Diesel Fuel Storage And Contaminants

What Can Really Harm Your Fuel

Under normal diesel fuel storage conditions, diesel can be expected to remain in useable condition for 12 months or longer at an ambient temperature of 68 degrees Fahrenheit. It lasts 6-12 months at an ambient temperature higher than 86 degrees Fahrenheit. As diesel ages, sediments and gum form in the fuel brought about by the reaction of diesel components reacting with oxygen. More specifically, gums can be formed from chemical changes to the fuel, notably by exposure to oxygen, high temperature, acids, and metals during storage. Gums drop out of the fuel in the form of sediment, which can block injectors and fuel filters. This can lead to fuel starvation and the engine stopping. In order to keep the engine going, periodic fuel polishing is required. The gums and sediments do not burn very well in the engine, and can lead to carbon and soot deposits on injectors and other combustion surfaces.

In addition to gums and sediments, aging, dirt, rust, and water can all cause diesel to deteriorate in quality. Aging can be accelerated by:

  • Contact with zinc, copper, or metal alloys containing either metal. These will react with diesel fuel to form unstable compounds.
  • Water. Water allows the growth of fungus and bacteria. These produce natural by-products such as organic acids which make the fuel unstable.
  • Extreme temperatures.
  • Exposure to dust and dirt which contain trace elements that can destabilize the fuel, such as copper and zinc.
  • Fuel composition. Some fuel components can age quickly.

Dirt, dust, sand, and similar contaminants commonly enter through fill pipes, access hatches, and breather pipes. The amount of contamination will be noticeably worse in dusty areas. Rust can occur as corrosion debris from storage tanks and distribution system parts. These contaminants can plug filters, and can also support fungal growth and encourage fuel degradation. If left untreated, fungal contamination will increase corrosion, producing more rust.

Water can enter the fuel system as part of the refining process, as rain, or as condensation. Un-dissolved water will form droplets which make the fuel appear hazy or milky. Water can enter fuel tanks in the air, and will condense when the ambient temperature drops below a certain point. Water in the fuel system will cause corrosion and promote fungal growth.

Various species of fungus, bacteria, and yeasts are able to grow in fuel, given the presence of water. Most of these organisms produce acids, which can corrode engine parts. Colonies of bacteria is prevalent where fuel is allowed to remain still, such as in generator tanks. Colonies of organisms can plug filters and screens in the fuel system. These bacterial colonies will appear as slimes and scums.

In addition to fuel contaminants, filter blockages can cause problems as well.