Choosing a replacement plug
Choosing new spark plugs isn't as easy as it used to be—dozens of choices are available. Here's what you need to know:
Tip 1: It's best to stick with the types of plugs you rode in on. The car manufacturer may have originally installed plugs made with precious metals. Platinum, yttrium and iridium plugs are more expensive than traditional plugs, but the coatings provide much better wear resistance and maintain their gap longer. Never downgrade to a less expensive plug. Your savings will be quickly offset by the shorter service life and reduced gas mileage. Consult your owner's manual or ask the auto parts store for the manufacturer's recommended plug.
Tip 2: Some plugs have adjustable-plug gaps and others have a fixed gap, but gap is always important. If the store recommends a fixed-gap plug, check your owner's manual to make sure it's the correct gap. If it isn't, find another brand. If the gap is adjustable, make sure you check (and adjust if necessary) the gap on each plug before installation.
The auto parts store computer showed eight different plug choices for a 1999 Ford Taurus. Prices ranged from $1.79 for a traditional plug to $14.99 for iridium. We chose the $2.79 double platinum type because that's what had been installed at the factory.