Spark Plug Lifespan: How Long Do They Last and What Happens When They Fail?

When your car sputters, loses power, or won’t start without a jump, the culprit isn’t always the battery. More often, it’s the spark plug, a small but critical component that ignites the fuel-air mixture in your engine’s cylinders. Also known as ignition plug, it’s the spark that makes your engine run—no spark, no drive. Most modern spark plugs last between 30,000 and 100,000 miles, depending on the type. Standard copper ones wear out faster, around 30,000 to 40,000 miles, while platinum or iridium plugs can go over 80,000 miles without trouble. But mileage isn’t the only clock ticking—time matters too. Even if you drive little, spark plugs degrade from heat, carbon buildup, and corrosion.

When spark plugs start to fail, your engine doesn’t just slow down—it starts to break down. A weak or dirty plug causes a misfire, when one or more cylinders fail to ignite properly. That means unburned fuel leaks into the exhaust, hurting your fuel economy, how efficiently your car turns gasoline into motion. You’ll notice it in the form of rough idling, hesitation when accelerating, or a check engine light that flashes. And if you keep driving, that misfire can overheat your catalytic converter—a far more expensive fix than replacing a few plugs. The problem isn’t just performance; it’s cost. A single misfiring plug can drop your miles per gallon by 10% or more. Over a year, that adds up to hundreds in wasted fuel.

It’s not just about mileage or symptoms—it’s about timing. Many drivers wait until something breaks before they act. But spark plugs don’t fail suddenly. They fade. You’ll feel it in the way your car accelerates, hears it in the idle, and see it in your fuel receipts. Replacing them before they cause damage is cheaper, safer, and smarter. The good news? It’s a simple job for most cars. You don’t need fancy tools or a garage. A socket, a torque wrench, and a little patience are all you need. And if you’re not sure what kind your car uses, checking your owner’s manual or asking a mechanic takes two minutes. Don’t wait for your engine to warn you. By the time it does, the damage might already be done.

Below, you’ll find real-world guides from drivers and mechanics who’ve dealt with worn plugs, misfires, and the quiet decline of engine performance. From how to spot the early signs to what happens when you skip replacement, these posts give you the facts—not guesses—so you know exactly when to act.