What is the stuff clogging my fuel filters?

December 5th, 2009

Filter plugging can have several causes. For example, low temperatures can cause wax crystallization, which can lead to filter plugging. An example would be using summer diesel in cold weather. Wax or paraffin is part of the diesel fuel. A proper preventative additive with an Anti Gel agent is the answer to that problem.

Chemical incompatibility may cause dramatic filter plugging. This may happen when fuels with incompatible additive packages are mixed.

Clogged Diesel Fuel Filters

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Contaminant build up resulting from excessive microbial growth and bio-degradation of fuel can cause filter plugging. Micro-organisms, bacteria and enzyme activity, fungus, yeast and mold cause fuel degradation and the formation of waste products. The process is similar to milk turning into cottage cheese, a different form of milk. Of all the microbial debris and waste products in the tank only about .01% is bugs. Even though microbes may cause and accelerate the process of fuel degradation, it should be clear that the waste products clogging your filter are not the microbes but fuel components which have formed solids.

Frequently, the application of a biocide aggravates the situation and turns bio-film into solids, creating a real fuel filter nightmare. Bio film develops through out the entire fuel system. It grows in the water fuel interface and on the walls, baffles, and bottoms of storage tanks. An unlucky end user may be filling up his tank and getting this debris delivered as a part of his fuel, for the same price as the fuel.

Poor thermal fuel stability can plug filters. Fuel will form particulates (solids) when exposed to pumps and the hot surfaces and pressure of the fuel injection system. This will result in an increase in asphaltene agglomerations, polymerization and a dramatic loss of combustion efficiency.

Fuel systems, in general, are designed to return a significant proportion of the fuel, not used for combustion, back to the tank. This return fuel is very hot and will promote polymerization and fuel breakdown. Eventually, more and more solids from the tank will reach the filter and over time, plug the filter. These problems continuously occur in commercially operated engines, such as trucks, heavy equipment, shipping, and power generation, but will also appear in recreational boats, RV’s and all types of fuel storage tanks.

Truck engines are used continuously and, in most cases, the tanks “appear to be clean”. However, a 2-micron filter element does not last very long, in general 15,000 miles or less. It should be 30,000 miles or more. In the marine industry 400 hours is in many instances SOP while filters should easily last 1000 hours or more.

The size of the largest diesel fuel molecule still within specs is approx. 30 Angstrom (that equals approx 0,003 of a micron). Compared to a 10-micron opening in a filter element, one can have 3333 of these particular molecules passing through the opening side by side. E.g. comparing the size of a baseball to two and a half football fields.

Short filter life is quite remarkable realizing how “thin” diesel fuel actually is and knowing how clean the tanks on most trucks “appear” to be.

Short filter life is symptomatic of polymerization, increase in the size of the fuel droplet, agglomeration of asphaltenes and the formation solids in fuel systems. The consequences are carbon build up in engines and exhaust systems, higher fuel consumption and excessive smoke.

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