The plugs are rated to last 'till 100K, but I can't see any spark plug maintaining peak effiency to 100,000 miles. I do mine every 30K, just 'cause I don't want any hassles of them getting stuck and breaking off.

 

Darn! I thought the 179,000 I had on the original plugs in my 94 T-100 was pretty good. I sold it to a cousin who probably still has the original plugs in it at 225,000.

The performance and efficiency didn't change from the day it was new until I sold it at 179,000 miles. The efficience hasn't changed on my 98 Towncar with 106,000 or 01 Escape with 98,000.

 

What is your location, warm weather? I live in NE OHIO were we get snow, because the Tech at my dealer mentioned trucks that plow are more likely to have the broken plug issue. I do not plow and took mine in for plug replacement at 53k mi. And the Ford technician broke 3 of 8 trying to remove them. I wanted them out just because of the seizure issue and got burned. But I did notice a difference in my engine's performance after replacing them. Please list your location when you speak of removing the plugs without problems. There is some commonality we need to find, location, factory assembled at, etc... You're lucky, I wasn't!