The selection of a spark plug of the proper heat range for automotive service is becoming increasingly difficult in spite of the many improvements in design and materials that the spark plug manufacturers have made available. In automotive engines the combination of high-power potential with low-power demand in congested urban driving makes it difficult to provide a spark plug which minimizes electrode erosion and preignition problems, and gives maximum resistance to fouling. Present production spark plugs give satisfactory performance under most operating conditions, although difficulty may be experienced in light-load service.
Various types of spark plug failures and the mechanisms of plug fouling are described. Some data are presented which relate to the effect of operating conditions, spark-plug heat range, spark-plug design and ignition-system characteristics on fouling of spark plugs in passenger-car service. Possible solutions are indicated such as careful selection of the plug heat range and design for various services, and the use of 12-volt or high-frequency ignition systems.