Diesel bug blocks filters

What is Diesel Bug? 

Diesel bug blocks your filters, but what exactly is it?

You have no doubt heard of diesel bug, perhaps you even have it in your filters.  Understanding exactly what diesel bug is will help you understand how you can stop it from ruining your engine.

Diesel fuel is organic, so it provides an ideal environment for microscopic fungi, yeast and bacteria to feed and grow.  There are hundreds of different yeasts, fungi and bacteria around and fuel will absorb them from the air.  A combination of any can lead to the microbial infection that is commonly known as ‘diesel bug’.  So the bug is a combination of fungi, yeast and bacteria.

Diesel Bug multiplies quickly.  Doubling in size every twenty minutes a single cell weighing just one millionth of a gram can grow into a biomass of 10 kilograms in just 12 hours.  It doesn’t take long at all for a thick biomass of diesel bug to become centimetres thick. 

Perfect Environment for 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 Cure

Depending on how bad the diesel bug infestation is, it may be that a simple shot of broad spectrum biocide will do the job, initially; however, as diesel bug is becoming more problematic due to low sulphur and more water finding its way into fuel, you might want to consider a system for removing the water from fuel permanently.  If you think you have a serious infestation of diesel bug then you need to drain and clean your tank and fuel systems before refuelling.  Once again as water is present in all fuel and a biocide cannot remove water you should seriously consider implementing a system to remove the water from your fuel as part of an overall maintenance strategy.

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Peter weide Director MarShip UK

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.

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Diesel bug lives in water
Diesel bug lives in the layer between water and fuel