On many four-cylinder engines, changing spark plugs is a beginner-friendly job that takes under an hour. On some V6 and V8 engines, the rear plugs are buried under the intake manifold, and the job becomes much harder. Look at your engine first, then gather the right tools.
Tools and parts
- The correct spark plugs: the exact type listed in your owner’s manual or by the plug maker’s catalog for your engine. Iridium and platinum plugs last much longer than copper ones; do not downgrade.
- A ratchet with extensions and possibly a universal joint for hard-to-reach plugs.
- A spark plug socket of the right size (commonly 5/8 inch or 16 mm on modern engines), ideally with a rubber insert or magnet to hold the plug.
- A torque wrench, because both under- and over-tightening cause problems.
- A gap gauge to check the electrode gap, if your manual specifies one.
- Dielectric grease for the boots of the ignition coils or wires, and anti-seize only if the plug maker recommends it (many modern plugs have a coating and should be installed dry).
- Compressed air or a brush to clean around the plugs before removing them.
Step by step
- Let the engine cool completely. Aluminum cylinder heads are easily damaged when hot.
- Disconnect the battery if your manual recommends it, and remove any engine cover.
- Unplug and remove one ignition coil (or plug wire) at a time, so you do not mix up the firing order.
- Blow away dirt around the plug so nothing falls into the cylinder.
- Unscrew the old plug and look at it; its condition can reveal oil burning, rich running or overheating.
- Check the new plug’s gap if needed, then thread it in by hand to avoid cross-threading.
- Tighten to the specified torque, refit the coil and move to the next cylinder.
When to change them
Intervals vary widely, from about 30,000 miles for copper plugs to 100,000 miles or more for long-life iridium plugs in many modern cars. Symptoms of worn plugs include rough idle, misfires, hesitation, harder starting and higher fuel use; a flashing check-engine light means a serious misfire that should be fixed quickly.
If in doubt
If a plug is seized, or the job requires removing the intake manifold, a mechanic may be the better option; a stripped thread in the cylinder head is an expensive repair. For the number of plugs in larger engines, see how many spark plugs a V8 has, and for other home jobs, basic car maintenance at home.
