🔧 CX-50 - Spark Plug Replacement

Replacing the spark plugs restores strong ignition, smooth idle, and good fuel economy. On your CX-50, the plugs sit under the ignition coils on top of the engine, so access is straightforward with basic hand tools.

Difficulty Level: Intermediate | Estimated Time: 1.0-2.0 hours

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⚠️ Safety & Precautions

• 🔥 Work on a fully cool engine to avoid burns and damaged threads.
• 🔌 Disconnect the negative battery cable to prevent accidental shorting.
• 🧼 Keep dirt out of the spark plug holes; blow them out before removing plugs.
• 🧵 Start new plugs by hand to prevent cross-threading.

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🔧 Required Tools

You'll need the following tools for this repair:

• 10mm socket
• 3/8" drive ratchet
• 3/8" drive torque wrench (5-30 Nm range)
• 16mm spark plug socket (5/8") with rubber insert
• 3/8" drive extension set (3" and 6")
• Trim clip tool
• Compressed air or electric duster
• Feeler gauge (metric or inch)
• Nitrile gloves
• Safety glasses

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Iridium spark plugs (OEM-equivalent) - Qty: 4
• Dielectric grease - Qty: 1

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📋 Before You Begin

• Park on level ground, shift to Park, and set the parking brake.
• Let the engine cool completely (warm aluminum threads can strip).
• Use a 10mm socket to disconnect the negative battery terminal and isolate it so it can’t spring back.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover

• Pull the engine cover straight up to release the grommets (use a trim clip tool gently if it’s stubborn).

Step 2: Unplug and remove the ignition coils

• On one coil at a time, press the connector lock tab and unplug the coil.
• Use a 10mm socket and 3/8" ratchet to remove the coil hold-down bolt.
• Twist the coil slightly, then pull it straight up and out. Do one cylinder at a time.
• When reinstalling coil bolts: Torque to 8 Nm (71 in-lbs).

Step 3: Clean the spark plug wells

• Use compressed air or electric duster to blow debris out of the plug hole before loosening the plug.
• This prevents dirt from falling into the cylinder.

Step 4: Remove the old spark plugs

• Use a 16mm spark plug socket (5/8"), extension, and 3/8" ratchet to loosen and remove the plug.
• Lift the plug out with the spark plug socket (the rubber insert should hold it).

Step 5: Check and prepare the new spark plugs

• Confirm the new plugs match the old ones (reach and seat style).
• Check the gap with a feeler gauge: Gap spec: 1.0-1.1 mm (0.039-0.043 in).
• Do not bend the fine-wire tip on iridium plugs; if the gap is off, exchange the plug.
• Do not apply anti-seize to Mazda-style plated plug threads unless the plug maker specifically requires it.

Step 6: Install and torque the new spark plugs

• Thread the new plug in by hand using the extension and spark plug socket only (no ratchet) until it seats.
• Use a 3/8" torque wrench to tighten: Torque to 15-20 Nm (11-15 ft-lbs).
• If it doesn’t thread easily, stop and restart.

Step 7: Reinstall ignition coils and connectors

• Add a tiny smear of dielectric grease inside the coil boot (the rubber boot only, not on the plug tip).
• Push the coil straight down until fully seated.
• Install the coil bolt with a 10mm socket, then tighten with a torque wrench: Torque to 8 Nm (71 in-lbs).
• Reconnect the electrical connector until it clicks.

Step 8: Reinstall engine cover and reconnect the battery

• Reinstall the engine cover by aligning the grommets and pressing straight down.
• Reconnect the negative battery terminal using a 10mm socket.

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✅ After Repair

• Start the engine and listen for a smooth idle (no shaking or misfire).
• If the check engine light comes on or it runs rough, recheck coil connectors and coil seating.
• Take a short test drive, then recheck for any warning lights.

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💰 DIY vs Shop Cost

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

DIY Cost: $60-$140 (parts only)

You Save: $190-$310 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1.0-1.5 hours.

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🎯 Ready to get started?

HowToo makes it easy: same-day/2-day shipping on every part, plus all the tools and specialty tools you need! Check out the parts and tools sections below to add everything to your cart.