Spark Plugs -

The spark plug theory: It forces electricity to arc across a gap, just like lightning. The electricity must be at a very high voltage in order to travel across the gap and create a good spark. Voltage at the spark plug can be anywhere from 40,000 to 100,000 volts. The spark plug must have an insulated path for this high voltage to travel down to the electrode, where it can jump the gap and, from there, be conducted into the engine block and grounded. The plug also has to withstand the extreme heat and pressure inside the cylinder, and must be designed so that deposits from fuel additives do not build up on the plug. Spark plugs use a ceramic insert to isolate the high voltage at the electrode, ensuring that the spark happens at the tip of the electrode and not anywhere else on the plug; this insert does double-duty by helping to burn off deposits. Ceramic is a fairly poor heat conductor, so the material gets quite hot during operation. This heat helps to burn deposits from the electrode. How often do you need to change them ? If your car's engine is equipped with a carburetor, then you will need to replace the spark plugs about once a year or every 15,000 miles. For Fuel Injected engines before 1996 the plugs will need to be replaced every two years or every 30,000 miles. For Fuel Injected engines that are 1996 or newer, the spark plugs will only need to be replaced every 80,000 to 100,000 miles.