Notice: The recommended change interval for the platinum tip spark plugs is 100000 miles. If a spark plug is removed from the engine and there is no malfunction associated with the plug, reinstall the old plug in the engine.

Tapered seat spark plugs without gaskets are used on these engines. Both use a resistor type, platinum tip spark plug with a 0.060 inch gap. Refer to Maintenance and Lubrication for spark plug type. Always replace plugs with the same spark plug as listed.

Normal service is assumed to be a mixture of idling, slow speed, and highway driving. Highway driving is needed for good spark plug performance because it gives increased combustion heat that burns away any excess deposits of carbon or oxides that have built up from frequent idling or continual stop-and-go driving. Spark plugs are protected by an insulating boot made of special heat-resistant material which covers the spark plug terminal and extends downward over a portion of the plug insulator. These boots prevent flash-over which causes engine mis-firing. Do not mistake corona discharge for flash-over or a shorted insulator. Corona is a steady blue light appearing around the insulator, just above the shell crimp. It is visible evidence of a high-tension field, and has no effect on ignition performance. Usually it can be detected only in darkness. This discharge may repel dust particles, leaving a clear ring on the insulator just above the shell. This ring is sometimes mistakenly regarded as evidence that combustion gases have blown out between the shell and the insulator.

Spark plugs must operate within certain temperature limits if they are to provide the performance and service expected. The spark plug selected for an engine is based on the normal service for which the engine was designed.