flyhigh@mach1

Well that's good news! 100,000 miles is the recommended change interval, isn't it? Any reason to change it earlier if all seems to be running well?

Torch_Vert

It's up to you, but I see a difference in plug performance after swapping fresh ones in at 10K-15K, I tend to think they'd be rather seriously degraded by 100K.

Also, there's the chance that the steel plugs in aluminum heads are possibly going to seize due to galvanic action between the dissimilar metals. Six plugs at a couple bucks apiece now and then just seems like really cheap insurance to me.

xjonshecklerx

Will Ford replace the head on a warranty vehicle if it was the owner that fouled the threads? My friend cross threaded his spark plug but was able to get the factory plug back in straight.

Torch_Vert

Not if they know you friend did it. That falls under "abuse".

JimC

How is it a warranty issue when your friend is the one who did the damage? Ford warranties the work and product that they sold to you - what you do to it afterwards isn't the fault of their build.