Fuel Contamination

Diesel Exhaust Fluid (DEF) 

Diesel Exhaust Fluid (DEF) is a corrosive fluid that also tends to form deposits on components. If diesel fuel becomes contaminated with DEF, any part of the fuel system that has come into contact with the contaminated fuel must be replaced. Do not attempt cleaning a DEF contaminated fuel system because damage to components has already occurred.

Fungi and Micro-Organisms 

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. Service station tanks may contain fungi that could be pumped into a vehicle during refueling.

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 is fuel filter plugging, however various metal fuel system components including fuel sender assembly, pipes, fuel injectors, and fuel injection pump can corrode.

If fungi have caused fuel system contamination, use a diesel fuel biocide to sterilize the fuel system. Do not exceed the dosage recommended on the label. Discontinue the use of a biocide when towing a trailer due to possible engine power loss. It is permissible to have biocide in the fuel when starting to tow, but do not add any biocide while towing.

Gasoline 

Gasoline contamination will cause driveability concerns and a possible hard starting or a no start condition if the overall content is large enough. Gasoline raises the API rating and reduces cooling and lubrication, resulting in possible component failure.

Water 

Water or other like contaminates in fuel will also create driveability concerns and loss of engine power. If water is present in the fuel system, the fuel cannot cool and lubricate the components, causing overheating, rust and corrosion. This can result in component failure. Water can enter the fuel system in several ways, either through a contaminated refueling source, or through long term condensation the vehicle fuel tanks.