Spark Plugs: What They Do, How Long They Last, and When to Replace Them

When your engine fires up, it’s the spark plug, a small but critical component that creates the electric spark to ignite fuel in the combustion chamber. Also known as an ignition plug, it’s the heartbeat of gasoline engines—no spark, no start, no drive. You won’t see it unless you pop the hood and dig past the ignition coils, but if it fails, your car won’t move. And unlike brake pads or oil filters, most people don’t think about spark plugs until the engine starts misfiring, sputtering, or refusing to turn over.

Spark plugs don’t last forever. Most last between 30,000 and 100,000 miles, depending on the type. Standard copper plugs wear out faster—often around 30,000 miles—while platinum and iridium ones can go twice as long. But mileage isn’t the only factor. Aggressive driving, poor fuel quality, or a dirty air filter can make them wear out sooner. And if you ignore a failing spark plug, you don’t just lose power—you risk damaging your catalytic converter, wasting fuel, or even triggering a check engine light that leads to expensive diagnostics.

It’s not just about the plug itself. The ignition system, the full chain of components that delivers voltage to the spark plug includes coils, wires, and sensors. A bad coil can mimic a bad spark plug. A cracked plug boot can cause misfires. That’s why some posts in this collection focus on symptoms like rough idling, poor acceleration, or hard starts—not just to tell you when to replace the plug, but to help you spot what’s really wrong.

And it’s not just about old cars. Even modern engines with advanced fuel injection and computer controls still rely on spark plugs. Electric vehicles don’t need them, but if you drive a petrol or hybrid car in India—whether it’s a Maruti Alto or a Toyota Fortuner—you’re running on spark plugs. And with fuel prices fluctuating, keeping them in good shape means better mileage and fewer surprises on the road.

Some people think spark plugs are a "set it and forget it" part. They’re not. They’re like tires: you don’t wait until they’re completely gone to check them. You look for signs. A black, oily tip? That’s oil burning. A white, chalky tip? That’s overheating. A gap that’s widened too much? That’s wear. You don’t need a garage to spot these clues. A quick visual check with a plug socket and a flashlight can save you from a tow truck.

This collection brings together real-world advice on spark plug lifespan, signs of failure, replacement costs, and how to avoid being upsold on unnecessary upgrades. You’ll find posts that break down the differences between iridium and copper plugs, explain why some engines need special plugs, and show you how to tell if your misfire is the plug—or something else entirely. We also cover related issues like ignition coils and fuel efficiency, because spark plugs don’t work in isolation. They’re part of a system. And when one part fails, it drags the rest down with it.

Whether you’re trying to fix a rough idle, save money on fuel, or just understand why your car won’t start on a cold morning, the answers are here. No fluff. No theory. Just what works, what doesn’t, and what you need to know before you open your hood.