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Fuel p­roduction often source of diesel engine problems


Over the past few years, there has been a sudden, dramatic and worldwide increase in filter clogging tendencies in engines. What has changed?

Oil supply and environmental concerns have resulted in important changes in fuel production, such as cracking techniques, blending formulas, ultra-low-sulfur fuel standards, and the introduction of biofuels.

These changes have altered the inherent stability of diesel fuel and significantly shortened its shelf life. Diesel is a complex fluid. It is not homogenous, and no two batches will ever be identical.

Fuel deterioration, filterability and shelf life depend on a variety of factors, including good housekeeping. The breakdown of fuel is also dramatically accelerated by the presence of water, microbial contamination, and exposure to heat and pressure from the engine’s fuel injection system.

The fact is that 80 percent of diesel engine performance problems start in the fuel tank.

Accelerated fuel degradation, which shortens fuel shelf life, depends on a series of factors:

* Contamination during transportation and storage

* Natural oxidation and breakdown

* The source of the crude oil

* Use of additives at the refinery

* Use of biodiesel blended with petroleum-based diesel, and

* Fuel temperature changes.

Not all fuel sent to a diesel engine is burned. A portion of the supplied fuel will flow past the injectors and back into the tank. As this unused diesel passes through the fuel system, it is heated by the hot engine and then returned to the tank. This hot fuel accelerates fuel breakdown in the tank.

Think about the experiments you did in high school biology class. In order to make bacteria and mold grow in the petri dish, it was put in an incubator. In the case of a yacht, the fuel tank becomes the incubator as the hot, returned fuel warms the rest of the fuel in the tank.

It then becomes the perfect medium for bacteria and fungi to grow. Both hot return fuel and condensation within the tank are important contributors to bad fuel aboard a yacht.

In addition, the U.S. Environmental Protection Agency (EPA) report on the use of marine diesel fuel identified a number of concerns with the diesel supplied to recreational vessels.

“Commercial marine businesses have the higher volume and cost incentives to arrange deals with refiners to produce tailored marine fuels …. In contrast to commercial marine businesses, recreational boat owners have no volume leverage and less cost incentives to arrange for special fuels. With the large overlap in boiling range with other (diesel) distillate fuels, the sources of recreational marine fuels are often land-based fuels. … Distributors of recreational fuels take what is most available, which is truck and tractor diesel fuel and home heating fuel. Both of these fuel grades are given the designation ‘Number 2’ fuel. All marinas and all fuel suppliers have reported that diesel fuel is delivered to marinas by tank truck, and the fuel is the same as provided to 
either on-road service stations or off-road supply stations.”

Aboard a yacht, the lack of fuel testing and an inadequate fuel maintenance program can result in the rapid breakdown and contamination of the diesel stored in the fuel tanks. Although there are commercial additives that can treat the symptoms of poor quality fuel, the problem doesn’t go away. It just gets masked temporarily and will soon resurface. Left untreated, it can cause engine failure.

Diesel fuel requires an active treatment process that will not only mitigate the effects of natural fuel degradation, but also remove contaminants and improve the fuel quality.

The major steps to assure optimal fuel quality are:

* Sampling and testing to assess the quality of fuel in the tank

* Filtration to remove organic and inorganic particles

* Separation to remove water from the fuel

* Polishing and conditioning to optimize the fuel itself, and

* Using additives to enhance the shelf life of the fuel.

Water, bacteria, sludge and dirt contaminate diesel fuel every step of the way, from the time it leaves the refinery to the time it is bunkered onto a yacht. Developing and adhering to a preventive maintenance for diesel fuel is the tried and true method of avoiding the most costly engine repairs.

Capt. Jeff Werner has been in yachting for almost 25 years. Contact him through

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