TESTED


12 diesel bug treatments


Diesel bug can clog fi lters and starve your boat engine of fuel just when you need it most. Can diesel bug treatments kill it off? We test 12 to fi nd out


often more by luck than judgement, but with the introduction of biodiesel (often referred to as FAME – Fatty Acid Methyl Ester fuels) and biodiesel mixtures the slice of luck required to avoid diesel bug is going to need to be a lot bigger. Diesel bug is a general term for a


T


host of fungi, bacteria and yeasts ready and willing to inhabit your tank, whether by transfer from infected fuel or by colonisation from airborne spores. Around 147 species have been identifi ed living in infected non-bio diesel fuel, but the new fuels bring a whole host of new organisms to join the party – over 1,400 at the last count. It makes sense when you think


ales of diesel bug can seem overstated to some of us. Many boaters have evaded the problem for years,


about it: the biofuel additive might have elements of fi sh oil, rapeseed oil, vegetable oil, animal fat – almost anything. Adding all these extra oils makes the fuel attractive to many more kinds of microbial life by offering a more varied diet. Diesel bug thrives at the interface between fuel and water – ie just off the bottom of the tank, where the micro-organisms form colonies. In this cosy environment they break down the alkanes in the fuel using oxygen from the water, precipitating a black sludge to the bottom of the tank as they do so.


This sludge is formed from the microbes’ excretions and from badly


emulsifi ed fuel,


and consists in part of thread-like compounds a few microns (micrometers) in size that quickly agglomerate to block fuel fi lters and stop your engine.


HOW CAN YOU


FIGHT DIESEL BUG? The best weapon we have against all these organisms is their


common factor: habitat. If there is no water in the tank, diesel bug cannot survive. In reality, it’s impossible to prevent water entering your tank – tanks will suffer from


condensation at the very


least, even if you manage to avoid any


water entering through the


fi ller. However,


you can limit the condensation by keeping your tanks topped up to minimise the volume of damp air in the top of the tank, and by regularly draining off the water and debris from the bottom of the tank. If your tank doesn’t have a drain cock at the bottom, fi t one at the lowest point, with a valve to allow you to run off fuel into a glass jar. When it runs pure, your tank is clean again. Maintenance such as this can


help keep your tank clean, but if you pick up diesel bug you will need to eradicate it. Additives are available, which split into two types: biocides and dispersants. Both rely on the bug’s reliance on water: biocides by dehydrating the cells or blocking their ability to feed, and dispersants by lifting the water into suspension, destroying the micro-organisms’ environment. They will then either starve or be burned in the engine, together with


Practical Boat Owner 534 May 2011 • www.pbo.co.uk


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