The Filter Head Gasket is a component found in diesel engines that filters the fuel before it enters the engine. It is situated between the filter housing and the engine block, ensuring a tight seal to prevent fuel leakage. The gasket acts as a barrier against any impurities or contaminants present in the fuel, stopping them from entering into the engine's combustion chamber. Over time, Filter Head Gaskets may wear out or become damaged due to constant exposure to heat and pressure, leading to leaks and decreased engine performance. Replacement of this gasket should be carried out as per manufacturer's specifications to avoid any potential damage or malfunctioning of other parts of your truck’s fuel system.