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Diesel bug treatments

FAME and sulphur

This test is about diesel bug, but other problems from the new FAME (biodiesel) mixtures and low-sulphur fuels are often referred to in the same context.

n Up to 7% FAME can be mixed with road diesel, but even this is enough that some adverse effects are being seen. One of the worst is the cold fi lter plugging point (CFPP), the lowest temperature at which fuel will pass through a specifi c fi lter. For non-bio diesel this is between -7°C and -14°C, but for FAME mixtures it can be as high as 1°C – bad news for winter sailing. At present none of the additives in EN590 DERV – the fuel supplied to garage forecourts – address this. A kerosene-based treatment such as Soltron or Star Tron will help, so if you sail in the winter is a point worth considering.

n Adding FAME has been shown to loosen debris and cause it to be washed through your fuel system. The fi lters should cope with this, but keep an eye on them and be prepared to change them more frequently until the system settles down again.

n FAME will attack rubber and cause it to degrade over time, but a more immediate issue is that seals which have swollen in traditional hydrocarbon fuel can start to shrink and cause leaks. This is likely to affect seals older than about eight or 10 years, so if your engine falls into this category keep a careful eye out and keep plenty of spares.


180 160 140 120 100 80 60 40 20 0

Filtration time (seconds) 154 106 86 88 89 86 98 82 93 78 95 81 111

Percentage of diesel bug killed after 10 days

100 80 60

40 20

0 87 96 97 96 92 79 80 79 96 98 71



The good news for boat owners is that, whichever of these products you use, it will have a positive effect. But some are better than others, and some are more suitable for continued use. Firstly, there’s a big difference

n Modern fuels also have a reduced sulphur content, which reduces their lubricity. The good news is that the additives in EN590 DERV meet a set standard which should bring the fuel’s lubricity back to a level that will avoid harm to your engine. Even better, EN590 should give slightly more power for slightly lower fuel consumption.

between biocides and dispersants. Biocides are excellent at giving contaminated tanks a shock treatment and killing diesel bug, but often struggle to shift by-products and get rid of water. Dispersant treatments are slower at getting rid of the bug but have the benefi t that they lift the water and much of the debris into suspension, so with perhaps a couple of fi lter replacements you stand a better chance of cleaning your tank. So which should you use? A

biocide will quickly and effectively kill the problem, and from our results and observations it’s hard to choose between

Practical Boat Owner 534 May 2011 •

Grotamar 82, Wasp Biokem, Marine 16 and Eradicate. All of them had excellent kill rates, although Grotamar has the edge for fi lterability and Wasp for kill rate and price (for a shock dose). For ongoing maintenance. Fuel

Doctor would work well but is expensive, even in the smaller dose. Soltron and Star Tron have similar enzyme formulations which are both particularly good at improving fi lterability and would be good choices, especially if you use your boat regularly. Fuel Set didn’t have the best kill rate or fi ltration results but had excellent water and debris dispersal. It’s also quick. There seems little doubt that

with the introduction of biofuel mixtures, more boat owners are going to struggle with diesel bug. But it’s something we’re going to have to deal with and get used to, because it’s here to stay.

Choose a dispersant treatment for ongoing maintenance

While FAME-free fuel is still permitted for coastal shipping, supply may well become scarce for small boats so the likelihood is that we will all have to put FAME into our tanks at some point. Perhaps it’s time to give your engine and fuel system a thorough service, clean it well, change the seals and keep a careful eye out for the dreaded bug, confi dent in the knowledge that there are some effective products ready for combat if and when it comes to call.

Percentage cATP reduction

Time in seconds to fi lter 500ml of fuel

Sart Brite Biodiesel

Fortron Fuel Doctor Eradicate Marine 16 Grotamar 82 Fuel Set Soltron Kathon Star Tron Wasp Biokem

Diesel Plus Control


The control sample showed a growth in cATP of 12% over 10 days

Sart Brite Biodiesel

Fortron Fuel Doctor Eradicate Marine 16 Grotamar 82 Fuel Set Soltron Kathon Star Tron Wasp Biokem

Diesel Plus Control


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