How to replace spark plugs
Worn spark plugs cause misfires, hesitation and poor fuel economy. Replacement intervals vary from about 30,000 km for copper plugs to over 100,000 km for iridium plugs.
Tools
- Spark plug socket with rubber insert
- Ratchet and extensions
- Torque wrench
- Gap gauge (if plugs need gapping)
- Compressed air
Parts & materials
- Correct spark plugs for the engine (check the owner's manual or a parts catalogue)
Step by step
- Work on a cold engine: aluminium cylinder heads can be damaged removing plugs from a hot engine.
- Remove the engine cover and disconnect the ignition coils or plug leads one at a time to keep the order.
- Blow away dirt around each plug well before removing the plug, so nothing falls into the cylinder.
- Unscrew the plug. Check its condition: oily, black or white deposits tell you about engine health.
- Check the gap on the new plug if the manufacturer requires it; many pre-gapped iridium plugs should not be adjusted.
- Start the new plug by hand to avoid cross-threading.
- Tighten to the specified torque.
- Refit the coils or leads, making sure they click home.
- Start the engine and check for smooth running and no warning lights.
Safety: Do not use anti-seize unless the plug maker recommends it; it changes the effective torque.
Symptoms this can fix
Procedures differ between vehicles. Check your vehicle's service information for specifications, torque values and any special steps.