How Long Do Spark Plugs Last? Signs, Lifespan, and When to Replace

When your car sputters, stalls, or refuses to start, the culprit might be something small but critical: spark plugs, small but essential components that ignite the fuel-air mixture in your engine’s cylinders. Also known as ignition plugs, they’re the reason your engine turns over and runs smoothly. Most modern spark plugs last between 30,000 and 100,000 miles, but that number isn’t set in stone. If you drive mostly short trips, in stop-and-go traffic, or with a dirty air filter, they wear out faster. On the flip side, if you use high-quality iridium or platinum plugs and drive mostly on highways, they can easily hit 100,000 miles without a problem.

But here’s the thing: you shouldn’t wait until your car won’t start to check them. engine misfire, when one or more cylinders fail to ignite properly is the first real warning. That’s when you feel the engine shake, hear a rough idle, or notice your car hesitating when you press the gas. poor fuel economy, a sudden drop in miles per gallon without any other changes is another red flag. If you’re filling up more often and your driving habits haven’t changed, your spark plugs could be the reason. And don’t ignore the check engine light, a simple indicator that your car’s computer detected a problem—it often points to spark plug issues before you even feel them.

It’s not just about mileage. Spark plugs get coated in oil, carbon, or fuel deposits over time, especially if your engine burns oil or runs rich. That’s why a 5-year-old car with only 40,000 miles might need new plugs, while a 10-year-old car with 120,000 miles might still be running fine on the originals. The real question isn’t just how many miles you’ve driven—it’s whether your engine is performing like it should. If you’re struggling to start the car on cold mornings, or your acceleration feels sluggish, those are signs your spark plugs are tired.

Replacing them isn’t hard, and it’s one of the most cost-effective upgrades you can make. A set of spark plugs costs less than a tank of gas, and doing it yourself takes under an hour with basic tools. But skipping it? That’s when you risk damaging your catalytic converter, wasting fuel, or getting stuck on the side of the road. The posts below break down exactly what to look for, how to test your plugs, which types last longest, and how to avoid common mistakes when replacing them. You’ll find real-world stories from people who waited too long—and what happened when they finally acted.