Microorganism Problems in Diesel Fuel
Ronald T. Schuler
Extension Agricultural Engineer

Bacteria and fungi can grow in diesel systems and cause engines problems such as clogged filters and injectors and corrosion. Water in the fuel is the key fuel contaminant allowing the growth of microorganisms in the fuel. Any steps to remove and minimize water contaminants will reduce the potential for these microorganism related problems.

These microorganisms may be aerobic or anaerobic and are able to grow in the water and use the diesel fuel as their food source. They produce a slime which can move through the fuel system and cause filters to become clogged and injectors to become fouled. Also these microorganisms produce acids which can corrode internal metal surfaces in the fuel system from the fuel tank to the injector. Many of the internal fuel system components such as fuel pump and injectors are manufactured with very close tolerances. Low levels of corrosion can lead to engine problems quickly.

Minimizing water contamination is the best solution. Sources of water in the fuel include water in the fuel as it is received on the farm and contamination after delivered to the farm. Insuring the filler caps for the on-farm storage, transfer tanks and engine fuel tanks are in-place will reduce direct water contamination. Water can contaminate the fuel through condensation from the air above the fuel in the tanks. To minimize this condensation, the fuel tanks should be kept filled as much as reasonable. One practice to consider when engines are in use on a daily basis is to fill the engine fuel tanks in the evening after operation instead of in the next morning before the day of work. Also if tractors or other engine powered equipment are going to be stored for long periods, fill the fuel tank before placing in storage.

Periodically removing the water from the fuel system will reduce the potential growth of the microorganisms. One tractor manufacturer recommends draining the water from the fuel tank and fuel filters every ten hours of operation. If the equipment is used daily, the water should be drained every day. Operator’s manuals should be checked for the manufacturer’s recommendation for fuel system maintenance practices.

One sign of problems caused by microorganisms is an accumulation of a slime material on the fuel filters. Fuel additives are available to destroy these microorganisms in the engine fuel system. Fuel suppliers will have information on the recommended additives. The engine fuel tank may need to be emptied and cleaned to more quickly remedy the problem. Special attention should be given to tractors and self-propelled equipment that has been stored for long time periods.

Minimizing water contamination of the diesel fuel will reduce the potential for problems due to microorganisms in the fuel. Using sound maintenance practices will reduce the problems associated with clogged fuel filters and fouled injectors. If signs of microorganisms are present, steps should be taken immediately to destroy and remove them from the fuel system.