Is your car running rougher than it used to? Does it miss, backfire or refuse to start? Does your fuel consumption seem higher? If your four-wheeled friend is suffering any of these problems it could be time to change your spark plugs.

Even if your car is running without problems, most mechanics recommend changing your spark plugs every 40,000 – 55,000 km.

What Do Spark Plugs Actually Do?

Spark plugs are basically a pair of electrodes which produce a high voltage spark that ignites the air/fuel mixture in the engine. This explosion drives the cylinder down and this force is eventually transferred to the wheels of your car, causing it to move. Without that spark the whole process of internal combustion couldn’t occur.

At the Shop

Spark plugs must be matched to your engine. So, when you buy your new plugs make sure you get the right sort by taking a note of the make, model, age and engine type of your car with you to the auto shop.

Safety First – You and Your Car

Disconnect the negative cable from your battery (usually the black one). This will prevent the chance of an electric shock.

Do not start work on your spark plugs until the engine is thoroughly cool. Working on a hot engine presents a burn risk to you and may also result in damage to the cylinder head.

A Note for the Novice

You can remove and replace one plug at a time, or remove all of them at once and then replace the set en masse. If you choose the latter option and you’re not that experienced in the garage, number each spark plug wire using masking tape and a marker pen before you start work. This way you’ll reconnect the right wire to the right plug.

Removing the Plugs

Equip yourself with a spark plug socket, extension rod, and ratchet (a spark plug socket wrench). Open the bonnet of your car and follow the first spark plug wire back to the cylinder head where the plugs are located.

Remove the wire from the plug by gently pulling on the “boot” (the rubber housing that fits over the top of the spark plug. Don’t pull on the wire itself as this could dislocate it from its connector.

Spark plugs sit in a well in which dirt and debris can collect. It is important not to let any of this fall into the engine when the plug is removed, so clean the area with a rag or, even better, a can of compressed air.

Place your spark plug socket wrench over the plug and turn counter clockwise until the plug is fully disengaged from its bore. Remove the plug.


The size of the gap between the electrodes of a spark plug is crucial to it’s, and your car’s, performance. Many spark plugs today are pre-gapped so that no adjustment is necessary. However, if you do need to gap your plugs, refer to your car’s manual for the correct sizing. Use a sizing gauge and be gentle when bending out, or tapping in, the ground electrode (the curved one at the very tip of the spark plug).

Inserting the Plugs

Screw in the new plug by hand. A length of rubber hose fitted over the body of the plug can help you manoeuvre it into position in confined spaces. If any resistance is felt stop immediately, remove the plug and try again.

Tighten the plug carefully with the socket wrench – stripping the thread on the cylinder head could turn a money-saving DIY task into an expensive repair.

Rub a little dielectric compound over the end of the plug to improve electrical connectivity and discourage corrosion and then replace the spark plug wire.

Improved Performance

Replacing spark plugs is a job almost any handyman or woman can do. By doing it yourself you’ll be saving money at the same time you’re improving the performance of your car. And you’ll save money again because your car will be more fuel efficient and your petrol bill will be smaller.



Learn more about spark plugs with this video.

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