🔧 Outback - Spark Plug Replacement

Changing the spark plugs on your Outback restores proper ignition, smoother running, easier starts, and better fuel economy. The flat-4 engine places the spark plugs low on both sides of the engine, so access is tight but manageable with the right extensions and patience.

Difficulty Level: Intermediate | Estimated Time: 2-3 hours

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⚠️ Safety & Precautions

• ⚠️ Let the engine cool completely before starting; spark plugs thread into aluminum cylinder heads and hot threads can strip.
• ⚠️ Disconnect the negative battery cable before working near ignition coils.
• ⚠️ Replace one spark plug at a time so coil locations do not get mixed up.
• ⚠️ Do not force the new spark plugs; cross-threading can damage the cylinder head.
• ⚠️ Use only a torque wrench for final tightening; over-tightening can crack the plug or damage the head.

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🔧 Required Tools

You'll need the following tools for this repair:

• 10mm socket
• 12mm socket
• 14mm thin-wall spark plug socket
• 3/8-inch drive ratchet
• 3/8-inch drive torque wrench
• 3-inch extension
• 6-inch extension
• 3/8-inch universal joint adapter
• Flathead screwdriver
• Needle-nose pliers
• Compressed air blow gun
• Spark plug gap gauge
• Magnetic pickup tool
• 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: 4
• Dielectric grease - Qty: 1 small tube

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📋 Before You Begin

• Park your Outback on level ground, set the parking brake, and let the engine cool fully.
• Open the hood and install a fender cover to protect the paint.
• Disconnect the negative battery cable using a 10mm socket.
• A universal joint adapter lets the socket bend slightly in tight spaces.
• A thin-wall spark plug socket is narrower than a normal socket so it fits inside the spark plug tube.
• Check the new spark plugs with a spark plug gap gauge; gap should be about 0.044 in if not already pre-set.
• Do not apply anti-seize unless the spark plug manufacturer specifically requires it; most iridium plugs are plated and installed dry.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Disconnect the Battery

• Use a 10mm socket to loosen the negative battery terminal clamp.
• Move the negative cable aside so it cannot touch the battery post.
• Start with a cool engine.

Step 2: Remove the Battery for Left-Side Access

• Use a 10mm socket to remove the battery hold-down nuts.
• Lift off the battery hold-down bracket.
• Carefully lift the battery out of the engine bay.
• Set the battery upright in a safe spot.
• Use a 10mm socket to remove the battery tray fasteners if extra hand room is needed.

Step 3: Remove the Air Intake Parts for Right-Side Access

• Use a flathead screwdriver to loosen the intake hose clamp at the air filter box.
• Use a flathead screwdriver to loosen the intake hose clamp at the throttle body.
• Use needle-nose pliers to release small hose clamps if any breather hoses are attached.
• Use a 10mm socket to remove the air intake duct or air box fasteners as needed.
• Move the intake parts out of the way to reach the ignition coils on the passenger side.

Step 4: Locate the Ignition Coils

• Find the four ignition coils, two on each side of the engine.
• Each ignition coil sits directly over one spark plug.
• An ignition coil is the small electrical part that sends high voltage to the spark plug.
• Work on only one coil and one spark plug at a time.

Step 5: Remove One Ignition Coil

• Press the electrical connector tab with your finger or a flathead screwdriver.
• Pull the connector straight off the ignition coil.
• Use a 10mm socket to remove the ignition coil retaining bolt.
• Twist the ignition coil gently by hand, then pull it straight out.
• Twist first, then pull.

Step 6: Clean Around the Spark Plug Hole

• Put on safety glasses.
• Use a compressed air blow gun to blow dirt away from the spark plug tube.
• Do not skip this step; dirt can fall into the cylinder when the plug is removed.

Step 7: Remove the Old Spark Plug

• Assemble a 14mm thin-wall spark plug socket, 3-inch extension, 3/8-inch universal joint adapter, and 3/8-inch drive ratchet.
• Place the socket fully onto the spark plug.
• Turn counterclockwise slowly with the 3/8-inch drive ratchet.
• Once loose, spin the spark plug out by hand using the extension.
• Lift the plug out with the 14mm thin-wall spark plug socket or a magnetic pickup tool.

Step 8: Inspect and Prepare the New Spark Plug

• Compare the old plug and new plug to confirm the thread length and tip shape match.
• Use a spark plug gap gauge to verify the new plug gap is about 0.044 in.
• Do not pry hard on iridium plug tips; the center electrode is delicate.
• Do not coat the threads unless the plug maker specifically says to use anti-seize.

Step 9: Install the New Spark Plug by Hand

• Place the new spark plug into the 14mm thin-wall spark plug socket.
• Attach only the 6-inch extension, with no ratchet at first.
• Turn the extension clockwise by hand until the spark plug threads smoothly into the cylinder head.
• If it feels tight right away, stop, remove it, and start again.
• Hand-starting prevents thread damage.

Step 10: Torque the New Spark Plug

• Attach the 3/8-inch drive torque wrench to the extension and spark plug socket.
• Tighten the spark plug to Torque to 18 Nm (13 ft-lbs).
• Do not add extra tightening after the torque wrench clicks.

Step 11: Reinstall the Ignition Coil

• Apply a small dab of dielectric grease inside the rubber boot end of the ignition coil.
• Push the ignition coil straight onto the new spark plug until fully seated.
• Install the ignition coil bolt with a 10mm socket.
• Tighten the ignition coil bolt to Torque to 8 Nm (71 in-lbs).
• Reconnect the electrical connector until it clicks.

Step 12: Repeat for the Other Three Spark Plugs

• Repeat Steps 5 through 11 for each remaining spark plug.
• Use the 14mm thin-wall spark plug socket, 3-inch extension, 6-inch extension, and 3/8-inch universal joint adapter as needed for each side.
• Keep your movements slow in the tight spaces near the frame rails.

Step 13: Reinstall the Air Intake Parts

• Reinstall the air box or intake duct using a 10mm socket.
• Reconnect any breather hoses using needle-nose pliers if clamps were removed.
• Tighten the intake hose clamps with a flathead screwdriver.
• Make sure the intake hose is fully seated so unmetered air cannot enter the engine.

Step 14: Reinstall the Battery

• Reinstall the battery tray using a 10mm socket if it was removed.
• Place the battery back into position.
• Install the battery hold-down bracket using a 10mm socket.
• Reconnect the negative battery cable using a 10mm socket.
• Tighten the terminal snugly, but do not over-tighten it.

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✅ After Repair

• Start your Outback and let it idle for a few minutes.
• Listen for a smooth idle with no misfire or popping sounds.
• Check that every ignition coil connector is fully clicked in place.
• Check that the intake hose clamps are tight and the air box is sealed.
• Take a short test drive and confirm smooth acceleration.
• If the battery was disconnected, reset the clock and radio presets if needed.
• If a check engine light appears, scan for codes before driving further.

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💰 DIY vs Shop Cost

Shop Cost: $250-$450 (parts + labor)

DIY Cost: $45-$100 (parts only)

You Save: $150-$350 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1.5-2.5 hours.

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🎯 Ready to get started?

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