Used Fuel Filter Analysis

September 2013

If your diesel fuel filter seems to plug faster than normal, it may be a good indication that you have a problem with contamination of the fuel itself. There are a number of different types of contaminants that can be found in diesel fuel today. Inspection of a used fuel filter can help you identify the type of fuel contamination you may have. Remember, if the fuel filter becomes plugged, it's more than likely doing its job…protecting your fuel system from harmful contaminants.

The following are some common identifiers of diesel fuel contaminants that can be found by inspecting a used fuel filter:

Figure 1    Media Covered with Slime (see Figure 1) – indicates a fungus or bacteria problem in
       the fuel. Treating the fuel system with a biocide should help to eliminate these

Figure 1    Oily, Black Substance on Media (see Figure 2) – indicates the presence of particulates
       (sometimes called asphaltines) in the fuel. These contaminants tend to settle in the
       bottom of fuel storage or delivery tanks, then get stirred back into the fuel during delivery.

Figure 1    Wavy Pleats of Media – indicates the presence of water in the fuel. This is the most
       common form of contamination in fuel. In cold weather, the water in the fuel may freeze
       and reduce or completely stop flow of fuel to the engine.

Figure 1    Gelation of Fuel (see Figure 4) – indicates that low temperatures have caused the wax
       within the fuel to gel. This gel will plug the fuel filter(s) as well as the fuel lines. Use of
       No. 1 diesel fuel, certain fuel additives or various types of fuel heaters may be used in
       cold weather environments in an effort to prevent waxing or gelation of the fuel.