All gasoline internal combustion engines operate by burning a mixture of compressed gasoline and air. They all use a spark plug to start the burning process. The spark plugs work by a split second charge of high voltage electricity passing across a gap at the electrode. The voltage can be as much as 40,000 volts. They must perform this task every time each cylinder fires. This relates to about 90,000 times every mile. They must perform their task in some very harsh environments. The inside of a cylinder can get to about 1700 degrees. The electrode slowly erodes away each time it fires. As it erodes the electricity cannot pass across the electrode gap as effectively. This causes the combustion to be less efficient. This happens so slowly you usually do not even notice the slight hesitation or loss of fuel economy. Older vehicles came equipped with a conventional metal for the electrode (tip) The erosion process is a good bit faster on that type spark plug. Some modern vehicles use a double platinum tip spark plug that holds up to the erosion about 3 times longer than a conventional one. For this reason we recommend the spark plugs be replaced regularly. A conventional spark plug needs to be replaced about every 30,000 miles and a platinum tip, between 60,000 and 90,000 miles.