Detecting Deteriorated Gasoline

Moderate deterioration by any mode except contamination is impossible to detect without testing. However, testing by a qualified laboratory is impractical except when a large amount of gasoline or a very critical application is involved. While discarding deteriorated gasoline in an environmentally responsible way is not easy (see next section), it is the better answer for small quantities of questionable gasoline.

The modes of gasoline deterioration are:

Evaporation

The evaporation of some low-boiling components is impossible to detect without testing. Relevant tests are:

  • Test Method for Distillation of Petroleum Products; ASTM D 86 (American Society for Testing and Materials)
  • Test Method for Vapor Pressure of Petroleum Products (Mini Method); ASTM D 5191

If the first 10 volume percent of a gasoline distills above 160°F (summer) or 140°F (winter), the fuel no longer meets the ASTM specification for gasoline (Automotive Spark-Ignition Engine Fuel; ASTM D 4814).

A gasoline with a vapor pressure less than 5 psi (summer) or 9 psi (winter) is suspect.

Oxidation

Severely oxidized gasoline has a rancid odor and darker color. The presence of solid gum particles also may result in the loss of brightness and clarity. Testing is required to detect moderate oxidation:

  • Test Method for Existent Gum in Fuels by Jet Evaporation; ASTM D 381

Gasoline with a "washed gum" greater than 10 mg/ 100 mL is suspect.

Microbial Activity

Microbial activity tends to concentrate at the gasoline-water interface. Moderate activity may cause the gasoline to lose brightness and clarity. Severe activity may stabilize gasoline-water emulsions and contaminate the fuel with visible particles of microbial sludge (biomass). Anaerobic microbial activity may generate hydrogen sulfide, giving the gasoline a "rotten egg" odor.

Contamination

The common contaminants are dirt, water, and rust (generated when gasoline and water are stored in a steel container). All of these contaminants can be detected visually. However, since they all tend to settle, a sample from the bottom of the container or fuel tank is required.

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