How to Change Spark Plugs

Man holding spark plugs

Keep your engine in good working order. Here's how to replace spark plugs.

To some, a car's engine may seem like an impossibly complicated hunk of mystical machinery. While that's not too far from the truth for many modern engines, there are still some easily serviceable items on even the most high-tech cars. Spark plugs, especially, are among the easiest parts to replace in any given engine. All it requires is carefully following some basic steps and a handful of basic tools.

Before we dive into the step-by-step process, you might be wondering how often you need to change your spark plugswhat sort of spark plugs you should use, or whether you need to upgrade your spark plug wires or other ignition components. Fortunately, these questions are easy to answer. And don't forget, you may need to replace your spark plug wires every time you change your spark plugs depending on your driving style.

But chances are, if you're here, it's because you know it's time to change your spark plugs. So let's get started.

Vehicle System
Ignition, Charging, & Electrical Systems
Skill Level
Beginner

This is a good project for new DIYers

Time to Complete
1 hour
  1. Once you've gathered all of the tools you need, as well as the correct spark plugs for your car and spark plug wires (if necessary), you may want to drape an old blanket or towel over the fenders of your car so that you won't mar the paint as you lean into the engine bay. It's also good practice to disconnect the positive terminal on your car battery when working on anything electrical.

  2. Pro Tip

    Be sure to let your car's engine cool thoroughly before replacing your spark plugs, and keep any flammable blankets, towels, or shop cloths away from any surfaces that may still be warm. This will also ensure the new spark plugs are tightened correctly (heat expands the engine threads and limits torque).

  3. Thoroughly clean the area around your spark plugs. Once you remove the spark plug, you'll have an open hole directly into the inside of your engine, and any dirt or debris around the spark plug can fall straight in and cause serious wear or damage to your engine—something that should be avoided, for obvious reasons.

    You can use compressed air to blow the area clean, and/or a cleaner/degreaser spray and shop towels to loosen and remove any gunk around the spark plug. Be sure to wear eye protection if you'll be using compressed air or a spray cleaner.

    Once you have the area around each spark plug clear of any oil, dirt, or other debris, it's time to start the actual replacement process.

  4. Keep everything in order by removing a single spark plug wire from one spark plug at a time. This prevents you from reconnecting the wrong wire to the wrong plug when it's time to button everything back up.

  5. Once you've removed the first spark plug wire, fit the necessary combination of extensions and swivels to the spark-plug socket to comfortably fit the tool to the spark plug.

    Turn the spark plug counterclockwise until it comes free.

    Even though you cleaned around the spark plug thoroughly before beginning, take care not to knock any previously unseen debris into the now-open hole into your engine's interior.

  6. Once the spark plug is out, take the new spark plug and use the spark plug gap tool to check that there is a proper gap between the outer (hook-shaped) ground electrode and the center electrode. Most modern spark plugs are properly gapped from the factory, but shipping and handling can result in this small but crucial gap being tweaked, so it's always good to ensure the gap is correct before installing.

    If any adjustment is needed, gently open or close the gap until the tool just fits at the correct gap (which should be specified in your owner's manual).

  7. With the gap verified, carefully insert the plug into the open hole by hand. If your spark plug isn't factory treated with anti-seize, you can rub a small drop of anti-seize lubricant on the spark plug thread so it doesn't lock up from the heat. Gently start screwing the plug in with a clockwise rotation, ensuring the threads are properly mated.

    Once the spark plug is carefully started into the threads, continue tightening the plug down with the spark plug socket and ratchet/extension combination. Be very careful not to over-tighten your spark plugs! Just tighten it down until the spark plug's washer is firmly in contact with the shoulder of the threaded hole and the washer is slightly compressed.

  8. Pro Tip

    Be careful to avoid cross-threading the spark plug when re-installing, as any damage to the spark-plug threads could require costly repairs to your car's cylinder head.

  9. With the spark plug securely re-installed, reattach the plug wire by twisting slightly as you push the boot back down onto the exposed tip of the plug until you hear and feel a firm click. That means you've properly seated the plug wire. You can put a drop of dielectric grease inside the plug boot for better heat dissipation.

  10. Repeat the process in Steps 2 through 7 for each of your remaining spark plugs until you've replaced them all. If you're also replacing your spark plug wires, go back and do each one in the same order, one at a time. You'll notice that the spark plug wires vary in length according to their proper installation position, so be sure to match each wire up to the existing wire before removing the old one and replacing with the new wire. Repeat until all the wires are replaced.

    You're done! Before you celebrate, however, be sure to mark down the car's current mileage in your maintenance notebook, so you'll know when you need to change your spark plugs again.

Last updated August 18, 2017

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