Spark plugs create a spark that causes the gasoline and air to explode in your cylinder, which creates power. Most cars have one spark plug per cylinder, so a V6 would have six spark plugs, an I4 would have four, etc. Some higher end engines like Chrysler's 5.7LV8 have two spark plugs per cylinder for a total of 16 plugs!
Most newer cars have platinum tipped plugs that are don't require replacement until 100,000 miles. Regardless, we recommend changing your spark plugs every 60,000 miles (or less, depending on your owners manual) because the plugs can get stuck if you leave them in for too long. Many newer cars have aluminum heads, which is a softer metal and if a plug gets stuck in an aluminum head, the head can be damaged when a stuck plug is removed.
The difficulty in changing your spark plugs varies greatly depending on what type of car you have. Most four cylinder cars are very easy to get at the spark plugs, whereas transversely mounted V6 engines can often require taking off the manifold and other components to get to half of the plugs. How do you know if you have a transversely mounted V6? Most front or all wheel drive cars with V6 engines are transversely mounted.
Another great reason to change your spark plugs on a regular basis is to increase engine performance. If your engine is misfiring due to faulty or worn spark plugs, your fuel economy will decrease by up to 25%.