I wanted Motorcraft platinum plugs but when I went to Autozone and they did not have them. They convinced me to try Autolite Iridium. I have not put them in but my fuel economy is down a bit and the car is running a bit rough when under throttle like passing someone. The car has nearly 140,000 miles now and I bought the car at 82,000 and have no idea if plugs have ever been changed.