How often to change spark plugs depends on the plug type and the engine. As a rough guide, traditional copper plugs were changed about every 20,000 to 30,000 miles, platinum plugs often last around 60,000 miles, and iridium plugs commonly last 60,000 to 100,000 miles or more. Many modern cars come with iridium plugs and a long interval, but your owner’s manual is the authority, and turbocharged or high-performance engines may need shorter intervals.
Typical spark plug change intervals
| Plug type | Typical interval | Notes |
|---|---|---|
| Copper (nickel alloy) | About 20,000 to 30,000 miles | Common in older engines |
| Platinum and double platinum | Around 60,000 miles | Double platinum suits waste-spark systems |
| Iridium | About 60,000 to 100,000+ miles | Original equipment in many modern engines |
These are general ranges; follow the interval in your manual. See iridium vs platinum spark plugs.
When to change them early
- Misfires, rough idle or hesitation; see bad spark plug symptoms and engine misfire
- Harder starting or lower fuel economy
- Oil-fouled or carbon-fouled plugs, which point to another problem to fix
- Higher boost or modified engines, which work plugs harder
Spark plugs and ignition coils
Worn plugs need more voltage to fire, which stresses the coils. Many owners inspect the coil boots when changing plugs and replace any that are cracked or oily. Coils do not need replacing on a schedule; replace them when they fail; see bad ignition coil symptoms and spark plug wires.
Do spark plugs wear out if the car is not driven much?
Plugs wear with use, but age matters too. Plugs left in for many years can seize in aluminum heads, so even on low-mileage cars many owners replace long-life plugs on a time basis as well. Your manual may give both a mileage and a time interval; use whichever comes first.
Cost of waiting too long
Worn plugs make the engine work harder: misfires waste fuel, raise emissions and can overheat the catalytic converter, and the extra voltage they need can shorten coil life. Replacing plugs on time is an inexpensive way to protect the ignition system.
Changing spark plugs
- Work on a cool engine, especially with aluminum heads.
- Blow debris out of the plug wells before removing plugs.
- Check the gap on new plugs against the specification without bending fine-wire tips.
- Thread plugs in by hand, then torque to the specification.
Reading old plugs
Tan or light gray deposits are normal. Black, sooty plugs suggest rich running; oily plugs suggest oil getting into the cylinder; white or blistered plugs suggest overheating or lean running. See engine burning oil.
More guides: outboard spark plugs.
Trouble codes: P0300 Random/Multiple Misfire · P0301 cylinder 1 misfire · all OBD2 codes.
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