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How do I change spark plugs?

How do I change spark plugs?

Spark plugs are necessary accessories for the operation of internal combustion engines in modern cars. Like everything else, these accessories wear out, but the problem is that car spark plugs are components with a limited lifespan. Therefore, they need to be replaced on a regular basis. Thirty years ago, automotive professionals recommended replacing spark plugs every 10,000 to 15,000 km, but today, depending on the model, they are replaced every 30,000 to 120,000 km.

How can you recognize the first signs of wear in your spark plugs?

The car has difficulty starting. Experienced drivers are often tempted to attribute this problem to a faulty spark plug. However, it's best to take the car to a mechanic and replace the spark plug, as several factors can affect an engine's ignition system.

Your car's engine should make a steady sound. If you notice that your engine is racing or making more noise than usual, this could be a sign of a problem with your spark plugs.

Before you blame your battery, remember to check the condition of your spark plugs. Dirty plugs prevent the spark needed to ignite the air-fuel mixture needed to start your engine.

If your car's engine misfires, it may be because your spark plugs are prematurely plugged. Carbon deposits on your engine's spark plugs affect the cylinders in the engine block, causing them to misfire.

You notice that your fuel consumption is higher than usual. Dirty or damaged spark plugs can significantly increase your fuel consumption. You find it hard to accelerate under normal traffic conditions; your spark plugs probably need to be replaced.

Acceleration is slow. When a spark plug begins to fail, you may feel that the vehicle has difficulty accelerating. In this case, even though there's a good chance that the spark plug is worn, it's still best to visit a shop because slow acceleration can also be caused by faulty fuel filters, a dirty or clogged fuel injector, or a faulty oxygen sensor.

When to change your spark plugs?

When you check your spark plugs, it's easy to see if they need to be replaced:

  • If your spark plugs are black, it means there is poor combustion and/or the plug is worn.
  • A broken spark plug should be replaced immediately as it can destroy the piston, which can be expensive to repair.
  • Any type of deposit, whether oil or even just a simple black deposit, is a warning sign that a spark plug is starting to wear out and should be replaced.

Of course, make sure that your engine is at a standstill and that the negative terminal of your battery has been disconnected for a long time before you try to check or replace anything in your engine.

How do I change spark plugs?

  • Step 1: Get your tools ready. You'll need a torque wrench, a spark plug wrench, a ratchet, a vacuum and/or air blower, a screwdriver, and a clean cloth.
  • Step 2: Turn off the engine. This may seem obvious, but allow the engine to cool before working on it and opening the hood to avoid burning yourself.
  • Step 3: Locate the spark plugs. Check the vehicle manual for their exact location. Make sure the new spark plugs are the same type as the old ones and memorize the location of the components.
  • Step 4: Remove the spark plugs. Disconnect the negative battery post and remove any protective covers. Take the opportunity to breathe in, blow out, and clean the area around the spark plugs to prevent dirt and debris from falling into the spark plug base or the engine. Remove the spark plugs one at a time, making sure to mark which wire corresponds to which plug.
  • Step 5: Check the condition of the electrodes: they should be gray-brown and free of deposits. Check that the new spark plugs fit your engine perfectly. Only the electrode should be different.

  • Step 6: Adjust the gap: even if it is preset at the factory, the correct electrode gap is the key to perfect combustion. Use a set of shims (value indicated on the box) to check this. If necessary, you can adjust it by turning the ground electrode slightly without levering the center electrode.
  • Step 7: Install new spark plugs. Thread the new spark plugs into the engine by hand, taking care not to damage or overtighten them. You can use a socket extension, and some spark plugs are equipped with protectors to hold them in place. Check the torque specifications for your vehicle and use a torque wrench to tighten the spark plugs. Finally, replace the caps and reconnect the battery.
  • Step 8: Replace the ignition coils and reconnect the connectors. The rail must be installed after the spark plugs are replaced. Start the engine and make sure it runs properly before replacing the cylinder head cover.


It is impossible to run a gasoline engine without spark plugs. These small components, which produce the spark that ignites the air-fuel mixture, are quite fragile and their wear or malfunction is often the cause of engine problems. That's why it's important to take care of your spark plugs, checking their condition regularly and replacing them at the recommended intervals.

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