The short answer
It depends on the plug type. Copper plugs last 20,000 to 30,000 miles, platinum about 60,000, and iridium — used in most modern engines — 80,000 to 100,000 miles. Always follow your owner's manual. A full replacement typically costs $100 to $500 on a four-cylinder, and up to $700 on hard-to-reach V8s.
How often should spark plugs be replaced by type?
The interval depends on the plug material. Copper plugs last 20,000 to 30,000 miles, platinum plugs about 60,000, and iridium plugs 80,000 to 100,000 — and most modern vehicles ship with iridium from the factory. Always confirm against your owner's manual, since the manufacturer's schedule overrides any generic range.
| Plug type | Replacement interval | Cost per plug |
|---|---|---|
| Copper | 20,000–30,000 mi | $2–$10 |
| Platinum | ~60,000 mi | $10–$20 |
| Iridium | 80,000–100,000 mi | $15–$30 |
A replacement guide from Kelley Blue Book notes that iridium and platinum plugs have made long service intervals the norm on newer cars.
What are the signs spark plugs need replacing?
Worn plugs make the engine misfire, idle roughly, and start hard, and they can cut fuel economy as combustion becomes less efficient. A check engine light, hesitation when accelerating, and an unusual increase in fuel use are common warnings. Symptoms usually build gradually rather than failing all at once.
- Rough or shaky idle and hard starting.
- Engine misfires or hesitation under acceleration.
- Noticeably worse fuel economy.
- A check engine light, often a misfire code.
If the light is on, our guide to what the check engine light means explains how to read the code before you replace parts.
How much does it cost to replace spark plugs?
A full replacement typically runs $100 to $500 on a four-cylinder engine, and up to $700 or more on V8s where the plugs sit behind the intake or under coil packs. The plugs themselves are cheap — most of the cost is labor, which climbs with how hard the plugs are to reach.
- Four-cylinder: roughly $100–$500 for parts and labor.
- V6 / V8 with difficult access: up to $700+.
- Parts only: often $2–$30 per plug depending on material.
Estimates vary by region and vehicle; RepairPal publishes ranges you can compare against a shop's quote.
Can you replace spark plugs yourself?
On many four-cylinder engines, yes. You need a spark plug socket, a gap gauge, and a torque wrench to avoid over-tightening, which can crack the plug or strip threads. V6 and V8 engines with plugs behind the intake manifold or under coil packs are far harder, which is what pushes professional jobs toward the high end.
- Let the engine cool fully before starting.
- Remove one coil or wire at a time so cylinders don't get mixed up.
- Check the gap on new plugs if not pre-gapped.
- Torque each plug to the manufacturer's specification.
Spark plugs are one of several routine items — keep the rest current with our oil change schedule.
Frequently asked questions
What are the signs that spark plugs need replacing?
Watch for rough idling, hard starting, engine misfires, hesitation under acceleration, reduced fuel economy, and a check engine light. Worn plugs make the engine work harder and burn fuel less efficiently, so symptoms often build up gradually before a clear failure.
Can bad spark plugs cause a check engine light?
Yes. Worn or fouled plugs cause misfires that the engine computer detects, commonly triggering codes in the P0300 range. Spark plugs are among the most frequent causes of check engine lights, so a scan tool that points to misfires often traces back to the plugs or coils.
Is it worth upgrading to iridium spark plugs?
Usually only if your engine specifies them. Iridium plugs last 80,000 to 100,000 miles versus 20,000 to 30,000 for copper, so they cut how often you service them. But fitting iridium in an engine designed for copper rarely adds power, so match the manufacturer's spec.
Can I replace spark plugs myself?
On many four-cylinder engines, yes — it needs a spark plug socket, a gap tool, and a torque wrench, plus care not to over-tighten. V6 and V8 engines with plugs behind the intake or under coils are harder, which is why pro jobs can run $100 to $700.
Sources
CarsLens is editorial guidance, not individualized advice. This page draws on Kelley Blue Book and RepairPal.