Knowledge base
Replacing spark plugs — when, why and how many?
A spark plug makes the spark that ignites the mix of air and petrol in the cylinder. It does that thousands of times a minute. Over time the plug wears and the spark gets weaker. You don't notice it all at once but gradually: the engine runs less smoothly and uses more fuel.
What a spark plug does and why it wears
Every spark burns away a tiny bit of material from the electrodes. The gap between the electrodes grows and the ignition coil needs more voltage to make the spark jump. Deposits from combustion add to that. At some point the spark is no longer strong enough every time — especially on a cold start, under load or in damp weather.
Spark plugs are only found in petrol engines, including hybrids with a petrol engine. A diesel has no spark plugs but glow plugs. These only help with cold starts and have no fixed replacement interval.
Signs of worn spark plugs
- Hesitation or jerking when accelerating, especially under load. Often that is a cylinder misfiring.
- Rough idle: the engine shakes more than you are used to.
- Harder starting, especially when it is cold or damp.
- Higher fuel use and less pulling power: petrol that doesn't burn properly gives no power.
- Engine warning light on or flashing. Flashing often points to a serious misfire. Drive gently and have it checked soon: unburnt petrol can damage the catalytic converter.
The same symptoms can also come from an ignition coil, an injector or an air leak. That is why it makes sense to read the fault codes first. Then you see which cylinder misfires and whether the plug really is the cause.
How often: nickel, platinum or iridium
The interval is in your car's service schedule, in kilometres and in years. It depends mainly on the type of plug:
- Nickel (standard) wears fastest, so the interval is often shorter.
- Platinum and iridium have harder electrodes that wear more slowly. Manufacturers often state 60,000 km or more for these, plus a maximum number of years.
Turbo engines with direct injection load the plugs harder. There the interval is often shorter than on a similar engine without a turbo. If you drive little, watch the years: even a plug with low mileage can seize in the cylinder head after a long time.
Always use the type specified for your engine. A “better” plug of another type or with a different heat range brings no gain and can even cause problems.
How many plugs and what the calculator shows
The number of spark plugs equals the number of cylinders: a three-cylinder has three, a four-cylinder four. They are always replaced as a set, so every cylinder gets the same spark.
Enter your number plate in the service calculator and you see which spark plugs belong to your engine, with part number and an indicative price per plug. Labour is shown as a separate line. All prices are an indication including VAT. If the final price differs by more than 10 %, we call you first.
Frequently asked questions
Can I keep driving with worn spark plugs?
For a while, yes, but the engine uses more fuel and a misfiring cylinder can damage the catalytic converter. If the engine warning light flashes, drive gently and have it checked soon.
Does my diesel have spark plugs too?
No. A diesel has glow plugs for cold starts. These are usually only replaced when they fail. That is why the calculator only shows spark plugs for petrol engines.
Should all spark plugs be replaced at the same time?
Yes, as a set. Every cylinder then gets the same spark, and covers or other parts don't have to come off twice.
How do I know which interval applies to my car?
It is in the service book or in the digital service history. Not sure? Send us your number plate via WhatsApp and we will look it up for you.
See which spark plugs fit your engine, with part number and price per plug, in the service calculator or read more about car servicing in Tilburg.