How Much Do Spark Plugs Cost to Replace?

Spark plug replacement costs in Australia:

• 4-cylinder cars: $80–$200
• 6-cylinder cars: $150–$350
• 8-cylinder cars: $200–$400
• European/luxury vehicles: $250–$500+

The parts are cheap ($5–$25 per plug), but labour varies significantly depending on engine layout. Some engines (like the Subaru boxer or certain V6s) have plugs that are extremely difficult to access.

When Should You Replace Spark Plugs?

Replacement intervals depend on the plug type:

• Copper plugs: Every 30,000 km
• Platinum plugs: Every 60,000–80,000 km
• Iridium plugs: Every 80,000–120,000 km
• Double platinum/iridium: Up to 150,000 km

Check your owner's manual for the specific recommendation. Don't go by 'they still look okay' — spark plug gap increases with use, causing weaker spark even when the plug looks fine.

Symptoms of Worn Spark Plugs

Signs your plugs need replacing:

• Rough idle or engine vibration
• Misfires (P0300-P0312 codes)
• Sluggish acceleration
• Poor fuel economy
• Hard starting, especially in cold weather
• Engine surging or hesitating
• Failed emissions test

Worn plugs don't always trigger a check engine light. If your car has over 80,000 km on the original plugs, replace them as preventive maintenance.

Can You Replace Spark Plugs Yourself?

On most 4-cylinder engines, this is a straightforward DIY job:

1. Let the engine cool completely.
2. Remove the ignition coils or spark plug wires.
3. Use a spark plug socket (16mm or 21mm, depending on the engine) with an extension.
4. Remove the old plugs and check the gap on the new ones (or buy pre-gapped plugs).
5. Install the new plugs hand-tight, then torque to specification.
6. Reinstall the coils or wires.

Tools needed: Spark plug socket, ratchet, extension bar, torque wrench, gap gauge.

Difficulty: Easy on inline-4 engines. Moderate to difficult on V6/V8 engines where rear plugs are hard to reach.

What Type of Spark Plug Should You Buy?

Always match the manufacturer's specification. Check your owner's manual or look up the part number.

General guidance:

• Use the same type that came from the factory (copper, platinum, or iridium).
• Upgrading from copper to iridium is fine and extends replacement intervals.
• Don't downgrade from iridium to copper — the engine is calibrated for the finer electrode.
• NGK and Denso are the most widely used OEM spark plug brands in Australia.
• Avoid cheap no-brand plugs — the electrode material and quality control matter.