Let’s be honest — many drivers never replace their spark plugs, driving well past 120,000 miles. But every once in a while, it’s worth cracking open your owner’s manual to see what your car actually needs.
If you look back far enough, spark plugs used to be replaced only when they completely stopped working. Today, with advances in automotive technology, it’s much easier to know when to replace them — you just need to check your vehicle’s owner’s manual.
For standard spark plugs, the recommended replacement interval is typically between 18,000 and 25,000 miles. However, upgraded iridium spark plugs can last up to 50,000 miles or more, especially if you’re using high-octane fuel and your engine is in good condition.
Common signs of faulty spark plugs include:
Carbon buildup on the tip
Cracks in the ceramic insulator
Corrosion on the side electrode
Improper electrode gap (should be about 0.8 millimeters)
If even one spark plug fails, it’s recommended to replace the entire set. When your engine is running properly, the plugs tend to self-clean.
Consequences of not replacing spark plugs on time:
Engine may fail to start
Catalytic converter damage in vehicles equipped with one
Increased fuel consumption
Rough idling or engine misfires
Burned pistons or damaged gaskets
And that’s just the beginning — almost every component inside the engine can suffer from bad spark plugs.
Other related issues include:
Excessive fuel consumption
Weak air-fuel mixture
High levels of fuel additives
Worn valve stem seals
Malfunctioning valves
Engine knocking or detonation
Worn piston rings
If your engine is running unevenly, the first thing to check is the condition of your spark plugs. Regular maintenance and timely inspections can save you from expensive repairs down the road.