[litespeedp]

Same puzzle here.Bought my 2000 2 yrs ago with 60,000 miles and no spark plug change history available so I had my indy change them at 70,000 miles last week.

Plugs should not be affected by time as the hydraulic fluids etc IMO.

I have heard that the relatively short Porsche suggested interval is based on the fact that they could be difficult to remove without causing some stripping in the softer aluminum head if they remained in place a long time.

Modern ignitions are so clean and powerful that my plugs looked great when I examined them.

I only put about 5,000 a year on mine.I'm not afraid of the time element, so it will be very many years before my next change!