“Diesel bug” describes microorganisms that can grow where fuel and water meet. Their biomass and by-products create slime, sediment, filter blockage and corrosion. Water can enter through contaminated supply, a poor deck-fill seal, vent arrangement, condensation or a leaking tank component.
Warning signs
- Dark slime or strings in filter bowls
- Repeated filter blockage
- Water or sediment drained from the separator
- Engine surging or losing power in rough water
- Tank corrosion or pinhole leaks
- Contamination appearing soon after refuelling
Treatment must match the problem. Drain free water, inspect and physically clean accessible tanks when contamination is established, replace blocked filters and dispose of waste correctly. Fuel polishing can remove suspended contamination but may not reach material stuck behind baffles or repair the source of water.
Biocides must be approved for the fuel and engine, dosed exactly and handled safely. Killing organisms can release more debris and block filters. Carry extra elements and monitor restriction after treatment.
In humid Australian conditions, sample the tank bottom periodically and inspect deck-fill O-rings and vents. Buy fuel from a reliable high-turnover source where possible and use a clean transfer method from jerry cans.