At a glance
Regular maintenance level · mixed driving
When
≈ 60,000 km
with mixed driving; your manufacturer's interval comes first
Cost
≈ €95
≈ €43 for a set of plugs alone
EU average, independent workshop, VAT included
DIY difficulty
Moderate
Needs a spark plug socket and a torque wrench, and the ignition coils come off first. Overtightening can damage the engine's thread, and some engines hide the plugs under other parts.
How critical
Medium
Worn plugs rarely leave you stranded, but they waste fuel, and misfires can damage the catalytic converter, which is expensive to replace.
Short answer: Change your spark plugs at your manufacturer's interval, typically every 30,000 to 60,000 km for standard plugs and up to about 100,000 km for long-life platinum or iridium plugs. Track2Drive's default is 60,000 km, about 20% sooner if you drive mostly in town. Only petrol engines have spark plugs: diesels don't. A spark plug change costs about €95 at an independent workshop (EU average).
Every time a cylinder fires, a spark plug lights the fuel. As the plugs wear, the spark gets weaker, and the engine starts harder, uses more fuel and can misfire. A set of plugs costs less than €50; a catalytic converter damaged by misfires costs much more.
What spark plugs do
A petrol engine burns a mix of air and fuel in each cylinder. Something has to light it, thousands of times a minute: that's the spark plug.
- Each cylinder has one spark plug (a few engines have two). A four-cylinder engine has four.
- The ignition coil sitting on top of each plug turns the car's 12 volts into a very high voltage.
- The current jumps across a tiny spark gap between the plug's centre electrode and its earth electrode, and that spark lights the fuel.
- The ceramic insulator keeps the high voltage where it belongs, and the thread screws the plug into the engine.
Diesel engines don't have spark plugs. Their fuel lights by itself when the air is squeezed hard and gets hot. They have glow plugs instead, which only help on cold starts and are a different part.
Why spark plugs wear out
- The electrodes burn away. Every spark removes a tiny bit of metal. Over tens of thousands of kilometres the edges round off and the gap gets wider, so the spark is harder to make and weaker.
- Deposits build up. Soot, oil or fuel additives can coat the tip, and the spark can leak away instead of jumping the gap.
- The rest of the ignition works harder. A wider gap needs more voltage, which strains the ignition coils.
That's why plugs are changed by distance, not when they fail.
Which spark plugs does your car have?
| Type | Typical life | Notes |
|---|---|---|
| Standard (copper core, nickel tip) | About 30,000–50,000 km | Cheapest; common on older engines |
| Platinum | About 60,000–100,000 km | Harder-wearing tip |
| Iridium | About 60,000–100,000 km or more | The hardest-wearing; common on modern and turbo engines |
- Use exactly the plug your manufacturer specifies. The size, the heat range and the gap must match your engine. A "better" plug of the wrong type can run badly or damage the engine.
- Change them as a full set, all the same type and brand.
- Long-life doesn't mean lifetime. Even iridium plugs have a change interval. Your service book has the exact figure for your engine, and some manufacturers also set a time limit in years.
When to change them
Your manufacturer's interval comes first. It depends on the engine and the plug type: anything from about 30,000 km to 100,000 km or more. If you don't know it, use the figures below. They take your maintenance level and your driving into account.
City: Stop-start traffic and short trips mean more starts and more running time per kilometre. The interval is about 20% shorter.
| Level | Replace every | Due soon from |
|---|---|---|
| RegularStandard schedule. Lowest cost, more wear over time. | 48,000 km | 45,000 km |
| CarefulMore often than standard. Longer life, moderate cost. | 32,000 km | 29,000 km |
| EnthusiastMost frequent servicing. Top condition, highest cost. | 24,000 km | 21,000 km |
Mixed: A mix of town and open road. These are the typical figures.
| Level | Replace every | Due soon from |
|---|---|---|
| RegularStandard schedule. Lowest cost, more wear over time. | 60,000 km | 57,000 km |
| CarefulMore often than standard. Longer life, moderate cost. | 40,000 km | 37,000 km |
| EnthusiastMost frequent servicing. Top condition, highest cost. | 30,000 km | 27,000 km |
Highway: Long, steady journeys. The interval stays the same as mixed.
| Level | Replace every | Due soon from |
|---|---|---|
| RegularStandard schedule. Lowest cost, more wear over time. | 60,000 km | 57,000 km |
| CarefulMore often than standard. Longer life, moderate cost. | 40,000 km | 37,000 km |
| EnthusiastMost frequent servicing. Top condition, highest cost. | 30,000 km | 27,000 km |
Track2Drive shows the spark plugs as Due soon about 3,000 km early. If your manufacturer gives a different interval, enter it and Track2Drive will use yours.
Have them changed sooner if you notice the warning signs below.
Warning signs
- The engine is harder to start, especially on cold mornings. (A weak battery causes this too.)
- Rough idling: the car shakes or the engine sounds uneven when standing still.
- Hesitation or jerking when you accelerate.
- Less power than usual.
- Higher fuel use for the same driving.
- The engine warning light comes on.
What happens if you don't change them
- The spark gets weaker. Nothing you notice yet.
- Fuel use goes up and the engine feels less lively.
- Starting gets harder, and the engine idles roughly or hesitates.
- Misfires. A cylinder stops firing now and then, the car jerks, and the engine warning light comes on. The ignition coils are strained and can fail.
- Catalytic converter damage. Unburned fuel from misfires reaches the catalytic converter and can destroy it, an expensive repair.
Why not wait until the engine runs badly?
- The decline is slow. You get used to slightly harder starts and higher fuel use, so you may not notice until misfires start.
- By then other parts suffer. Misfires strain the ignition coils and can damage the catalytic converter.
- Old plugs can be hard to remove. Plugs left in far too long can seize in the engine's thread, making the job longer and riskier.
How spark plugs are changed
- The engine must be cold. Spark plugs are screwed into aluminium, and removing them from a hot engine can damage the thread.
- The engine cover and the ignition coils come off. On some engines, other parts, such as the air intake, have to come off first.
- The area around each plug is cleaned, so no dirt falls into the cylinder.
- The old plugs are unscrewed with a special spark plug socket.
- The new plugs are started by hand, so they can't cross-thread, then tightened to the specified torque with a torque wrench.
- The coils and covers go back on, and the engine is started to check it runs smoothly.
At a workshop this usually takes about 30 to 45 minutes on a four-cylinder engine, longer when other parts have to come off.
At the workshop, ask for
- The exact plug type from your manual
- A full set, not just one plug
- Tightening to the specified torque
- A note on the invoice with the plug type and the mileage
How much a spark plug change costs
A set of plugs for a typical four-cylinder car costs about €43, the same everywhere, and the job takes up to about 45 minutes, so the labour rate makes most of the difference. Figures are estimates for an independent workshop, VAT included.
| Country | Workshop labour rate | Spark plug change |
|---|---|---|
| EU average | €70/h | ≈ €95 |
| Germany | €105/h | ≈ €121 |
| Netherlands | €100/h | ≈ €118 |
| Austria | €95/h | ≈ €114 |
| France | €77.50/h | ≈ €101 |
| Belgium | €69.50/h | ≈ €95 |
| Italy | €65/h | ≈ €91 |
| Spain | €48.50/h | ≈ €79 |
| Poland | €40.50/h | ≈ €73 |
| Portugal | €37/h | ≈ €70 |
Six- and eight-cylinder engines, engines with two plugs per cylinder, and engines where other parts have to come off cost more: up to about €300.
Questions people ask
Do diesel cars have spark plugs?
No. Diesel fuel lights by itself under compression. Diesels have glow plugs, which only help with cold starts and are a different part with a different schedule.
Can I change just one spark plug?
It's better to change the full set, with the same type and brand, so every cylinder fires the same way.
Do iridium plugs last forever?
No. They last much longer than standard plugs, often 60,000 to 100,000 km or more, but they still wear and have a change interval.
Will new spark plugs save fuel?
If the old ones were worn, yes: worn plugs raise fuel use. New plugs won't make a healthy engine use less than it did when new.
Can I change them myself?
If you're comfortable with tools, on many four-cylinder engines it's a manageable job with a spark plug socket and a torque wrench. If the plugs are hard to reach, or you're unsure, leave it to a workshop: a damaged thread in the engine is an expensive mistake.
Do hybrids need spark plug changes?
Yes, petrol hybrids have spark plugs too. Follow your manufacturer's interval. Electric cars have no spark plugs at all.