Fuel filters trap contaminants present in fuel, diesel oil and even in LPG installations, protecting precise elements of I. C. engines fuel systems from rapid wear. These fuels contain contaminants from the production process and distribution. Dust, soot from outer tank surfaces, water and micorganisms may cause the rapid wear of injectors, pumps or pressure-regulating valves in modern engines. Therefore each fuel system has filters which are optimally selected according to engine requirements, fuel quality and expected exploitation conditions. Requirements for filters are very high. In modern engines it is required that contaminants the size of 3 ÷ 5 µm are stopped with the effectiveness of more than 90%. In many cases more than one filter is installed in the car fuel system for better performance. However, in comparison with oil filtration, there are no by-pass valves in fuel filtration which clear the fuel flow when the filters are clogged. That’s because there is a rule that only clean fuel goes into the combustion chamber. Therefore it is better that the engine stops due to lack of fuel (dirty filters) than if it had to work using non filtered fuel.