The Triton


Fuel turnover does not ensure cleanliness


Diesel Digest: Capt. Jeff Werner

Fuel degradation is commonly associated with the amount of time fuel has been sitting in a yacht’s tank. The assumption is that a “dock queen” will have more fuel problems than a yacht with an active cruising schedule.

Although there is some truth to this, it isn’t the whole story. In fact, fuel is at high risk of contamination well before it reaches its final destination aboard a yacht and is primed to accelerate fuel degradation when delivered.

It’s easy to assume that in a full tank aboard a vessel the fuel quality is up to standard, especially just after bunkering was completed. After all, there was “new” fuel used to top off the tank, so it must be clean, right? Not necessarily. Regardless of how fast fuel is being consumed, there is a good chance the “new” fuel may already be contaminated.

Fueling diesel.

Unless otherwise brought up to specification through a fuel maintenance program once it leaves the refinery, all fuel accumulates sludge, water and debris during the delivery process. Since the path diesel fuel takes along the supply chain is not recorded, there really isn’t a way to know what the fuel was exposed to prior to being pumped aboard. Was this fuel maintained properly? Was there water in the storage tank at the tank farm? Was sludge forming in the aboveground dispensing tank at the marina? These are questions that often go answered.

Taking on fuel of unknown quality should raise concern, as it may introduce more particulate, water and organic debris while stirring up old contaminants at the bottom of the tank. This contamination is what clogs fuel filters, destroys injectors, eats away at the fuel system, and robs engines of critical power, performance and, most important, reliability.

When water is present in fuel, fungi and microbes feed off the hydrocarbons in the fuel and bloom. This growth not only clogs filters, but its by product is acidic, promoting tank corrosion.

All diesel fuel contains wax. These waxes will crystallize when a yacht is operated in colder climates, which can contribute to premature filter blockage.

Solid particles such as dirt, rust and dust, cause damage to fuel system components through direct abrasive wear and erosion. This abrasive wear can ruin an injector’s ability to properly atomize fuel.

Sludge is a combination of different particulates, including organic and inorganic compounds, waxes and microbes.

To identify a problem with fuel stored on board, begin with a fuel maintenance program that includes fuel quality verification. If fuel quality verification it is not part of the plan, add it.

There is a series of simple, quick procedures that can identify any existing problem:

  • Visual Inspection. Look for potential entry points for contamination, such as deck fills that don’t seal properly or dry rotted seals on the tank.
  • Fuel Sampling. Taking samples from multiple locations within the tank will provide a good representation of the fuel. Most importantly, samples should be taken from the bottom of the tank, as this is the worst area. A hand pump, or submersible sample thief, is the ideal means of taking a sample.
  • Water Finding Paste. This can help quickly determine if water is present at the bottom of a tank.
  • Microbial Testing. Knowing something is growing in stored fuel will help identify the type of problem the fuel is facing.

There are many factors that can interfere with fuel quality, and going through a lot of fuel does not reduce the risk of contamination. Keep in mind that new fuel may be contaminated, the old fuel may contain particulates or debris, and the fuel tank itself may be affected by corrosion.

The only way to know for sure is to verify fuel quality, check the condition of the fuel tank, and take appropriate measures to correct any problems. Minutes of time in verification and  prevention processes can save thousands of dollars in repair costs and weeks of downtime.

Capt. Jeff Werner has been in yachting for almost 25 years, and is the owner of Diesel Doctor ( All Triton readers receive a 10 percent discount on online orders. Comments are welcome at

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2 thoughts on “Fuel turnover does not ensure cleanliness

  1. John Seagraves

    No where was fuel polishing either thru filter medium or a centrifuge mentioned.

  2. Lucy Chabot Reed

    A reply from the author:
    Thank you for your comments. This article was specifically written to about how to identify existing problems in a diesel fuel tank. The first part of a fuel preventive maintenance program is sampling and testing. Once the problems are accurately identified then fuel polishing and tank cleaning are the next step in the maintenance process.

    If you are a regular reader of the Diesel Digest column, you will find that at least 50% of the articles written cover the subject of fuel polishing in the greater detail which you may be interested in. Please check through the Triton archives for access to those columns. And you can always contact me at 239-246-6810.

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