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Engine Room

New technology lets engineers test fuel onboard


The cornerstones of a diesel fuel preventive maintenance program are: sampling and testing to assess the quality of fuel in the tank, separation to remove water from the fuel, filtration to remove organic and inorganic particles, polishing and conditioning to optimize the fuel itself, and using additives to enhance the shelf life of the fuel.

The initial preventive maintenance step is sampling and testing. But testing for what? The major contaminant in diesel fuel is microbes. Testing for microbial growth determines the presence of bacteria, mold, fungi and the size of the colonies.

Until recently, there have been two methods used to test for microbes. The first involves sending a fuel sample via overnight express to a testing lab. A culture study is then completed, which requires 48-72 hours of incubation to determine the type and level of infestation. The result is either a negative or positive report for the presence of fungus or aerobic bacteria and how many colonies exist. On the average it will take a minimum of four days to receive the final results from the lab. In addition, there is no guarantee that the chain of custody has not been breached or that the sample has not been compromised.

The second method is an off-the-shelf kit, such as Liqui-Cult. The user injects a small amount of fuel with a syringe into a bottle that contains a testing fluid. Just shake it up and wait … 30 hours for bacteria to grow and 72 hours for fungal growth. No shipping and handling is involved. The time delay is still a factor, and the results are just a general “yes” or “no” for bacteria and fungi, rather than targeted to the specific microbes most commonly associated with diesel fuel contamination.

What if a testing method existed for diesel fuel that was as quick and simple as a pregnancy test kit purchased at the corner pharmacy? That is the exact market niche filled by FuelStat, an on-site kit that tests for organic contaminants with observable results in 10 minutes. The key difference between FuelStat and other fuel testing methods is that it uses immunoassay techniques.

According to company materials: “This means that it detects contamination by ‘finding’ material that is produced by the three different types of contaminants that grow in fuel. Therefore, there is no need to capture a part of the living organism and grow it up … . The objective of the test is to provide rapid screening of fuel samples, giving a quick and accurate assessment of H.res, bacteria, and other fungi including yeasts in the fuel tank.”

Hormoconis resinae, abbreviated as H.res, is the primary fungus that causes filament-like contamination in diesel tanks, and it is the most damaging as well. “When compared to single cell yeasts and bacteria, H.res produces far more biomass and is thus more likely to cause blockage problems in filters and fuel lines. Secondly, it is by far the most common cause of microbial corrosion in fuel tanks … . Thirdly, because of the way H.res grows at the interface between the fuel and water … it firmly attaches itself to the tank surface.”

Conidia Bioscience, based in the United Kingdom, has developed, engineered and patented FuelStat and devoted the past 10 years to refine this product for testing jet fuel (kerosene) in the aviation sector, and diesel fuel in the maritime and land sectors.

The FuelStat test “measures the amount of contamination by H.res, bacteria and fungi actively growing in the sample and reports that as the weight of material in the sample. The test provides results based on a traffic light scenario:

Negligible (green) – negligible contamination

Low Positive (amber) – moderate contamination

High Positive (red) – heavy contamination”

Conidia Bioscience has recently announced a smartphone app that will read the test results, determine the course of action to remedy the fuel problem, and keep a log of the tank testing history.

This new technology is the ideal method for testing diesel as part of a yacht’s monthly preventive maintenance program. FuelStat is now distributed in the United States by Busch and Company Resource Strategies, and can be sourced through my company, Diesel Doctor.


Capt. Jeff Werner is a 25-year veteran of the yachting industry as a captain on private and charter yachts, both sail and power, and a certified instructor for the RYA, MCA, USCG and US Sailing. He also owns Diesel Doctor ( Comments are welcome at


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2 thoughts on “New technology lets engineers test fuel onboard

  1. Edward Kane

    Capt. Jeff, thank you for mentioning our LiquiCult Test Kit. We just hit 30 years old! My father introduced it in 1990 and he would be elated just knowing that it was mentioned in your article. Thank you.
    We have plenty at our two office locations if they are needed! Our web site:

    I was a Captain too, US Army! Thank you sir!

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