Spark Plug Overheating
Overheating is indicated by a white or gray center electrode insulator that also appears blistered (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.
CAUTION:
If the engine is equipped with copper core ground electrode, or platinum tipped spark plugs, they must be replaced with the same type/number spark plug as the original. If another spark plug is substituted, pre-ignition will result.