My 98 5.4 liter has 72000 miles and runs nicely but the book says i should get new plugs after 60k miles. Is it really necessary if it is running well? I know many platnium plugs on other vehicles are rated for 100k miles, so i don't know why it is specified on my vehicle for 60k.

Just curious. It's not a big deal (actually, it's a big job or big expense).

 

Special metal plugs have little to offer in reality, despite mfgr's claims. If you do replace, stick with what Ford originally offered. Within the recommended mileage range, specialty metal plugs actually tend to resist spark, thus they last longer, but don't really produce better performance, and they cost more. Read the book written by Dr Jacobs re Jacob's Ignition Systems for more information on that.

 

http://www.fordtrucks.com/article/id...ter_F150s.html

Might find this article helpful.

As for what RR4E stated, while it is true that platiums don't produce the power (electrical spark) that copper plugs do in a literal sense, the difference is so small that it isn't even worth worrying about for the average Joe.

We're talking a total difference of maybe 1-2 hp on the very optimistic side. I for one would rather change my plugs 1/4 the times over coppers, especially on the 5.4L.

If you are going to change the plugs, make sure you use a double platinum plug, Motorcraft and Autolite make DP's and they can be had at any parts shack.