Spark Plugs: What You Need to Know

Spark plugs screw into the top of an engine's cylinders to create the electric spark required to ignite the compressed air-fuel mixture in gas-powered engines. The right type of plug and the size of the gap between the electrodes at the tip are specified by the automaker, and using the right ones are crucial to proper performance.

How do I know it's time to replace my spark plugs?
An engine that misfires -- meaning the spark plugs fire at the wrong time -- could be the result of worn or fouled plugs. Other indications of worn spark plugs are poor fuel economy, hard starting and sluggish acceleration. Engine computers these days do a remarkable job of compensating for worn plugs, so they might not be the main or only cause of engine problems.

How often should I replace my spark plugs?
Unless your car is hard to start, idles roughly, accelerates sluggishly or gulps gasoline, you'll probably get little benefit from replacing the spark plugs before the time or mileage interval recommended by your car's manufacturer. Some automakers recommend replacing spark plugs as soon as 60,000 miles, while others say 100,000 miles or later. Spark plugs use precious metals such as platinum and iridium that extend their useful lives.

Why do I need to change my spark plugs?
You might not need to; they should be changed only if they're fouled by gas or oil, cause the engine to misfire, or are diagnosed as the cause of hard starting, poor acceleration or low fuel economy. Of course, if you've hit the mileage limit, have your mechanic investigate.

How much should I pay?
The cost of repairs can depend on where you are as much as it does on what you need fixed. To get an estimate for your repair, go to our estimator, plug in your car's year, make and model information, add your ZIP code, and choose the repair you need. We'll give you a range for what your repairs should cost in your area.