General Information

Contamination Testing

Fungi and other microorganisms can survive and multiply in diesel fuel if water is present. The fungi can be present in any part of the fuel handling system. These fungi grow into long strings and will form into large globules. The growths appear slimy and are usually black, green, or brown. The fungi may grow anywhere in the fuel but are most plentiful where diesel fuel and water meet. As the fuel is agitated, when service station tanks are being filled, fungi are distributed throughout the tank and may be pumped into a vehicle.

Fungi use the fuel as their main energy supply and need only trace amounts of water and minerals. As they grow and multiply, they change fuel into water, sludge, acids, and products of metabolism. The most common symptom of contamination is fuel filter plugging; however, corrosion of metal components such as the fuel tank, pipes, and the injection pump may also be present.

Caution: Avoid physical contact with the biocides in order to avoid personal injury.

This procedure checks for the presence of water and gasoline in the diesel fuel that can damage the injection pump and the nozzle:

1. Remove the fuel filter element.
2. Inspect the fuel filter element.
- If water, gasoline or fungi/bacteria are not present, end the inspection.
- If water or fungi/bacteria are present, refer to Fuel Manager/Filter Water Draining.
- If gasoline is present, refer to Cleaning Gasoline from the Fuel System.