I recently attended a technical paper on "diesel bugs" as they are commonly known, given by a gentleman from UK who researches such matters. He related an incident that he had recently with his new diesel vehicle when refuelling at quote a major supermarket netwrok that sells its own brand fuel unquote. They sell the new ultra-low-sulphur-diesel mandated by the EU for next year, including the bio-fuel proportion.

His problem appeared to be that his car fuelling pipe kept blowing back and triggering the handpiece shut-off, so he went back to the supplier and complained. Not so, says the supplier after trials, so back to the supermarket. Using his credentials, he got to be present when the supply lines were opened up. UGH !! The filters were blocked with gunge that resembled yellowish grease. In his laboratory, the stuff turned out to be yeast which had violently multiplied. Investigation showed that yeasts love bio-fuels and, in the presence of only a small amount of moisture [ far less than the usual diesel bugs,] the yeasts multiply.

The deposits had turned inside-out a witches-hat filter that normally sat apex towards the incoming flow, and blocked the final filter in the handpiece. It was that final blockage that was triggering the handpiece shut-off.

He expressed concern at the possible results of the gunge getting into the ever-increasing pressures in common-rail injection systems. At present, the only really safe escape after such contamination is a full strip-out , clean, and sterilise. Because different yeasts enjoy different bio-fuels [ cooking oil, corn oil, rape-seed oil, etc.], there is not yet a chemical bug-killer that covers all yeasts.

Why has it not come to notice earlier ? Although not proven, the research suggests that a proportion of sulphur acts at least as a restraining mechnism on the yeast multiplication rate. [ That is suggested as the reason why the big container ships with their cathedral diesels burning 5% sulphur fuel have almost no diesel bug problem ]

Diesel drivers may wish to keep this knowledge stored away in case you suddenly have trouble filling up.