Spark Plugs: What They Do, When to Replace Them, and How to Choose the Right Ones

When your engine won’t start or runs rough, the problem might not be the battery or fuel pump—it could be something small but critical: a spark plug, a tiny component that creates the electric spark to ignite fuel in your engine’s cylinders. Also known as ignition plug, it’s the heartbeat of your combustion engine. Without it, your car doesn’t just lose power—it stops dead. Even though spark plugs are small, they handle extreme heat, pressure, and electrical voltage every time you turn the key. And when they fail, you feel it: misfires, poor fuel economy, or that annoying hesitation when you press the gas.

Not all spark plugs are the same. There are copper, the most common and affordable type, good for everyday driving but shorter-lived, platinum, a step up in durability, often used in modern cars with longer service intervals, and iridium, the premium choice with superior conductivity and lifespan, ideal for high-performance or turbocharged engines. Your car’s manual will tell you which one it needs—using the wrong type can cause overheating, misfires, or even damage to the cylinder head. And while some drivers think "more expensive means better," that’s not always true. A high-end iridium plug in a basic economy car won’t give you extra power—it’ll just cost more.

How long do they last? Copper plugs might need replacing every 20,000 to 30,000 miles. Platinum can go 60,000. Iridium? Up to 100,000 miles. But mileage isn’t the only factor. If you drive short trips often, your engine never fully warms up—this causes carbon buildup that fouls plugs faster. If you hear a rhythmic tapping or your check engine light flashes, that’s a red flag. So is rough idling or trouble starting on cold mornings. These aren’t just annoyances—they’re early signs your spark plugs are dying.

You don’t need a mechanic to check them. A simple visual inspection—pulling one out with the right socket—can tell you if they’re fouled, worn, or cracked. And replacing them yourself? It’s easier than changing your air filter. You just need the right tool, a little patience, and the correct gap setting. Skip the expensive shop fees. Do it right, and you’ll get smoother starts, better fuel mileage, and fewer surprises on the road.

Below, you’ll find real-world guides on how to test, replace, and choose spark plugs that actually match your car—not just what the auto parts store pushes. Whether you’re dealing with a worn-out set, confused by the options, or just trying to avoid a breakdown, these posts give you the facts without the fluff.