Platinum is a good conductor of heat and electricity, but it is best known for its ability to resist chemical corrosion and electrical erosion. That is why platinum is used on the electrodes of many spark plugs today. Some plugs have a solid platinum center electrode, while others have a small button of platinum welded onto the tip of center electrode or both electrodes (single platinum vs. double platinum). Platinum is used because it minimizes electrode wear. Every time a plug fires, a tiny amount of metal is vaporized and erodes from the surface of both electrodes. The center electrode typically suffers the most wear because it runs hotter than the side electrode. As the electrodes wear, the air gap across which the spark must jump becomes wider and wider. The gap on a standard spark plug grows about 0.00063 to 0.000126 inch for every 1,000 miles of normal driving. And the wider the gap, the greater the voltage needed to jump the gap. On standard plugs with conventional electrodes, the firing voltage requirements typically creep up about 500 volts for every 10,000 to 15,000 miles of driving. Eventually, the plugs may need more volts to fire than the coil(s) can produce, resulting in ignition misfire. On OBD II-equipped vehicles, too many misfires will cause the Check Engine light to come on.
