Spark plugs may be small, but they play a huge role in keeping your engine running smoothly. They ignite the fuel-air mixture that powers every piston stroke, and without them, your car simply won’t move. But because they’re tucked away and usually out of sight, most drivers don’t think about them until the car starts misfiring. So, how often should you really change spark plugs? Mechanics have a few clear guidelines, and it depends on what’s under your hood.
The Old Rule of Thumb
For decades, mechanics advised replacing spark plugs every 30,000 miles. That made sense when plugs were made with copper cores, which wear down faster. On older cars from the 80s and 90s, sticking to that schedule prevented hard starts and kept engines running efficiently. If you’re driving a classic or an older beater, this old-school interval still applies.
Modern Spark Plug Technology
Today’s cars often use platinum or iridium spark plugs, which are built to last far longer. Mechanics say these advanced plugs can go 60,000 to 100,000 miles before they need attention. Some automakers even advertise “lifetime” plugs, though most professionals recommend taking that claim with a grain of salt. Heat, fuel quality, and engine design all affect lifespan, so relying solely on the marketing pitch can be risky.
Signs Your Spark Plugs Need Replacing
You don’t always need a calendar reminder to know when plugs are due. Mechanics point to a few clear warning signs: rough idling, sluggish acceleration, poor fuel economy, and hard starts. In some cases, a misfiring cylinder will even trigger the check engine light. If your car starts feeling “off” and you haven’t changed plugs in years, it’s worth pulling them out for a look.
What Mechanics Recommend
Most mechanics suggest following your car’s maintenance schedule, but they add a dose of real-world advice. If your car has copper plugs, stick with the 30,000-mile interval. For platinum or iridium, aim for somewhere between 60,000 and 90,000 miles, even if the manufacturer claims longer. It’s also smart to replace them sooner if you drive mostly in stop-and-go traffic or tow heavy loads, since engines in those conditions put more stress on plugs.
The Cost Factor
The good news is that spark plugs themselves are relatively cheap. Copper plugs often cost just a few bucks apiece, while iridium plugs might run $10–$20 each. Labor is what makes the difference. On some cars, like a Toyota Corolla, replacing plugs is a quick 30-minute job. On others — say a V6 buried under intake manifolds — the same job can take several hours. That’s why mechanics say it’s smart to budget for labor as much as parts.
DIY or Leave It to the Pros?
For handy drivers, spark plug replacement is one of the more approachable DIY jobs. With a socket set, a torque wrench, and a bit of patience, you can often save money doing it yourself. But some engines make the job nearly impossible without specialized tools. Mechanics warn that overtightening or cross-threading a plug can lead to expensive cylinder head repairs, so if access is tight or you’re unsure, it may be worth paying a pro.
The Bottom Line
Spark plugs might last longer than they used to, but they’re not immortal. Mechanics agree that keeping up with replacement intervals saves money in the long run by preventing poor fuel economy, rough running, or even catalytic converter damage from misfires. Whether you stick to the factory schedule or go by your mechanic’s cautious recommendation, don’t ignore these little parts — your engine depends on them more than you think.
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