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How Often Should You Change Spark Plugs? Signs, Cost & How to Guide

spark plug on blue background

Unless you own an electric vehicle, spark plugs will be an important part of your driving life. Luckily, they are designed to last you a long time, meaning you will rarely need to replace them. This does not mean random damages cannot occur, which may require replacement sooner. That said, it’s advisable to change the spark plugs once the car has covered at least 30,000 miles.

Depending on your car usage, you should have the plugs checked every 20,000–40,000 miles. In this article, we will take a look at spark plugs, how often you should replace them, and the negative impact they may have on your car if not replaced at the right times.

car and road divider

What Is a Spark Plug?

A spark plug is a device used to deliver a spark or electric current to the combustion chamber from the ignition system. This allows for the ignition of compressed air, which means a spark plug helps get your engine started.

hand showing four spark plugs
Image Credit: mister_Art, Shutterstock

Benefits of a Spark Plug

Spark plugs are used to aid in the car starting up smoothly and quickly. They also keep the car in tip-top condition, which helps smooth the acceleration. At the same time, they reduce the car’s fuel consumption by up to 30%. According to the EPA, spark plugs help reduce carbon emissions as well.

Signs That You Need to Replace Your Spark Plugs

You may have forgotten about getting your car a tune-up and replacing the old worn-out spark plugs. The following signs may act as a subtle reminder to visit your mechanic for a replacement.

  • Misfiring Engine: If you experience the engine’s pace faltering and catching back up while driving, this may mean you have worn-out spark plugs. There may be other reasons, such as inferior fuel or bad coil plugs, which may be a good indication you should get it checked out. When a vehicle misfires, it means that it is sending raw fuel to the exhaust, which may result in damaging the catalytic converter.
  • The Car Is Not Starting: There are a couple of reasons why your car is not starting, one of which may be a faulty spark plug. While fuel or the battery may also come into play, it is recommended that you also check the spark plug. A faulty one will cause the car’s engine to work harder to compensate, especially when the weather is too cold.
  • Rough or Noisy Idling: While driving, you may notice the car’s engine rattling, even over the normal noise from a moving car. This may also point to a faulty spark plug.
  • Struggling to Accelerate: If the spark plug is having problems igniting the fuel-air mixture, the car will have acceleration issues. This will be felt through the car by seeming to stutter while accelerating.
  • Increased Fuel Consumption: An engine will not be able to effectively burn fuel to provide the necessary power to propel the car. As previously seen, a faulty spark plug will end up sending raw fuel to the exhaust, which will result in increased fuel consumption and, in turn, cause you to make more trips to the gas station.
  • Ignition Coil Failure: Worn-out spark plugs can cause an ignition coil failure. An ignition coil creates a high-voltage impulse to generate an electrical spark in the engine. The car will give you the signal to check your engine to determine what the problem is.
  • Spark Plugs Change Color: Your car’s spark plugs may be old, but if they have a tan or gray color, it means they are still fine and usable. However, if you find some oily deposits clogging them, it may be a sign that there is some oil in the combustion chamber, and that leads to trouble. Oily deposits occur when the engine does not get enough time to heat up between oil changes. Address oil leak issues immediately to avoid further complications.
  • Overheated Spark Plugs: If the spark plugs are overheating or melting, it means that the cylinder is getting overheated. This may be due to either over-cooling of the air-fuel mixture or the cooling system not working.

How Often Should You Change a Vehicle’s Spark Plugs?

Most cars have a manual with information about spark plugs. Most manufacturers advise you to change the spark plugs after the car covers at least 30,000 miles. If you bought a used car with no manual, check the spark plugs after you start noticing some of the common problems associated with worn-out spark plugs.

In case you notice something off with your car engine, especially in connection to starting and acceleration issues, first check the spark plugs under the hood of the car.

If the spark plugs seem to have some dirt, it may be that they have an oil leak or carbon deposits. If they are completely worn out or damaged, it may mean that the engine is operating at excess heat levels.

However, always get your spark plugs checked every 20,000–40,000 miles, depending on how much you use the car. For high-performance vehicles, you will need to check the spark plugs more often.

spark plug

How Much Does It Cost to Change Spark Plugs?

The good news is that changing your spark plugs won’t cost you too much. They typically cost between $16–$100 out of pocket.

If you are new to car repairs and have no idea how to change the spark plugs, hire a professional. With professional labor included, you may part with $40–$150. However, with a bit of experience and the right tools, you can do the job and cut down on costs.

How to Change Spark Plugs

Before you attempt a DIY spark plug change, check the kind of spark plug you need for your car. You will need the following tools:

Tools & Materials
  • Rags to wipe up the grease stains
  • Needle-nose pliers
  • Torque wrench
  • Swivel socket
  • Spark plug wire puller
  • Gap gauge
  • Socket wrench

First, remove the covering on the spark plugs and the air cleaner component. Eliminate any risk of dust getting into the cylinders after removing the spark plugs. You can do this by blowing on the engine to remove any dust and dirt particles.

Pull on the locking tab by removing the ignition coil. Use the connector to disconnect the coil bolt to be able to remove the boot component and the whole coil. Next, use the spark plug wire to remove the boot.

Allow the car’s engine to cool down before you remove the spark plugs. Use your wire puller to position the boot far down at the end of the plug. You can then use the swivel socket to remove the spark plugs.

Before installing the new spark plugs, ensure you space them according to the manufacturer’s recommendations. Use a torque wrench to ensure you have the required amount of torque, as too much will misshape the spark plugs.

Finally, add some lube to the boot of the spark plugs before reinstalling the coil to prevent misfiring and to make any subsequent changes a bit easier. Reinstall the coil’s electrical connector, then bolt and cover in the air cleaner.

Gapping Out a Spark Plug

Gapping a spark plug means leaving a sufficient gap between the center and side electrodes so that arcing occurs at the required voltage to ensure efficient engine performance.

Nowadays, spark plugs come pre-gapped. However, they will need double-checking before installing them in the car.

close up hand holding a spark plug
Image Credit: robertdiffin, Pixabay

Should Spark Plugs Be Replaced as a Set?

There is a common concern about whether spark plugs should be replaced as a set, especially when only one is spoilt or damaged. The answer is yes, spark plugs should all be replaced in case one is spoilt. In fact, they come in sets to prevent any problems arising from the difference from switching only one spark plug.

In older cars, spark plugs may be removed and adjusted from time to time and still work efficiently. However, for newer models of vehicles, this is not usually ideal.

car and road divider


How is your car performing? Do you suspect that the car has some spark plug problems? With the information available, you are well set to diagnose spark plug problems and get them replaced. It will not always be a spark plug causing the issues, but ruling spark plugs out in the first place will help arrive at the real problem faster.

Featured Image Credit: Thor_Deichmann, Pixabay


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