How Often Do You Need to Replace Spark Plugs?

By Staff WriterLast Updated Jun 24, 2020 6:49:37 PM ET
Spark plugs attached to the electrodes of an engine
CC0/olafpictures/Pixabay

Spark plugs screw into the cylinder of your engine and connect to the ignition system. Electricity from the ignition system flows through the plug and creates a spark. This ignites with the fuel-and-air mixture in the cylinder to create an explosion and power the engine. Spark plugs are important for starting the car, but they must also continue to fire at set intervals to keep the engine going. When spark plugs wear out, they don't fire at the proper times and don't work as they should. Fortunately, spark plugs are durable and last for thousands of miles before they need maintenance. If you're having trouble determining if it's time to replace your spark plugs, use these guidelines to help.

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Manufacturer Guidelines

How long spark plugs last depend on the vehicle and the quality of the spark plugs. Some wear out after 60,000 miles and others keep going for 120,000 miles. As with other car maintenance tasks, it's best to refer to the owner's manual or manufacturer guidelines for the most accurate information. Even if you don't notice any problems, you should replace the spark plugs at these designated intervals to ensure your vehicle continues running optimally.

Check Engine Light

Though not always an accurate predictor of spark plug performance, the check engine light is a good place to start. If your spark plugs aren't working as they should, they can trigger the sensor that causes the light to come on. Many auto stores and garages offer free check engine light diagnostics, so it's worth a quick trip to find out what the problem is as soon as possible.

Problems Cranking the Car

One of the first signs that it's time to replace spark plugs is that you have trouble starting the car. The purpose of the spark plug is to create the spark that ignites the fuel in the engine. When the spark plugs wear out, they do not perform this job efficiently and cause problems cranking the engine.

Poor Fuel Economy

When your spark plugs are worn out, you'll notice a considerable drop in fuel efficiency. Misfiring spark plugs do not use up all of the fuel in the cylinder and it's wasted. It can reduce your fuel economy by as much as 30 percent, according to Firestone.

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Engine Idles Roughly

A finely tuned engine purrs quietly. Rattling, sputtering and knocking sounds often mean that your spark plugs are misfiring. Additionally, you may feel jerking or bumping when your car idles at a stop light.

Trouble Accelerating

To go along with your fuel not being used efficiently, you'll also notice that your car has less power. It might hesitate when you take off from a stop or be slow to accelerate. If your car is sluggish and not driving like it usually does, it might be time for spark plug replacement.

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If you take your car in for routine maintenance and tune-ups, auto mechanics will check the correct spark plug gap in addition to other components, such as oil, oil filter, air filter and more. Your mechanic can tell if your spark plugs are wearing out and replace them for you before you start experiencing any serious symptoms.