What is the stuff that clogs my filter?

Written by Capt. Jeff Werner
Written by Captain Jeff Werner

Filter clogging can have several causes. For example, low temperatures can cause wax crystallization, which can lead to filter clogging. An example would be using summer diesel in cold weather. Wax or paraffin is part of the diesel fuel.

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

Contaminant build up resulting from excessive microbial growth and bio-degradation of fuel can cause filter clogging. Microorganisms, 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.

Even though microbes may cause and accelerate the process of fuel degradation, it should be noted that the waste products clogging your filter are not the microbes, but fuel components which have formed solids.

Frequently, the application of biocides aggravates the situation and turns bio-film into solids creating a real fuel filter nightmare. Bio-film develops throughout 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 part of the fuel, for the same price as the fuel.

Poor thermal fuel stability can clog 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 portion of the fuel, not used for combustion, back to the tank. The 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 clog 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.

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

Capt. Jeff Werner, a Licensed USCG Master, has sailed professionally throughout the world.  He is also the Diesel Doctor, helping to keep your boat’s fuel clean and bright.

If you have additional questions for Capt. Jeff Werner, please email him [email protected].