DIY guide · Moderate
How to change your spark plugs
New plugs fix rough idle, hard starts and misfires. The risk is dropping something into a cylinder or cross-threading a plug, so go slowly and keep everything clean.
- Difficulty
- Moderate
- Time in the bay
- 1.5 to 3 hours
- Best bay
- Floor bay
- Bay cost, plus tax
- $40 to $60
This is a general guide, not a manual for your car. Your vehicle's service manual comes first, especially for torque values, fluid types and capacities. Support the car on the lift locks or jack stands before you go under it, wear eye protection, and if a step feels wrong, stop and ask us. We do not do welding, grinding or painting in the bays.
Look these up before you book
- Plug type and gap
- Plug torque
- Whether plugs sit under the intake manifold on the rear bank
Tools
- Spark plug socket with a rubber insert
- Extensions and a swivel
- Torque wrench
- Plug gap tool
- Compressed air
- Dielectric grease
- Ratchet and screwdrivers for covers and coils
Parts and fluids
- Spark plugs, the exact type for your engine
- Ignition coil or boot only if you find a bad one
- Anti-seize only if your plug maker allows it
There is an AutoZone nearby, and during business hours parts usually reach the shop in about 10 to 20 minutes. Forgot a filter or need a different size? Order it, keep working, and do not lose your slot.
The retailer's own vehicle picker confirms what fits your car. Always compare the part number with your old part.
Step by step
- Work on a cold engineAluminum heads can strip if you pull plugs hot.
- Remove covers and coilsLabel wires or coils so each goes back where it came from. Disconnect the battery if you want extra safety.
- Blow out the wellsUse compressed air so dirt does not fall into the cylinder when the plug comes out.
- Unscrew one plug at a timeGo slowly and keep it straight. Check the old plug: its tip colour shows how the cylinder is running.
- Check the gap on the new plugMany plugs come pre-gapped. Check, but do not squeeze or bend the electrode hard.
- Thread by hand, then torqueStart it by hand so you feel it catch, then torque to spec. A little dielectric grease inside the boot helps.
- Refit the coils, covers and connectorsMake sure each coil clicks home, then start the engine and listen.
Mistakes to avoid
- Cross-threading a plug because it was started with a ratchet
- Over-tightening and cracking the plug or the head
- Mixing up coil positions
- Using the wrong plug because the part number came from a guess
Stop and ask for help if
- If a plug is seized, or a plug socket is stuck in the head, do not force it. Ask us first.
- If the engine misfires after new plugs, a coil, injector or compression problem may be the cause.
Doing it in our bays
You do not need a lift for most engines, so the floor bay costs less. If the plugs are under the intake manifold, ask about a lift for comfort and access.
Every bay has air, power, work lights and jack stands, and the lift bays come with a short safety walkthrough. Bring your own hand tools, parts and fluids. New to lifts? Read how your first visit goes.
Questions
How often should plugs be changed?
Many modern plugs last 60,000 to 100,000 miles. Follow your owner's manual.
Do I need anti-seize?
Only if the plug maker says so. Many modern plugs have a plated finish and should be installed dry.