How To Change Auto Spark Plugs | HowStuffWorks

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Here you see a socket wrench with a spark plug socket, a pair of spark plugs and a gap gauge tool. © iStockphoto.com/skhoward

You'll need just a few tools to change out the spark plugs on your car. The most important tool is a socket wrench with an extension and a spark plug socket. Spark plug sockets come in two sizes: 5/8 inches and 13/16 inches. Most spark plug sockets have a rubber insert that holds the plug snugly in place.

You may also need a universal joint if your spark plugs are difficult to reach. Universal joints are articulated joints that allow you to turn the wrench in one axis and convert this motion into a rotation around another axis. If you can't maneuver a wrench and extension in the space around your spark plugs, a universal joint may help.

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When replacing spark plugs, it's important to avoid over-tightening the plugs. Tightening a spark plug too far could damage the plug or the threads in the cylinder head. Use a torque wrench to make sure you don't over-tighten your plugs. Torque wrenches have a gauge that displays the torque you've applied when turning the wrench.

While most modern spark plugs come pre-gapped from the manufacturer, a gapping tool is good to have on hand. You use a gapping tool to make sure the gap between the spark plug's center electrode and the ground electrode above it are the right distance apart. This is where the spark fires on your spark plug.

You may also want to have on hand a pair of boot pliers, a length of rubber tube, a clean rag, some rubbing alcohol, a tube of anti-seize and compressed air or a wet/dry vacuum on hand. These items aren't critical for a basic spark plug replacement job but can help ensure that the process goes smoothly.

We'll walk you through the correct steps on the next page.

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