What is Diesel Bug? 

Your diesel fuel tank provides the perfect environment for diesel bug to thrive.  Your fuel tanks provide water in which it lives and breeds, carbon in the fuel on which it feeds and oxygen and sulphur for respiration together with trace elements for growth.

These pesky invaders don’t just clog up your filters and put you at risk from a fuel related breakdown,  they can form bio-films on steel surfaces that are corrosive.  Look for the tell-tale pits and crevices on your tank and if there’s a smell of rotten-eggs then you know you have a serious diesel bug problem.

Why Biocides Won't Solve the Diesel Bug Problem

So the answer you would think is simple, dose the tank with a biocide, well that might kill the current diesel bug infestation, but what about when you next fill up? The bugs themselves can hide, lying dormant in the minute crevices of the metal, rubber and polyurethane coatings of fuel tanks and systems.  Then as soon as water is introduced again (i.e next time you take on fuel) the diesel bug infestation can take hold once more.  So, while dosing with biocide is an option you may find it both time consuming and expensive as you have to treat each new intake of fuel separately.

Prevention is Better than Cure

The best way to ensure your diesel stays free from diesel bug is to remove the habitat diesel bugs thrives in– the water.  Water is present in all fuel and by removing water from your diesel  you remove their home and breeding ground.  Without water, diesel bug has nowhere to live. The best way to remove water from the fuel is to fit a Diesel Dipper® The Dipper gets to the very bottom of the fuel tank, below the fuel suction removing water, sludge and diesel bug leaving the bottom of the tank clean and dry.

The Cure

Depending on how bad the diesel bug infestation is, it may be that a simple shot of broad spectrum biocide like DieselAid® B will do the job. But be aware that it is important to remove the water, this cannot be stressed enough. This can be by simply draining out from the drain plug regularly, if you don't have a drain plug then use a Diesel Dipper with a Dip Tube to get to the bottom.
Many engines have filter/water separators between the tank and the engine, however if you are finding water and sludge in these filters then it's clear that there is already a layer of sludge and water on the bottom of the tank. The average fuel suction from a diesel tank is always at least 10-20 mm off the bottom of the tank...because the tank manufacturers know that there is always sludge and water on the bottom of the tank.
Be careful of enzyme additives that claim to remove the water, they do this by enabling the water to be absorbed into the fuel. That was fine with engines in the past, today's modern common rail diesel engine needs clean DRY fuel. any dissolved or saturated water in the fuel can have serious expensive consequences. This is the reason all engines now have water alarms in the fuel filters which forces the engine into "limp home mode".
We know one of these enzyme type additives, if not mixed in the fuel properly, can also form a jelly like substance on the bottom of the tank which go onto block filters.
Our advise is remove the water mechanically by draining or with a Diesel Dipper and dose with a biocide.

Peter Weide is MD of MarShip, a UK based company specializing in optimising the efficiency of marine diesel engines. Advising on maintaining the cleanliness of Air, Fuel and Lubricating oil, we regularly recommend solutions to operators and appear regularly in industry press, with our full range of diesel additives DieselAid we can offer solutions for most operating conditions and wont advise them if you don’t need them.