Your engine's spark plugs are absolutely vital to the longevity and clean running of your engine. That's why they need to be changed regularly, and properly. Here's how to do that without making a mess of things.
Simply put, spark plugs ignite the fuel and air mixture in the cylinder by having electrons arc a gap at the end of the plug, known as the electrode. The resulting explosion creates pressure that is translated into crankshaft motion, and that is translated into motion via the drivetrain. Without spark plugs, a gasoline engine simply wouldn't go anywhere, so it's an absolutely vital component to the running of your car's engine.
However, If your car runs on diesel fuel, your engine doesn't have spark plugs at all, and simply relies on compression for combustion.
Over time, heat, carbon buildup, oil, fuel, and regular use can deteriorate the electrode and make the necessary gap too wide, resulting in inconsistent combustion and a less efficient fuel burn. If your car's idle stumbles, or you have hesitation on heavy acceleration, you may want to check your spark plugs. Usually, a spark plug may last anywhere between 30,000 and 60,000 miles. Here's an example of a badly worn spark plug, as seen on my Mitsubishi Eclipse GSX, which had both stumbling idle and hesitation when the turbo spooled up. notice the discoloration on the ceramic and metal:
Spark plugs come in may varieties, to suit your needs. If your car is stock, it's best to go with what the manufacturer recommends, as this will, more often than not, give you the most efficient burn possible. If your car isn't stock and you have forced induction power adders such as an aftermarket turbocharger or supercharger, it's good to go with one or two steps colder plugs, which does not mean that it has a lesser spark, just that it has a lower heat range in which it's most efficient. If you have a modified engine that's naturally aspirated (no turbo or supercharger), it's better to go with a hotter plug, as the efficient heat range shifts upwards.
While there may be a small difference in performance as far as electrode materials go, the big difference is longevity. As a rule of thumb, the more you pay for a quality spark plug, the longer you can expect it to last, the shortest being copper, and the longest being iridium. As spark plugs are relatively inexpensive, try to get the best ones your bank account can afford.
That's a simple question with no easy answer. Usually, if you have a spark plug with a central electrode made of copper or platinum, check the gap with a feeler gauge and make sure it conforms to the specific gap that is required by your car's engine. You can find this information by asking someone at the parts counter of your local auto supply store, or just by Googling. Spark plugs come pre-gapped, but with shipping and handling, sometimes the gaps can close, so it's best to check before installing. Note: Do not gap iridium plugs. Here's how to gap your plugs:
Now that you know what a spark plug does and what to look out for, here's how to change them. Please note that different cars have different methods of getting to the spark plugs with varying degrees of difficulty, so please make sure that you understand how to do this prior to going into this project head-first. Also, never work on a hot engine. The spark plugs are amongst the hottest parts of the engine, so it's imperative that you give the engine a few hours to cool down if it's been run up to temperature recently. Here's the procedure:
Tavarish is the founder of APiDA Online and writes about buying and selling cool cars on the internet. He owns the world's cheapest Mercedes S-Class, a graffiti-bombed Lexus, and he's the only Jalopnik author that has never driven a Miata. He also has a real name that he didn't feel was journalist-y enough so he used a pen name and this was the best he could do.