A few years ago I read a Denso paper (still have it if anyone is interested) describing Denso's effort to develop an iridium plug which would last 200k miles BEFORE dropping off in performance. They presented all of the test results which showed they had accomplished their objective. I have changed out a few sets of iridium plugs at 120-150k miles and they all looked as good as new. Last night I changed out the NGK iridiums in my niece's 2007 TSX with 130k miles. I looked at them under magnification and the electrodes looked just like the new ones. It was amazing. I changed them out but I have no doubt they could have easily gone 175-200k miles.
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