Diesel bug is the colloquial name for the microbial growth that lives and feeds on diesel contaminated with water. In small quantities it’s relatively harmless, but a serious case will clog up your boat’s fuel filters faster than you can replace them.
Diesel bug has become more prevalent since an EU directive was introduced, encouraging suppliers to add up to 7% biodiesel to their standard diesel. This is because biodiesel is hygroscopic, meaning it holds and attracts water.
How you treat diesel bug depends on the level of contamination. If it’s relatively minor, you may get away with dosing your fuel tanks with a proprietary diesel bug biocide. This kills the bug but does not remove it, so you’re relying on your existing filters to trap the residue without blocking them completely.
A better solution is to have the fuel professionally polished. This involves sucking the fuel out of your boat’s tank, spinning and filtering it to remove the bug, then pumping it back in.
However, this still won’t get rid of built-up sediment in the tank. The only sure way of removing everything is to steam clean the tank through an inspection
hatch (or have one cut into it). This can be a costly and time-consuming exercise.
The alternative is to fit a permanent fuel-purifying system to your boat, which is effectively a small built-in fuel-polishing system that cleans the fuel coming out of
your tank before it reaches the filters.
For most of us, though, the easiest solution is to avoid getting the bug in the first place. There is no silver bullet, as there is always the risk of taking on contaminated
fuel from an unreliable source, but our video covers some simple steps you can take to reduce the likelihood of getting the bug in your system and preventing it developing into a problem.
Jon Mendez delivers a step-by-step guide on how to change the primary and secondary filters on a diesel engine
In this video Nick Burnham guides you through what to look out for when you sea trial a boat
Jon Mendez guides you through how best to rig an effective anchor set-up
MBY's definitive guide to all those essential tasks you need to know how to do but were too afraid to…
In the first of our 12-part maintenance series, Nick Burnham guides you through the best techniques to clean your teak…