📋 Recommended Interval
Miles
30,000–100,000 miles
Time
5 years
DIY Cost
$15–$60
Shop Cost
$100–$400
Use whichever comes first, miles or time. Severe service (short trips, towing, dust, extreme heat or cold) shortens the safe interval by 25–50%.
🧠 Why This Interval Matters
Worn plugs cause incomplete combustion, which strains coils, dumps unburned fuel into the catalytic converter, and triggers misfire codes. Replacing plugs is cheap, replacing a catalytic converter from prolonged misfires is $800–$2,000.
⚠ Signs You're Overdue
- Rough idle or stumbling under load
- Misfire (P0300 or P03xx codes)
- MPG dropped noticeably
- Hard cold starts
- Plug gap is wide or electrode is rounded when removed
What happens if you skip itMedium. Direct-injection turbo engines are especially sensitive, worn plugs can pre-ignite and crack ringlands within weeks.
💵 DIY vs Shop Cost
DIY
$15–$60
Shop
$100–$400
Difficulty
Easy to Moderate
Shop pricing varies by region and vehicle. Independent shops are typically 25–40% cheaper than dealerships for the same work. DIY assumes you have basic hand tools.
🛒 Related Items & Typical Life
| Item | Typical Life | Replace Cost |
|---|---|---|
| Spark plug set (4–8 plugs) | Per interval | $15–$60 |
| Anti-seize and dielectric grease | Every install | $5–$10 |
| Ignition coils (if failing) | As needed | $30–$80 each |
🔗 Related Guides
❓ Frequently Asked Questions
How do I know if my plugs are iridium?
Check the part number on the box or the existing plug. Iridium plugs have an extremely thin center electrode (~0.5mm). The owner's manual lists the OEM spec.
Do I need to gap pre-gapped plugs?
Always check with a feeler gauge. Pre-gapped doesn't mean correctly gapped, and shipping can deform the electrode.
What about coils, replace at the same time?
If a coil fails, replace it. Replacing all coils preventively is overkill unless mileage is very high (150,000+) or you're seeing repeat misfires.
Can I use upgraded plugs?
Stick with the OEM heat range. Hotter or colder plugs can foul or pre-ignite. Iridium upgrades from copper are fine and last longer.
How tight should plugs be?
Use the torque spec in the manual (typically 15–25 ft-lb). Overtightening cracks the porcelain or strips aluminum heads.
Do plugs really last 100,000 miles?
Iridium can, but performance degrades the last 20,000. Replacing at 80,000 keeps the engine running its best.