Many modern iridium or platinum spark plugs are rated for roughly 60,000 to 100,000 miles, while older copper plugs need replacing much sooner. Check your owner's manual. Worn plugs cause hard starts, rough idle, lower fuel economy and misfires, and they make ignition coils work harder, which can lead to coil failures.
Typical intervals
| Plug type | Common interval |
|---|---|
| Copper / nickel | About 20,000–40,000 miles |
| Platinum | About 60,000–100,000 miles |
| Iridium | About 60,000–120,000 miles |
Your owner's manual is the authority. Turbocharged and direct-injection engines can be harder on plugs, and severe-duty use shortens intervals.
Signs your plugs are worn
- Rough idle or a slight shake at stops
- Hard starting
- Hesitation when accelerating
- Lower fuel economy
- Misfire codes (P0300–P0308) and a check engine light
- A flashing check engine light under load
Why worn plugs cost more than plugs
As the electrode wears, the gap grows. A wider gap needs more voltage to spark, and the ignition coil has to work harder to supply it. Over time, that extra stress can cause coils to fail, which is why worn plugs and failed coils often show up together.
If misfires go on long enough, unburned fuel can overheat the catalytic converter. That's how a modest maintenance item becomes an expensive repair. See P0300 misfire codes.
What a plug can tell a mechanic
| Plug appearance | What it suggests |
|---|---|
| Light tan or gray deposits | Normal |
| Black, dry soot | Rich running, weak spark, lots of idling |
| Wet, oily | Oil getting into the cylinder |
| White, blistered | Running hot or lean |
| Cracked insulator | Plug damage, can cause misfire |
Things to know about replacement
- On many V6 engines, the rear plugs are buried under the intake plenum, which makes the job take longer.
- Plugs should be torqued to spec. Too loose or too tight can cause problems, especially in aluminum heads.
- Oil in the plug wells usually means a valve cover or tube seal leak. Fix it, because oil damages coils.
Frequently asked questions
Do I need to replace all the spark plugs at once?
Yes. Plugs are replaced as a set so they wear evenly.
Should I replace ignition coils with the plugs?
Not automatically. Replace coils that test bad. On high-mileage engines, it's worth discussing.
Can I drive with a bad spark plug?
Briefly, but misfires stress other parts. If the check engine light flashes, stop driving.
Do you replace spark plugs at my home?
Yes. Spark plug replacement is a routine mobile job on most engines.
Want a mechanic to confirm it?
We come to you in Lexington, Irmo, Chapin, Cayce, West Columbia and Columbia, and we test before we replace anything.
