depends on the vehicle but i recommend every 30,000 mi. otherwise you will end up ruining a head trying to remove the old plug with carbon buildup and all
According to the owners manual, they have platinum plugs that should be changed at 100,000 miles.
If they are platinum plugs, should be every 95,000 to 100,000 miles.
A standard spark plug should last about 50K. A platinum tip plug should last 100K.
platinum plugs 75,000 miles. resistor plugs 30,000.
regular copper plugs (suppressor or resistor) 30k miles single platinum plugs with DIS type I or type II ignition 45k miles single platinum with distributor (presumably HEI) or COP ignition 60k miles double platinum plugs 60k miles iridium plugs 100k to 120k miles, possibly longer This assumes that you do not have a known or suspected problem with any of your spark plugs
Generally I change platinum plugs at 100K and regular plugs at 50K.
100K if they are platinum plugs, 50K if they are regular plugs.
Every 30,000 miles except platinum plugs
Standard spark plugs, 50000 miles. Platinum tip spark plugs, 100000 miles.
If you have platinum spark plugs, 100K. If you have standard plugs, 50K.
It seems to depend on the spark plug. I replaced the Motorcraft plugs with Bosch Platinum+2 plugs. Look here for what Bosch says about torques (search for the word "torque"): http://www.boschautoparts.com/Resources/FAQS/SparkPlugs.htm The box of the Platinum+2 plugs said to torque them to 15 ft.-lbs., which is what I did. Good luck!
factory recomends every 30,000 miles or 60,000 if you are running platinum plugs.