Four Common Diesel Fuel Contaminants – And How to Get Rid of Them



We’ve written about bad fuel on this blog before. Bad, or dirty fuel is the number one service and mechanical problem our engines (or any other manufacturers’) engines face.

What makes for bad fuel?

Water: Water is the number one most common contaminant we find. Condensation or adulteration are the main causes. When boats sit idle for long periods of time, condensation, sometimes substantial amounts, builds up and enters the fuel. As to adulteration, this usually occurs as an attempt to disguise fuel theft.

Wax: This is often found when fuel theft is occurring. Specifically, paraffin. Paraffin can be burned by the engine, but when the fuel lines cool, it solidifies and can completely clog up the entire fuel system.

Rust and other Solids: Rust comes from condensation, leaking gaskets or seals on the engine, and other sources. Many times, the tanks at the bunker can be contaminated. Vessels that operate in extreme temperatures are often at greater risk from contamination by solids.

Micro Organisms: In the marine environment, micro organisms are always present, and easily contaminate fuel. The fill lines, leaky gaskets, or worn seals exacerbate the problem.

So, how are these problems avoided or rectified?

The most important step is not only replacing fuel filters, but sticking to the maintenance schedule as detailed in your manual (This includes gaskets and other parts impacted by wear and tear).

A oil / water separator can help with water contamination, as can draining the fuel tanks during extended storage or starting the engines and running them at least monthly.

Upgraded fuel filtration can help (See your dealer), as can the addition of bactericide or fungicide to remove micro organisms.

Periodically spot checking fuel at the bunker is also a good practice.

Finally, in areas where theft is a problem, proper management and vigilance is often more effective than mechanical means of control.