Spark Plug Replacement: When and Signs
Written by Muneeb Rana · Last updated 21 October 2026
Quick answer: Spark plug replacement intervals depend on the plug type: traditional copper plugs around every 30,000 miles, and platinum or iridium plugs commonly 60,000-120,000 miles. Signs of worn plugs include rough idle, misfires, hard starting, poor acceleration, lower fuel economy and a check engine light. Your owner's manual lists the exact interval and plug.
TL;DR
- Copper: ~30,000 mi; platinum/iridium: often 60,000-120,000 mi.
- Worn plugs: rough idle, misfires, poor economy.
- Use the exact plug your manual specifies.
Spark plug replacement is a classic tune-up job that most modern cars need only a few times in their life. Here's when it's due and what to watch for.
Intervals by plug type
| Plug type | Typical life |
|---|---|
| Copper / nickel | About 30,000 mi |
| Platinum | Often 60,000-100,000 mi |
| Iridium | Often 60,000-120,000 mi |
See the 30,000, 60,000 and 100,000 mile service checklists.
Signs your spark plugs are worn
- Rough idle or engine shaking.
- Misfires, especially under acceleration.
- Hard starting.
- Sluggish acceleration.
- Worse fuel economy (how to calculate MPG).
- A check engine light, sometimes flashing with a severe misfire. AAA lists worn plugs and ignition coils among common check engine causes.
DIY or shop?
On many four-cylinder engines with plugs on top, it's a manageable DIY job with a spark plug socket and torque wrench. On some V6 and transverse engines, the rear plugs need the intake removed, which is shop work. Always use the plug specified, torque correctly and don't cross-thread aluminium heads.
Log it
Spark plugs are replaced so rarely that people forget when they were done. Log the date, mileage and plug type in CarO's car repair log and check the maintenance schedule tool for when they're next due.
Download CarO free on the App Store or Google Play. Free with ads; optional in-app purchases.
Sources
- AAA: The Check Engine Light, Common Causes and How to Fix It: www.aaa.com (accessed 21 October 2026)
- AAA: Time-Stamped Car Maintenance Checklist: www.aaa.com (accessed 21 October 2026)
- Toyota: Maintenance Schedule (owners): www.toyota.com (accessed 21 October 2026)
Disclaimer: CarO and this website give general car-care information, not professional advice. Maintenance intervals and specifications vary by vehicle, so always follow your owner's manual and a qualified mechanic. Mileage and cost figures are estimates; check local tax rules before using any log for deductions.
FAQ
How often should spark plugs be changed?
Copper plugs about every 30,000 miles; platinum and iridium plugs often 60,000-120,000 miles. Check your manual.
What are the signs of bad spark plugs?
Rough idle, misfires, hard starting, poor acceleration, lower fuel economy and a check engine light.
Can bad spark plugs cause a check engine light?
Yes. Misfires from worn plugs or coils are a common cause.
Should I replace ignition coils with spark plugs?
Not automatically. Replace coils if they're faulty; some owners replace them preventively on high-mileage engines.
Can I upgrade to iridium plugs?
Only if they're the correct heat range and fit for your engine. Using the plug your manual specifies is safest.
Related guides
Track this in CarO
CarO is a free car maintenance tracker app for iPhone and Android that keeps a full service history, reminds you about oil changes and inspections by mileage or date, and logs fuel fill-ups with MPG, odometer readings and car expenses for every vehicle you own. Logs are stored in the cloud and can be exported as CSV.
