Spark Plug Overheating

Overheating is indicated by a white or gray center electrode insulator that also appears blistered. See Fig 1. The increase in electrode gap will be considerably in excess of 0.001 inch per 2000 miles of operation. This suggests that a plug with a cooler heat range rating should be used. Over advanced ignition timing, detonation and cooling system malfunctions can also cause spark plug overheating.

Fig 1: Spark Plug Overheating

Courtesy of DAIMLERCHRYSLER CORP.