It is critical to check any fuel entering the tank, especially if the source may be of poor quality. James Devoy investigates marine diesel engine problems

The blockade of the past two years has led to more and more yachts being shelved and left unattended around the world. The scramble to return home before travel restrictions begin in 2020 means that some sailors have to abandon the ship as much as possible or risk being trapped.

Even the cruisers staying on the yacht often find themselves unable to move around in the dock. Limitations in many areas still exist, and remote organization maintenance can be challenging. This has caused more and more ship owners to return to their yachts to find a thorny problem: diesel bugs.

Diesel bugs are a mixture of different microorganisms, bacteria and fungi. They can live and multiply at the interface between the water in the fuel tank and the diesel. Like most bacteria, it multiplies quickly and can become a serious problem in a short time. It particularly likes warm weather, but it can happen anywhere.

Once in your engine, "errors" can cause problems in almost every part of the engine, increasing fuel consumption, clogging filters and reducing fuel flow until it stops.

The introduction of biofuel or FAME (Fatty Acid Methyl Ester Fuel) into marine diesel makes the worm an easier source of food. Because the sources of biofuels are so diverse—from fish oil and rapeseed to fats in fast-food fryer, almost everything—there are plenty of new bugs craving it.

Knowing how to replace the fuel filter is the first step in getting your engine to run again when it gets clogged by diesel bugs. Photo: Thor Johnson

Biofuels are hygroscopic (that is, they absorb moisture from the air over time), and it is this moisture that makes diesel bugs thrive. To date, more than 1,500 species of diesel bugs have been found. In recent decades, reducing sulfur in fuel has been necessary to reduce the environmental damage of marine diesel, but this problem has been exacerbated by creating a much less corrosive environment for bugs.

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Diesel bugs can be brought into your fuel tank from an infected fuel source, but they can also live in the air to be absorbed into biofuels. Filter changes and regular use will generally reduce the level of infection, but if the engine is not used for a long time or does not provide services, it may create an environment for vulnerabilities.

Diesel bugs can appear as a thin carpet of sludge. Photo: marine16.co.uk

Diesel bug microorganisms appear as brown slime in your fuel tank, but they can also be seen as black particles in your filter bowl. A good filter should be able to prevent most errors from entering your engine, but none is perfect. At sea you may not have enough filters to replace all clogged filters.

Despite the dual-fuel filtration system, Nichola Wright was on the way from Ibiza to Mallorca due to a diesel engine failure and met on her Kelly Peterson 44 In the case of a sudden engine shutdown. "We were surprised to encounter this problem because we have been using air conditioners to dispose of the diesel we bought," she explained. "Maybe this is the result of the long layup in the winter-we stayed at the dock for eight months due to Covid. The engine has not been used during that time, the fuel is left in the tank, and the fuel is filled up for processing."

Modern diesel fuel is highly refined and begins to decompose after 6-12 months. This is when the danger of diesel bugs begins. Since water is denser than diesel, it will sink to the bottom, allowing bugs to better avoid any cursory inspections.

Viki Moore is a cruising sailor stationed in New Zealand. Her Young 88 Wildwood also encountered persistent diesel bug problems. After replacing many filters, this error caused the engine to malfunction at a critical moment: "It blows about 25 knots on the nose, and we weave the way to the cradle among the abandoned dock piles," she Recalled.

"When the motor was out of power, we were about 200m away from the intended destination. The wind was whistling in my ears and the sails were stowed in winter, and we began to be quickly blown back to the rocks. I panicked and pressed the engine start button frantically, but nothing Any response. Thankfully, my crew casually walked to the bow and cast the anchor aside.

"We are safe, but we are trapped. There is no motor, no windlass to help withdraw the anchor, confidence is hit, and there is no appetite to open the sails and try to bypass the old pier piles around us. We have no choice but to Put down and turn on the kettle, waiting for rescue."

After being safely towed to the berth, Moore was able to assess the problem, but the location of the water tank meant that it would eventually have to be cut out of Wildwood and then steam cleaned and modified by experts.

As the first preventive measure to avoid diesel bugs, make sure to seal tightly on well-installed fuel tank caps to prevent rainwater and salt water from entering. Keeping the fuel tank full can also reduce the chance of condensation in the fuel tank.

Peter Weide is a former marine engineer and a director of Marine 16 and MarShip, two companies specializing in providing chemical and mechanical solutions to the diesel bug problem. We asked him for his advice on using fuel additives to help prevent or kill diesel worm infections:

"This is a broad subject and depends on how long you store diesel fuel. Fuel additives should at least contain lubrication improvers and detergents.

When replacing the filter, it is also worthwhile to check the fuel line connection for sludge. Photo: Nicola Wright

"There are some additives based on old technology that allow free water at the bottom of the fuel tank to be absorbed into the fuel body and pass the engine'safely'. This was great decades ago, but if you put saturated diesel into a modern common rail engine, You will definitely encounter very expensive engine problems.

"All tanks must breathe, and water will come in. Sooner or later the water will come to diesel bugs. So get rid of the water and use a "maintenance dose" of biocide, which will kill them before they appear."

Dominic Heydon and Carly James struggled with this error on their Trident Warrior 38 Cadoha (see youtube.com/SailingCadoha). They tried different methods to solve the problem. "We consulted forums and YouTube videos before being pointed to a'fuel buffing' man who came forward to'clean up our system', worth £600!"

Nichola Wright's clogged filter (left) compared to a new filter after a long layup. Photo: Nicola Wright

"I showed him the location of our two fuel tanks. He said that the fuel tanks were too tight and he couldn't reach in for cleaning, but he could still polish the fuel."

Although the bugs had been eliminated, their baffle tank was still clogged with mucus, so they turned to mechanical solutions to clean the areas hidden by the baffle. Diesel Dipper is a small modified filter that can draw fuel from the bottom of the tank and separate any remaining water and diesel bugs, which means it can reduce the chance of re-infection and clean the fuel in the tank.

"Whenever we turn on the engine, we will run Dipper, especially when we are in a bumpy sea lane, we will turn it on," Heydon explained.

"The more we use Dipper, the smaller the'sludge' in the sample. It seems to be weakening everything there, managing the situation, but the most important thing (for us) is to prevent the engine from getting clogged and failing. "

There are several insecticides on the market that are designed to kill diesel bugs, but once they die, they still leave residues in the fuel tank. Bones Black, a marine engineer, global sailor and captain of chartered yacht Emily Morgan (see Yachtemilymorgan.com), shared his tips on how to clean the fuel tank:

"Almost all fuel is pumped from the tank into a clean tank through a high-quality filtration system, and they can be hired or sent to pump out for you.

"Leave a centimeter of fuel at the bottom and use it to clean the rest of the tank. Most baffles shouldn’t reach the top of the tank, so you can reach every part and scrub with the dishwashing brush on a stick, even The toilet brush purchased for this purpose!

"After scrubbing all the surfaces and corners of the fuel tank, place absorbent pads on the bottom until it absorbs all the fuel residue; we use diapers because they are cheap and they work well. They also have a plastic outer surface so they can be picked up and Put it in an airtight bag, there will be almost no mess. Finally, clean it with a high-quality rag and wipe it dry."

If you are caught by bugs during the voyage, Black recommends short-term repair measures to allow you to return to the shore safely: "If you can’t use the [fuel] tank, you can put a can of clean fuel next to the engine from the outlet of the fuel water filter Remove the water inlet pipe, put it in the tank, and start the engine directly from the fuel tank to let you go home."

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