Spark plug replacement: cost, interval, and signs
A spark plug replacement usually costs about $100 to $250 for a four-cylinder engine at a shop, according to AAA, and more for a V6 or V8. Consumer Reports puts the usual interval at around 100,000 miles, which fits long-life iridium or platinum plugs, but the interval in your owner’s manual is the one to follow. Rough idle, misfires, hard starts, and lower MPG are the common signs of worn plugs.
On this page (8 sections)
The short answer
| Question | Answer |
|---|---|
| Cost | About $100–$250 for a four-cylinder, $150–$350 for a V6, $200–$500 or more for a V8 (AAA); Consumer Reports: $200–$500 |
| Interval | Around 100,000 miles for many modern cars (Consumer Reports); copper plugs much sooner. Your manual decides |
| Signs | Rough idle, misfires, hard starting, hesitation, lower MPG, check engine light |
| Do it yourself? | On some four-cylinder engines; many V6 engines need parts removed to reach the rear plugs |
How much a spark plug replacement costs
AAA puts a typical spark plug replacement at $100 to $250, and says it can go past $500 for larger engines or dealer work. Consumer Reports gives $200 to $500. The difference is mostly the engine:
| Engine | Typical cost |
|---|---|
| Four-cylinder | $100–$250 |
| V6 | $150–$350 |
| V8 | $200–$500 or more |
From AAA. Prices vary by labor rate, plug type, and how hard the plugs are to reach. Get a written estimate for your engine.
What moves the price:
- Number of cylinders. One plug per cylinder on most engines, so a V8 takes twice as many as a four-cylinder.
- Access. On many V6 engines the rear plugs sit under the intake manifold, which has to come off. Consumer Reports notes that some cars need panels removed to reach the plugs.
- Plug type. AAA lists copper plugs at about $2–$5 each and iridium at about $12–$25 each. Use the type your manual specifies.
- Ignition coils or wires. If a coil or plug wire has failed, it adds parts.
How long spark plugs last
It depends on the plug material. Consumer Reports gives around 100,000 miles as the usual interval; that fits the long-life iridium and platinum plugs. AAA’s figures by type:
| Plug type | Typical life |
|---|---|
| Copper (nickel) | 20,000–30,000 miles |
| Single platinum | Up to 60,000 miles |
| Double platinum | 60,000–100,000 miles |
| Single iridium | Up to 100,000 miles |
| Double iridium | Up to 120,000 miles |
From AAA. Your owner’s manual gives the interval and the plug type for your engine; follow it over any chart.
Don’t swap to a cheaper type than the manual calls for. Champion, a spark plug maker, warns that putting copper or platinum plugs in an engine designed for iridium can hurt performance, and copper plugs need changing about every 20,000 miles.
Signs of bad spark plugs
AAA lists these signs that spark plugs are worn or fouled:
- Hard starting, especially in cold weather
- Rough idle or a shaking engine at a stop
- Misfires, which can turn on the check engine light
- Hesitation or sluggish acceleration
- Lower gas mileage
- Rattling or popping noises from the engine
A flashing check engine light usually means a severe misfire. Slow down and have the car checked soon, because unburned fuel can overheat and damage the catalytic converter. Worn plugs are only one cause of these signs; a failing ignition coil, a vacuum leak, or a dirty air filter can do the same, so ask for a diagnosis before the shop replaces parts.
Replace them yourself or at a shop?
On many four-cylinder engines, the plugs sit on top under the ignition coils, and the job takes basic tools, a spark plug socket, and a torque wrench. Do it only on a cold engine, change one plug at a time, check the gap if the plug isn’t pre-gapped for your engine, and tighten to the torque in the service information. Cross-threading a plug in an aluminum cylinder head is a costly mistake. On engines where the intake has to come off, a shop is usually the better choice.
What to write in your maintenance log
- Date and odometer reading
- Plug brand, type, and part number, and the gap
- Any coils or wires replaced
- The shop and the cost
- The next due mileage from your owner’s manual
At 100,000 miles between changes, few owners remember the last one. Write it in a free car maintenance log and keep the receipt with your car maintenance records.
FAQ
How much does it cost to replace spark plugs?
About $100 to $250 for a four-cylinder engine, $150 to $350 for a V6, and $200 to $500 or more for a V8, according to AAA. Engines where the intake has to come off cost more.
How often should you replace spark plugs?
At the interval in your owner’s manual. On many modern cars with iridium or platinum plugs, that is around 100,000 miles; copper plugs need changing much sooner.
What happens if you don’t change your spark plugs?
Worn plugs make the engine misfire, start hard, and use more gas. Ongoing misfires can damage the catalytic converter, which costs far more than a set of plugs.
Should I replace ignition coils with the spark plugs?
Only if a coil is failing or the shop finds a problem. Coils don’t have a set replacement interval on most cars. Ask the shop to show you the misfire code or test result.
Sources
- AAA, What is the average spark plug replacement cost? (costs by engine, part prices and life by plug type, signs; checked November 12, 2026): aaa.com
- Consumer Reports, Consumer Reports’ guide to car maintenance (spark plugs: around 100,000 miles, $200–$500; updated May 6, 2026): consumerreports.org
- Consumer Reports, The cars and SUVs with the highest repair costs for common fixes (hard-to-reach spark plugs): consumerreports.org
- Champion, Spark plug materials (copper about 20,000 miles; use the type in the owner’s manual): championautoparts.com