My 1998 Expedition had the plugs at 100,000 miles. I bought it used at that time. It now has 160,000 miles. How often should the plugs be changed? This is my favorite car.

 

Such a big job on the 5.4 engine that it took Witt Ford in Sturgeon Bay, WI two days and two guys to R & R the plugs.

Ford put those Bosch Four Prong spark plugs in at about 130,000 miles. That was the first plug change. Cost was $400 for plugs and labor...I might hve been ripped.

I'd guess 150,000 'tween plug changes, or what ever the owner's manual says.

skip.

Here is the skinny on those plugs. From the dealer's installation.

The most platinum with four yttrium-enhanced ground electrodes and the most powerful spark.
If you require the best in platinum performance over the longest service life, Platinum+4 is the spark plug for you. Platinum+4's unique revolutionary firing technology combines the advantages of surface air gap technology, four yttrium-enhanced ground electrodes, and a heat-fused center electrode with the most platinum, creating the most powerful spark you can buy.

Were at 195,957 now.

 

Some people will drive the vehicle until it won't run anymore and then they can't understand why. Your owner's manual is the best answer. Not all people have the same driving habits so that is a consideration to keep in mind.