Can I Drive with Bad Spark Plugs? What Happens and When to Replace Them
Driving with bad spark plugs may seem harmless at first, but it can lead to expensive engine damage. Learn the signs, risks, and when to replace them to avoid costly repairs.
Driving with Faulty Spark Plugs: Signs, Risks, and What to Do
When your faulty spark plugs, small but critical engine components that ignite fuel in the combustion chamber. Also known as ignition plugs, they’re the reason your car starts and runs smoothly. If they fail, your engine doesn’t just sputter—it starts falling apart in ways you might not notice until it’s too late.
Bad spark plugs don’t just make your car hard to start. They cause engine misfire, a condition where fuel doesn’t burn properly in one or more cylinders, which leads to rough idling, hesitation when accelerating, and sudden power drops. This isn’t just annoying—it’s expensive. Unburned fuel flows into your exhaust system, the pathway that carries waste gases out of your engine, and coats your catalytic converter in gunk. That’s a $1,000+ repair waiting to happen. And yes, it can make your car fail its MOT because of high emissions.
You might not realize your spark plugs are bad until your fuel economy drops by 20% or you hear a rhythmic popping sound from the engine. Other signs? The check engine light comes on, your car stalls at stoplights, or you feel a vibration through the steering wheel. These aren’t "maybe" problems—they’re clear warnings. Replacing worn spark plugs is one of the cheapest fixes you can make, yet most drivers wait until the engine is misfiring badly or the car won’t start at all.
What’s worse, people often blame fuel pumps, sensors, or even the battery when the real issue is just a set of old spark plugs. They’re not glamorous, but they’re essential. A typical set lasts 30,000 to 100,000 miles, depending on the type and your driving style. If you do a lot of short trips in cold weather, they wear out faster. No need to guess—check your owner’s manual or bring your car in for a quick diagnostic. We’ve seen too many customers spend hundreds on unnecessary repairs only to find out their spark plugs were the root cause.
Fixing this isn’t complicated. You don’t need to be a mechanic. But ignoring it? That’s where the real cost starts. A new set of spark plugs costs less than a tank of petrol. The damage they cause if left alone? That’s a whole different price tag.
Below, you’ll find real-world guides on what happens when spark plugs go bad, how they affect your exhaust, why your car might be using more fuel, and how to tell if it’s the plugs—or something else. No fluff. Just what you need to know to keep your car running right.
