New and used spark plugs

When to change spark plugs?

How often spark plugs need to be replaced is dependent on the type of car and spark plug. While conventional spark plugs last less than 50000 miles, iridium and platinum tipped spark plugs can last over 100000 miles.

Failing to replace spark plugs in time can cause misfiring, difficulties starting the engine, slow or inconsistent acceleration and poor fuel economy.

Spark plugs normally cost between £8-25 each (and a 4 cylinder car needs 4 spark plugs, wheres a V6 would require 6).

How to change spark plugs?

Replacing spark plugs is usually quick and easy and does not require much mechanical skills or specialised tools. The following example shows how to replace spark plugs in a Honda Civic, where the 4 cylinder engine is easily accessible under the bonnet. The only tool needed is a ratchet set with a 10 mm socket and a 16 mm spark plug socket.

How to replace spark plugs in a Honda Civic?

Changing spark plugs in a Honda Civic takes around 15 minutes to complete following 8 easy steps:

  1. Ensure the car is turned off and the engine is cool
  2. Unscrew the 10 mm bolt holding the wiring cap
  3. Pull off the spark plug cap
  4. Unscrew the spark plug with a 16 mm socket and extension
  5. Replace the spark plug
  6. Secure the new spark plug in place
  7. Fit the wiring cap back
  8. Repeat for each

Spark plug sockets have a rubber insert that hold onto the spark plug itself to ease removal. Replace spark plugs immediately after each one is removed to avoid contamination. Do not overtighten.

Pull off the spark plug cap
Step #3: Pull off the spark plug cap
Unscrewing the spark plug
Step #4: Unscrew the spark plug

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