Air Dryer

Fuel filters play an important role in today's modern, tolerant engine fuel system.  Unfiltered fuel can contain a variety of contaminants, such as paint chips and dirt that have been knocked into the tank during refueling, or rust caused by moisture in the steel tank.  If these substances are not removed before the fuel enters the system, they can cause rapid wear and failure of the fuel pump and injector due to the abrasive effect of the particles on the high-precision components used in modern injection systems.  Fuel filters also improve performance because fewer pollutants are present in the fuel and more efficiently it can be burned.  

The fuel filter needs regular maintenance.  This is usually a case of simply disconnecting the filter from the fuel line and replacing it with a new filter, although some specially designed filters can be cleaned and reused many times.  If the filter is not replaced regularly, it can become clogged with pollutants and limit fuel flow, leading to a significant decline in engine performance as the engine struggles to extract enough fuel to continue normal operation.  

Some filters, particularly those found on diesel engines, have bowl-shaped designs that collect water at the bottom (because water is denser than diesel).  The water can then be drained by opening the valve at the bottom of the filter and letting it run out until the filter contains only diesel.  Many diesel filters contain a water sensor that sends a signal to the engine control unit directly to the driver if the water level reaches a warning level.  In particular, it is not desirable to inhale water from fuel into the fuel system of a diesel engine, as this system relies on diesel to lubricate moving parts and if water enters moving parts that require continuous lubrication (such as the fuel injection valve), it can quickly cause overheating and unnecessary wear.  This type of filter may also include a sensor that will alert the operator when water from the fuel filter needs to be drained.  There may be a fuel heater near the diesel fuel filter to avoid paraffin formation inside the filter element (at low temperatures), which prevents fuel flow to the engine.