Engine · Car

Replace your spark plugs

On most four-cylinder petrol engines the plugs sit under the coils on top of the engine.

Time 45 minDifficulty ManageableAt a garage, this job costs £55 – £190

Tools

  • Spark plug socket (16 or 14 mm, with rubber insert)
  • Extension and ratchet
  • Torque wrench
  • Air blower or brush

Parts

  • Set of plugs to the exact manufacturer reference

Before you start

Work on a cold engine: a hot aluminium head is easily damaged.

Steps

  1. Remove the engine cover, then unplug and pull out the coils one by one, noting their order.
  2. Blow around each plug well so no dirt falls into the cylinder.
  3. Unscrew the plug. If it resists hard, stop: a stripped thread is very expensive.
  4. Thread the new plug in by hand for several turns to avoid cross-threading.
  5. Torque it (often 20 to 28 Nm) and refit the coil.
  6. Do one cylinder at a time, then start and check the engine runs smoothly.

Safety

An over-tightened plug can break or damage the head. Stick to the torque.

Indicative estimate. MecaScan cannot see your vehicle: always have a diagnosis confirmed by a professional, and never work on brakes, steering or airbags without the skills.