Hello. I changed my spark plugs at roughly 55k. While I was getting my oil changed i asked my local mechanic about the interval change. Well what he told me that most new car a days have iridium plugs and that they are good up to 100k. He told me that i changed my plugs way too early. He also did say that the copper ones you would need to change every 30k but not the iridium. My car is coming up on 30k since I last changed them. So who do I believe? You guys say to replace every 30k. Or are my plugs good till 100k?