – by condensation of humid outside air, during transport from refineries to distributors, by leakage from faulty fill pipes or vents and by sloppy handling. Water can cause injector nozzle and pump corrosion, microorganism development and fuel filter blockage with organic matter resulting from the corrosion or microbial growth. Your trawler’s fuel/water seperators should be checked frequently for water and drained as necessary. In freezing northern winters, ice formation in fuels containing water creates severe fuel line and filter plugging problems. Routinely getting rid of the water is the most effective way of preventing this problem; however, small quantities of alcohol may be used on an emergency basis to prevent fuel line and filter freeze-ups.

Frequent diesel fuel filter exchanges and the expensive and time consuming task of cleaning diesel fuel tanks have become acceptable periodic maintenance instead of looking for a warning signal for diesel engine failure. Diesel fuel filter elements should last several hundred hours or more and injectors some 15,000 hours. However, since diesel fuel is inherently unstable, solids begin to take shape and the gathering storage tank sludge will finally clog your diesel fuel filters, possibly ruin your injectors and cause diesel engines to smoke.

Diesel Fuel stored in trawler tanks for extended periods (6 months and more) requires special care. This diesel suffers from multiple problems that influence its quality. The presence of free water provides the platform for microbiological development that result in the formation of slime and acids causing corrosion of metal surfaces such as storage tanks, pumps, injectors, etc. Left unattended this water layer will trap sludge and become the breeding ground for microbes, fungus, yeast and more. This poisonous mix creates acids that compromise the integrity of your tank, lines, pumps, fittings and worse, diesel machinery.

Another crucial agent leading to diesel fuel deterioration, is mechanical stress created by heat and pressure of pumps. Since most diesel engines return considerable amounts of fuel back to the tank, it is simple to see that the engine itself adds to fuel deterioration.

Bugs in the form of bacterium and fungus are present in all diesel fuels. Extended periods of fuel storage can create ideal opportunities for germs to grow in fuel tanks. The first suggestion of microbic contamination is mucous-like accumulations on fuel-filters. Microbes can only be removed from the fuel system by polishing or by forbidding their occurrences by use of a diesel fuel biocide such as BioBor. I highly recommend it.

Should you use diesel fuel additives? There are many of additives on the market nowadays that are designed to improve the performance and efficiency of diesel fuel. I opt to use Marvel Mystery Oil. Even So, if you use the proper additives, you can achieve peak performance from your diesel fuel every time.

Trawlers typically have primary fuel filters and a set of secondary filters installed; Racor is a good example of primary filters. Every time the diesel engine is operated, the diesel is polished by filtering and returning fuel back to the tanks. A separate polishing system can also be set up that polishes the fuel independently of the engine operating.