Cherokee 4WD L6-4.0L VIN S (1998)
Spark Plug Overheating
Overheating is indicated by a white or gray center electrode insulator that also appears blistered. The increase in electrode gap will be considerably
in excess of 0.001 inch per 1000 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.