In the old days, a tune-up was necessary about every 35,000 miles. It would usually consist of setting the ignition timing, replacing the mechanical breaker points in the ignition, cleaning and adjusting the carburetor and replacing the plug wires and spark plugs. Today, of course, the carburetor’s job is done by fuel injection and the ignition timing and spark are controlled by the engine computer. Few vehicles still have plug wires anymore either, as the distributor was replaced by the computer and a coil-on-plug design which delivers a spark at each spark plug.
But what about the spark plugs themselves, though? How often do they need to be replaced now?
Manufacturers tout an 80k-100k mile service interval on spark plugs now, thanks in part to improvements in plug design and materials. That might be stretching it, however. Remember that if you have a 100,000-mile spark plug, its electrode is worn down 4/5 of the way at 80,000 miles. A worn ...[more]