Fungus and Bacteria -- live in water and feed on the hydrocarbons found in fuel.
Often called Humbugs for short, these active and multiplying colonies will spread
throughout a fuel system and quickly plug a fuel filter. The fuel filter will have a
slime-like coating over the surface of the media, dramatically reducing the
service life of the filter. Bacteria may be any color, but are usually black, green or
brown. Draining the system will reduce microbial activity, but will not eliminate it.
The only way to eliminate microbial growth once it has started is to clean and
treat the system with a biocide.
Wax -- is desirable as a source of energy in fuel, but control in cold weather
operation is needed. Wax crystals form as a result of cold temperature
precipitation of paraffin. Temperatures below a fuel's cloud point will result in wax
precipitation and filter plugging. To prevent plugged filters due to wax formation,
the cloud point of fuel must be at least +12° Celsius (+22°F) below the lowest
outside temperature. Fuel suppliers blend diesel fuel based on local anticipated
cold weather conditions. Particular attention should be given to diesel fuel
purchased outside your local area. For example, fuel purchased in the West or
South may not be suitable for operating conditions in the Midwest or North.
Asphaltenes -- are by-products of fuel as it oxidizes. Asphaltene particles are
generally thought to be in the 0.5 – 2.0 micron range and are harmless to the
injection system, as they are soft and deform-able. As these tiny particles pass
through the filter media they tend to stick to the individual fibers. If you were to
cut open a filter that had choked after a normal service interval you would see a
black, tarry substance on the dirty side of the element; this is asphaltene
(oxidized fuel). Fuel with a high percentage of asphaltenes will drastically shorten
the life of a fuel filter.
Sediment and other solids -- often get into fuel tanks and can cause problems.
Most sediment can be removed be these contaminants before they by settling or filtration. Fuel filters designed for
specific applications will cause fuel