my truck has 90,0198 and as far as i know the spark plugs have never been changed, prolly about time though. ALSO i bought the truck almost 1 year ago this month and it had 56,000 miles on it, so i have put about 34,000 miles or so on it this year alone. 34,000 miles a year is a lot for a car or truck in my eyes.
my 2001 truck has 92,000 miles on it and the orig plugs and no problem. i took them out about 40,000 miles ago and they looked almsot new. but it is about time to replace them. what is it going to hurt if you do leave them in there. my gas has not dropped any and it doesn't ping any and the idle is smooth as a babies butt.
im changing mine today, weather they need it or not. they've got 83000 miles on them... so they're ready for a change. i too took mine out a while back, and they looked fine.. but that was like a year ago, so, this time im just going to change them weather they need it or not... can't hurt.
ford says they can go up to 100,000 miles before changing but my thinking is which i may be wrong is that since not only is my truck my dd but its my work vehicle and i tow a trailer everyday which probably weighs around if not more that 3000lbs fully loaded in constant stop and go traffic things are going to wear out faster so i replace them earlier than most people would have to. i had notice the idle was getting rough and fuel mileage was starting to go down so i decide to change then and what do you know gas mileage went back up and it idles a lot smoother. plus that 40 bucks spent now is money saved later.
2004 sonic blue ranger edge plus 4x2, 3.0, auto regular cab, stepside bed
Current mods: some
Future mods: to many to list
2005 dark gray metallic honda goldwing. makes up where the ranger lacks
I'd never leave plugs in a head for 100K.
Ruined a couple of heads by spinning the threads out of them from plugs that had rusted and siezed in, 40k is the absolute most.
The only reason they put plat plugs in is so they can get through the lease period and get sold before needing change, then the second owner "IF" he can get them out flips the bill, not Ford or the Dealer.
Cheap insurance to change at or before 40K
I beieve that most manufacturers list 100K miles for tune up and spark plug change to reduce the PUBLISHED cost of maintenance.
Modern plugs do last longer and my Ranger does not even have a cap or rotor, but keeping plugs in there for 100K does seem like pushing them.