Blog / Spark plug replacement

Engine Care · 3 min read

Spark Plugs: When to Replace Them and Why It Matters

Spark plugs are inexpensive individually, but worn ones affect far more than just how the engine feels to drive, which is why they're worth taking seriously rather than leaving until something more obviously breaks.

How often they actually need replacing

This varies significantly by plug type. Standard copper plugs might need replacing every 20,000 to 30,000 miles. Iridium or platinum plugs, now common on newer cars, can last 60,000 to 100,000 miles or more. The handbook gives the manufacturer's specific interval, which is the one to follow, since guessing based on a generic figure can mean replacing them too early or, more commonly, too late.

Signs they're due before the mileage interval

• Rough idling or a noticeable loss of smoothness
• Difficulty starting, particularly in cold or damp weather
• Reduced fuel efficiency for no other obvious reason
• An engine misfire, felt as a slight stumble under acceleration

Why worn plugs cost you more than they save

A worn spark plug creates an inefficient spark, which means the engine burns fuel less completely. That shows up as worse fuel economy and, over time, can contribute to carbon build-up elsewhere in the engine and exhaust system. The cost of delaying a routine plug change tends to show up as a larger fuel bill long before it shows up as anything else.

Not a DIY job to skip carefully

Spark plugs are one of the more accessible maintenance items for confident DIYers, but getting the torque and gap right matters, since over-tightening or an incorrect gap can cause new problems rather than fixing the old one.