Spark plugs ignite the air–fuel mixture in every petrol engine cylinder. When they wear, the spark weakens and the engine pays for it.

How long do they last?

It depends on the type. Copper plugs may need replacing every 30,000 km or so, while iridium and platinum plugs can last 80,000–100,000 km or more. Follow the interval in your owner’s manual and use the plug specified for your engine.

Signs of worn plugs

• Rough idle or misfires
• Hard starting
• Poor fuel economy
• Hesitation or loss of power
• A flashing check-engine light

What to replace with them

Ignition coils and leads fail with age and can damage new plugs. If you are replacing plugs on a high-mileage engine, inspect the coils too. Browse spark plugs and ignition coils.

Tips for fitting

• Change plugs on a cold engine.
• Check the gap if the plug is not pre-gapped.
• Tighten to the specified torque – over-tightening can damage the cylinder head.
• Replace them as a full set.

Use the Vehicle Finder to find the right plugs for your vehicle.