A fuel filter can actually filter too much. You can filter so many particles out of your fuel that the filter clogs almost immediately. If the filter allows too many particles to pass into your fuel delivery system you end up with clogged jets and injector nozzles. You need to find that special spot between too much and too little.
Boeing found that a large number of fuel contamination problems can be traced back to the actual fueling process itself. This is probably the case with cars as well. In other words you can start with clean fuel but once you start putting this fuel into your car you introduce a significant amount of particulates. Anytime you transfer fuel from one container to another you introduce contamination.
One source of contaminants that you may not have considered is the fuel tank vent line. As the fuel tank is drawn down ambient air is drawn into the tank through this vent line. Remember we’re talking about particles that are only three or four microns in diameter.
Microns: Everyone talks about the size of the particles their fuel filter can capture. They describe these particles in terms of a micron. A human hair can be anywhere from 30 to 600 microns.
Some racers have tried putting 3-micron paper filters on their EFI systems, only to see the filter clog up quickly. A number of people feel that 20-micron is best for most fuel systems.
Wix racing filters have a micron rating of 7 but these filters can only operate below 50 psi. Wix also makes a cartridge filter for the larger Fram fuel filters. These have a 5.9-micron rating and can operate up to 150 psi. K&N fuel filters start at 25 microns and go up to 100 microns depending on the filter model.
The injector manufacturers for EFI systems would all like fuel come to their injectors with no particulate larger than 3-microns. They also know that if a racer puts on that type of filter it will clog quickly so they all recommend a 10-micron element.
Ten years ago Kinsler developed a two-layer fuel filter element. It has an inner layer of 3-micron precision grade filter Fiberglass, with an outer layer of 10-micron paper. The paper takes out about 90% of the dirt, so it protects the 3-micron layer from clogging too quickly. This is an effective solution to the problem.
Dirt Holding Capacity: The basic idea is that the fuel filter will trap particles and then hold them in place. We have to consider which type of filter has the best holding capacity: Paper or a screen? I’m not even going to discuss the old bronze filters since they can’t hold much dirt at all. Paper holds more dirt per square inch than a metallic media because paper is a depth media. That is, the dirt can work its way down into the paper element through a lot of little holes. The problem with paper is that unless you use a premium paper (which very few manufacturers do) paper particles come off the “clean” side of the element and migrate into your fuel system.
The metallic screen type of element won’t shed any pieces but they only catch dirt on the surface. They can’t capture and hold the particles. Metallic filters only have about one-third the dirt holding capacity of paper.
Location: Kinsler feels that whether you’re running an electric or mechanical fuel pump it should be protected by a filter on the inlet side. They feel the screen is necessary because unless you run a huge paper element the filter will be too restrictive. The inlet side of the pump is extremely sensitive to cavitation. If you pull the slightest pressure on the incoming side warm fuel can cause the pump to cavitate and seriously reduce the fuel pump outlet flow.
Size: You should always run the largest filter you can fit into your car. No matter how large your fuel filter might be though you still need to develop a regular schedule for replacement.
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| The Kinsler dual-element filter |
Ethanol: If you use gasoline that contains ethanol you simply can’t change your filter often enough. Ethanol acts as a cleaner in your fuel system. Residue from your fuel tank and fuel lines ends up in your fuel filter. The Donaldson Company, which specializes in industrial filtration, found that more than 95% of all premature filter failures are a result of chemical changes in fuel composition, not from good old- fashioned dirt as in the past.
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