A. Fuel is stored in tanks or transported in tanks which can have contaminants in the form of rust. Also, dust can be introduced during the filling process. In addition, all fuels are not equally clean. Sometimes you will end up with poorly filtered fuel even after refining. The smallest contaminant can clog a fuel injector or damage the pintle valve and set. What it boils down to is that the fuel filter prevents costly problems from developing in your fuel system. It is no wonder the car manufacturers recommend fuel filter replacement every 30,000 miles or less.