DIESEL Fuel bugs

By: Rosmac  05-Apr-2012

DIESEL Fuel "bugs" are actually Cyanobacteria, which live in the diesel / water interface . not to be confused with asphaltene chemical sludge compounds.


All diesel fuels contain micro-organisms (commonly called "bugs") and when the conditions are favourable the "bugs" will rapidly grow.  Both "bugs" and asphaltenes (old diesel sludges) can cause fuel filters to block., with subsequent engine malfunction, or worse still, engine stoppage.  Removing water from fuel tanks and keeping the fuel fresh goes a long way to controlling the problem.  Other steps that can be taken to control "bug" growth is using a good quality diesel additive such as , or a specific biocide and a proven magnetic unit such as .


Diesel fuel "bugs" can cause fuel filters to block., with subsequent engine malfunction, or worse still, engine stoppage.

Diesel fuel "bugs" are actually micro-organisms comprised of fungi, yeasts and bacteria which live mostly in the diesel / water interface inside the diesel tank. The common diesel ‘bug’ is the fungus Hormoconis resinae that can produce a large biomass of mycelia (fungal matting) in a short period of time if the conditions are favourable. Hormoconis resinae is called "diesel bug" in the diesel fuel industry and "jet fuel fungus" in the aviation industry. 

The mycelia of Hormoconis resinae excrete acids that can break down weaker tank material such as aluminium.

Water, nutrients and warmth are the pre-requisites for "bugs" to rapidly grow, blocking filters and damaging engine fuel components. Water can be either free water (fresh or salt) or emulsified water.  Free water may have come from faulty bulk storage tanks, or from rain or sea water entering through fuel tank filler caps with faulty seals. Nutrients can include the alkanes in the fuel, dead "bugs" and even the fuel tank material.  Warmth is usually from the local ambient conditions, but diesel tanks in engine rooms and non-cooled high flow return lines into small fuel tanks will increase the diesel tank temperature.

Long storage of diesel fuel also increases the potential of "bugs" to grow.


Diesel “bugs” should not be confused with asphaltene chemical sludge compounds formed as diesel fuel ages.  Asphaltene sludge can also cause fuel filters to block with subsequent engine malfunction, or worse still, engine stoppage.

Diesel fuel degrades with time (faster at higher ambient temperatures), often forming insoluble asphaltene compounds through an oxidation process. Prevention is the best cure.  Use fresh diesel fuel where possible, which may mean keeping fuel tanks partially full if they are not used frequently.  This can be a "Catch-22" situation, as condensation (water) is more of a problem in partly full tanks.  Condensation promotes "bug" growth and rust to form.


"Bug" (microorganism) growth can be prevented by good fuel management procedures and specific fuel additives.  Removing water that accumulates in your diesel tank is the best method of controlling "bug" growth.  Do this by draining any accumulated free water weekly.  Fitting an in-line see-through water catchment bowl makes draining water relatively easy.

There are some "bugs" in all diesel fuel, no matter how ‘clean’ it looks, therefore an additive such as FTC, or a specific biocide and a magnetic unit such as the ‘Bug Disrupter’ will be worthwhile ‘tools’ in your fuel management regime.

Other news and updates from Rosmac


Articles - Rosmac Ltd

ARTICLES on all sorts go in here, many of which have links to useful products. How to simply check engine oil condition and extend oil life. Problems that may easily be solved with a simple-fix. For machines and engines from the experts.