How to Replace Worn Subaru Spark Plugs

Spark plugs play a crucial role in the combustion process of your Subaru’s engine, providing the necessary spark to ignite the air-fuel mixture. Over time, spark plugs can wear out and affect engine performance, fuel efficiency, and overall reliability. Knowing how to replace worn spark plugs is essential for maintaining optimal engine performance in your Subaru. In this article, we will provide step-by-step instructions and expert guidance on how to replace worn spark plugs in your Subaru, ensuring a smooth-running engine.

  1. Gather the Necessary Tools and Materials

Before starting the spark plug replacement process, gather the required tools and materials. You will typically need a ratchet or spark plug socket, a spark plug gap tool, a torque wrench, dielectric grease, and a new set of spark plugs specifically designed for your Subaru model. Consult your owner’s manual or speak with a professional technician to ensure you select the correct spark plugs for your Subaru.

  1. Prepare the Vehicle

Ensure your Subaru’s engine is cool before proceeding with the spark plug replacement. Park the vehicle on a level surface and engage the parking brake for safety. Open the hood and locate the spark plug wires or ignition coils, depending on your Subaru’s configuration.

  1. Remove the Spark Plug Wires or Ignition Coils

If your Subaru is equipped with spark plug wires, gently twist and pull the wires to disconnect them from the spark plugs. Avoid pulling on the wires themselves, as this can damage them. For Subarus with ignition coils, carefully remove the retaining bolts or screws securing the coils in place and disconnect the electrical connectors.

  1. Remove the Old Spark Plugs

Using a ratchet or spark plug socket, loosen and remove the old spark plugs from the cylinder head. Turn the socket counterclockwise to unscrew the spark plugs. Inspect the old spark plugs for signs of wear, such as worn electrodes or excessive carbon deposits. If the spark plugs appear damaged or worn out, it is recommended to replace them.

  1. Gap and Install the New Spark Plugs

Check the gap of the new spark plugs using a spark plug gap tool. Refer to your Subaru’s owner’s manual or consult a professional technician for the correct gap specification. Adjust the gap as necessary by gently bending the ground electrode. Apply a small amount of dielectric grease to the inside of the spark plug boots or the top of the ignition coils to aid in future removal.

Carefully thread the new spark plugs into the cylinder head by hand to avoid cross-threading. Once hand-tight, use a torque wrench to tighten the spark plugs to the manufacturer’s specified torque value. Over-tightening can damage the threads or break the spark plugs, while under-tightening can cause misfires.

  1. Reinstall Spark Plug Wires or Ignition Coils

If you have spark plug wires, reconnect them to the appropriate spark plugs by pushing them firmly onto the spark plug terminals. For ignition coils, reattach the electrical connectors and secure the coils in place using the retaining bolts or screws.

  1. Repeat the Process for Each Cylinder

Repeat the steps outlined above for each cylinder in your Subaru’s engine. It is recommended to replace all the spark plugs at once, even if only one or a few appear worn. This ensures consistent performance and avoids the need for future individual replacements.

Replacing worn spark plugs in your Subaru is essential for maintaining optimal engine performance and fuel efficiency. By following the step-by-step instructions outlined above and using the correct tools and materials, you can replace the spark plugs effectively. Contact our technicians at Competition Subaru for more details!