What does the engine do?
The engine is the heart of the vehicle, converting the energy stored in fuel into the power required to move the vehicle and run accessories such as heating, air conditioning and lights. Filters for oil, fuel, and the air required for combustion must be replaced periodically in order to prolong engine life and maximize efficiency.
The heat and friction generated by the engine causes service items to eventually wear. Engine oil contains additives that protect the engine from wear and corrosion, and these additives become depleted over time. Spark plugs ignite the fuel and air mixture in a gasoline engine; the constant electrical arcing eventually causes the plugs to wear out.
Accessory drive belts and timing belts constantly flex and become worn over time.