It’s amazing how such a simple and small component can play such a huge part in your vehicle’s performance, but without a set of functioning spark plugs, you aren’t going anywhere. Of course, as with many of your car’s consumable components, your spark plugs will wear out over time. How long that period is, is down to the plug and the type of driving you carry out each day.

This article looks at the most common symptoms of dirty or damaged spark plugs or those that have arrived at the end of their working life.

How long do spark plugs last?

The life of a spark plug depends on the type of plug and your driving style and conditions. Spark plugs are manufactured using different materials, each offering a recommended lifespan; as you can imagine, the longer the lifespan, the higher the price.

  • Copper spark plugs: 20–30k miles
  • Platinum spark plugs: 50–60k miles
  • Iridium spark plugs: 80–100k miles

What does spark plug wear look like?

Removing your spark plugs isn’t much of a job for a competent DIY mechanic, so a visual inspection is a great place to start if you think there’s a problem with your plugs.

Delivering millions of sparks and ignitions over each plug’s lifetime results in minute levels of wear to the electrodes, resulting in the gap between them widening. It’s highly unlikely you’ll be able to spot that by eye but what you may notice is excess build-up or destructive wear on either or both electrodes.

If you find a shiny black oily residue, then oil could be finding its way into the system. That’s not all that could be getting through, though; it’s quite possible to find oil, fuel or coolant contaminating spark plugs. If coolant is seeping in and not oil, the residue on the plugs is likely to be white and chalky.

Carbon fouling occurs when the plugs don’t create enough heat to burn away the build-up that occurs with ignition or the fuel mix is too rich. Carbon fouling results in a grey or black sooty looking appearance.

The most common signs that you need new spark plugs

The check engine light illuminates on your dashboard

It sounds so simple, but modern cars are built to detect issues, preventing them from getting out of hand and developing into more severe avoidable problems. If the check engine light illuminates, it could be down to your spark plugs. Admittedly, the check engine light appears for all sorts of engine issues, so it isn’t guaranteed to be the spark plugs; it’s just a good place for a first inspection if you haven’t got diagnostic tools to hand.

Misfiring engine

Misfiring is a sure sign that there’s something amiss with your ignition system. It could be anything from the coils, fuel mix, electrical supply, and of course, it could be your spark plugs. So if you feel the car shake or judder, experience loss of power or poor performance, check your plugs. A misfiring engine will affect your fuel economy, increase emissions, and could lead to more severe and expensive damage to associated components.

Poor fuel economy

Car engines are incredibly efficient, but when they’re not working to the precise tolerances they’re designed to, fuel gets wasted and even more is used, working harder to deliver the same performance.

It’s worth checking your plugs if you notice you’re filling up more regularly yet covering the same mileage. Erratic engine firing can affect your mileage more than you’d expect.

Starting problems

Most drivers will jump straight to the conclusion that it’s a battery issue if they’re having trouble starting their car. However, the electrical charge delivery is only one part of a range of systems working on getting your car started, and while it could well be the culprit, it doesn’t have to be. Dirty, damaged or worn spark plugs can cause just as many problems getting your engine running as the other components they work with.