How often should spark plugs be replaced?

Standard copper plugs: every 30,000 miles. Platinum plugs: every 60,000 miles. Iridium plugs: every 60,000–100,000 miles. Check your owner's manual for the specific interval for your car — many modern cars come with iridium plugs that don't need changing until 100k.

What does a misfiring spark plug feel like?

A rough idle (the engine vibrates or shakes at a stoplight), a stumble when you press the gas, reduced power on hills, and reduced fuel economy. A free OBD2 scan at AutoZone will show codes P0300–P0312 which identify the specific misfiring cylinder.

Can I damage my engine by driving with a bad spark plug?

Yes. An ongoing misfire sends raw, unburned fuel into the exhaust, which can destroy the catalytic converter ($1,500–$2,500 to replace). Fix misfires promptly — a set of plugs costs $20–$80.

Do I have to replace all spark plugs at once?

Yes. If one plug has reached the end of its service life, the others are at the same mileage and equally worn. Replacing all of them at once is the correct approach. Mixing old and new plugs leaves you with uneven combustion.

Spark Plugs

easy DIY~1h job

What it does

Spark plugs are like tiny lightning bolt makers at the top of each cylinder. Your engine mixes air and fuel, then a spark plug fires an electrical spark — exactly like a tiny lightning bolt — to ignite the mixture and push the piston down. Each plug fires thousands of times per minute. Over time, the metal tip that creates the spark erodes, the gap widens, and the spark becomes weak or inconsistent. When a plug misfires (fails to ignite the mixture), that cylinder produces no power and the engine runs rough.

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DIY Cost

~$25

parts only

Shop Cost

~$150

parts + labor

Easy DIY~1h job

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DIY tutorial

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Frequently asked questions

car maintenance — complete guide check engine light — complete guide