The spark plug is an electrical gadget that fits into your cars cylinder head where it will spark, when you turn your key in the ignition, to ignite the fuel. The spark plug forces electricity to arc across a gap, just like a bolt of lightening. 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 passageway 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 off deposits from the electrode. Some cars require a hot plug. This type of plug is designed with a ceramic insert that has a smaller contact area with the metal part of the plug. This reduces the heat transfer from the ceramic, making it run hotter and thus burn away more deposits. Cold plugs are designed with more contact area, so they run cooler. The difference between a “hot” and a “cold” spark plug is in the shape of the ceramic tip. The engineer will select the right temperature plug for each car. Some cars with high-performance engines naturally generate more heat, so they need colder plugs. If the spark plug gets too hot, it could ignite the fuel before the spark fires, so it is important to stick with the right type of plug for your car. Here at AE Services in Sutton we recommend that the spark plugs are changed during a service which will usually be carried out once a year. Go to www.autoexpressservices.co.uk for more information.