I can understand mileage affecting plug degredation, but the time limit is not at all clear to me.
What affects the efficiency of a plug made up of metal alloys and ceramics over a 4 year period screwed into an alloy cylinder head, unless electrolytic action between the threads of the plug and cylinder head is a potential probem.
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2001 Boxster S (triple black). Sleeping easier with LN Engineering/Flat 6 IMS upgrade, low temp thermostat & underspeed pulley.
2001 MV Agusta F4.
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