🔧 Spark Plugs - Replacement

Changing the spark plugs on your Outback helps restore smooth idle, strong acceleration, and proper fuel economy. The 3.6L flat-six engine has three spark plugs on each side, and space is tight, so patience and the right extensions are important.

Difficulty Level: Intermediate | Estimated Time: 2-4 hours

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⚠️ Safety & Precautions

• ⚠️ Let the engine cool completely before starting; spark plugs thread into aluminum cylinder heads that can be damaged when hot.
• ⚠️ Disconnect the negative battery cable before unplugging ignition coils.
• ⚠️ Keep dirt out of the spark plug wells; debris can fall into the engine when plugs are removed.
• ⚠️ Start each new spark plug by hand only; cross-threading means the plug is not going in straight and can damage the cylinder head.
• ⚠️ Do not use anti-seize unless the spark plug manufacturer specifically requires it; most modern plugs are coated from the factory.

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🔧 Required Tools

You'll need the following tools for this repair:

• 10mm socket
• 12mm socket
• 14mm spark plug socket
• 3/8-inch ratchet
• 3/8-inch torque wrench
• 3-inch 3/8-inch drive extension
• 6-inch 3/8-inch drive extension
• 3/8-inch universal joint adapter
• Flat-blade screwdriver
• Needle-nose pliers
• Compressed air nozzle
• Spark plug gap gauge
• Dielectric grease
• Fender cover
• Nitrile gloves
• Safety glasses

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Iridium spark plugs - Qty: 6
• Intake duct clamp or hose clamp - Qty: as needed

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📋 Before You Begin

• 🅿️ Park your Outback on level ground, shift to Park, and set the parking brake.
• ❄️ Let the engine cool for at least 2 hours if it was recently driven.
• 🔋 Use a 10mm socket to disconnect the negative battery cable and move it aside so it cannot touch the battery post.
• 🧽 Clean around the intake ducts and ignition coil areas before disassembly.
• 📏 Check the new plug gap with a spark plug gap gauge. The factory gap is typically about 0.039-0.043 in. Do not force-adjust fine-wire iridium tips unless necessary.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the Engine Cover

• Use your hands to lift the plastic engine cover straight upward from its rubber mounts.
• Set it aside where it will not get stepped on.
• Pull evenly to avoid cracking it.

Step 2: Disconnect the Negative Battery Cable

• Use a 10mm socket to loosen the negative battery terminal nut.
• Lift the negative cable off the battery post and tuck it safely to the side.
• Wait 2 minutes before unplugging ignition coil connectors.

Step 3: Remove the Passenger-Side Air Intake Duct

• Use a flat-blade screwdriver to loosen the air duct clamp at the throttle body side if it blocks access.
• Use a 10mm socket to remove any intake duct mounting bolts.
• Disconnect small clips or hoses carefully with needle-nose pliers if needed.
• Move the duct out of the way to access the passenger-side ignition coils.

Step 4: Remove Driver-Side Access Obstructions

• Use a 10mm socket to loosen or remove any plastic intake resonator brackets that block the driver-side coil area.
• Use a flat-blade screwdriver to release any plastic retaining clips gently.
• Move wiring harnesses only enough to create working room; do not pull hard on the wires.

Step 5: Clean Around the Ignition Coils

• Put on safety glasses.
• Use a compressed air nozzle to blow dirt away from each ignition coil and spark plug well.
• A spark plug well is the deep tube where the spark plug sits inside the cylinder head.

Step 6: Unplug One Ignition Coil

• Press the locking tab on one ignition coil connector with your thumb or a flat-blade screwdriver.
• Pull the connector straight back; do not pull on the wires.
• Work on one spark plug at a time so parts do not get mixed up.

Step 7: Remove One Ignition Coil

• Use a 10mm socket and 3/8-inch ratchet to remove the ignition coil retaining bolt.
• Twist the coil slightly by hand, then pull it straight out of the spark plug well.
• Inspect the rubber boot for oil, cracks, or carbon tracking, which looks like a thin black burn line.
• For reinstallation later, tighten the ignition coil bolt to Torque to 8 Nm (71 in-lbs).

Step 8: Remove the Old Spark Plug

• Use a 14mm spark plug socket, 3-inch extension, and 3/8-inch ratchet to loosen the spark plug.
• Use a 6-inch extension or 3/8-inch universal joint adapter where space is tight.
• A universal joint adapter lets the socket angle slightly in tight spaces.
• Turn counterclockwise slowly until the plug is loose, then remove it carefully.
• If the plug feels stuck, stop and tighten it slightly, then loosen again slowly.

Step 9: Install the New Spark Plug by Hand

• Place the new iridium spark plug into the 14mm spark plug socket.
• Use only the extension by hand at first, with no ratchet attached.
• Turn clockwise gently until the plug is seated by hand.
• If it does not turn smoothly, remove it and start again.
• Hand-starting prevents expensive thread damage.

Step 10: Torque the New Spark Plug

• Attach the 3/8-inch torque wrench to the 14mm spark plug socket and extension.
• Tighten the spark plug to Torque to 18 Nm (13 ft-lbs).
• Do not overtighten; the cylinder head is aluminum.

Step 11: Reinstall the Ignition Coil

• Apply a small amount of dielectric grease inside the end of the ignition coil boot.
• Dielectric grease helps seal out moisture but does not conduct electricity.
• Push the ignition coil straight onto the new spark plug until seated.
• Use a 10mm socket and torque wrench to tighten the coil bolt to Torque to 8 Nm (71 in-lbs).
• Reconnect the electrical connector until it clicks.

Step 12: Repeat for the Remaining Five Spark Plugs

• Repeat Steps 6-11 for the other five spark plugs.
• Use the 14mm spark plug socket with the 3-inch extension for easier plugs.
• Use the 6-inch extension and 3/8-inch universal joint adapter for tighter rear plugs.
• Keep each ignition coil matched to its original cylinder if possible.

Step 13: Reinstall Intake Ducts and Brackets

• Use a 10mm socket to reinstall any intake duct mounting bolts.
• Tighten small intake duct bolts snugly to Torque to 7 Nm (62 in-lbs) if applicable.
• Use a flat-blade screwdriver to tighten hose clamps securely.
• Reconnect any hoses or wiring clips removed for access.

Step 14: Reinstall the Engine Cover

• Line up the engine cover with its rubber mounts.
• Press down by hand until it snaps into place.

Step 15: Reconnect the Battery

• Place the negative battery cable back onto the battery post.
• Use a 10mm socket to tighten the terminal nut snugly.
• Do not overtighten the battery terminal.

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✅ After Repair

• ✅ Start the engine and let it idle for 2-3 minutes.
• ✅ Listen for misfires, ticking, or hissing noises from loose intake ducts.
• ✅ If idle is rough at first, let the engine stabilize after the battery reconnect.
• ✅ Test drive your Outback for 10-15 minutes and check that acceleration feels smooth.
• ✅ Recheck that all ignition coil connectors and intake hoses are fully seated.
• ✅ If the check engine light flashes, stop driving and recheck coil connectors immediately.

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💰 DIY vs Shop Cost

Shop Cost: $450-$750 (parts + labor)

DIY Cost: $90-$180 (parts only)

You Save: $270-$660 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 2-3 hours.

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🎯 Ready to get started?

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