Changing spark plugs yourself: sensible saving or false economy?
This one splits right down the middle. A garage charges £70 to £160 to change spark plugs, while the plugs themselves cost £15 to £40. On an older petrol car with the plugs sitting in plain view, it's a genuinely easy Saturday job and the saving is real. On a modern engine with coil packs buried under plastic covers and plugs at the bottom of deep wells in an alloy head, one slip with the tightening can cost you more than ten garage visits. Know which car you have before you decide.
What you'd pay a garage, and what the parts cost
| Option | Cost |
|---|---|
| Garage spark plug change | £70–£160 |
| Plugs only (set of 4, DIY) | £15–£40 |
| You save by DIY | £50–£130 |
The spread in the garage price is mostly about access. Four plugs sitting on top of an old Fiesta engine take twenty minutes. Six plugs on a V6 where the back three hide under the intake can take two hours, and you'll pay for every one of them. The saving from DIY is bigger here than on an oil change, which is exactly why it's worth an honest look at whether your car is the easy kind or the risky kind.
Honestly, how difficult is it?
Two different jobs wearing the same name. On older petrol engines, roughly pre-2005, you pull a rubber lead off each plug, unscrew it with a plug socket, screw the new one in, done. If that's your car, do it yourself and pocket the difference. Buy a proper magnetic spark plug socket set, because an ordinary socket lets the plug drop into the engine bay and that gets old fast.
Modern engines are a different story. The plugs live at the bottom of deep, narrow tubes in the cylinder head, each one capped by a coil pack, the little ignition unit that replaced the old distributor and leads. The coil pack connectors go brittle with heat and snap if you're clumsy, at £25 to £60 a coil. The head itself is aluminium, which is soft. Overtighten a plug into an alloy head and you can strip the thread, and repairing a stripped plug thread means a helicoil insert or, worst case, head removal. That's a three-figure mistake on a good day and a four-figure one on a bad day.
Gapping trips people up too. The gap is the tiny distance the spark jumps across at the plug tip. Most modern plugs come pre-gapped and shouldn't be touched, especially iridium ones where the fine electrode snaps if you lean on it. Fit the exact plug the handbook lists and leave the gap alone unless the box says otherwise.
The cars where you should leave it to a garage
Be honest with yourself here. Give it a miss if the plugs are down deep wells and you've never done one before. If any plug feels seized when you crack it loose, stop, because forcing a seized plug out of an alloy head cold is how threads die. If your engine is turbocharged and direct injection, the plug spec and torque matter more, not less. And if removing half the intake is needed just to see the plugs, the garage's £160 stops looking like much money.
A torque wrench isn't optional on a modern engine. Plugs have a specified tightness, usually around 20 to 25 Nm, and "about that tight" by feel is precisely how the horror stories start.
Paying a garage: what's a fair deal?
£70 to £160 fitted at an independent, plugs included, with awkward engines at the top end. Main dealers often want double, and for a plug change there's no good reason to pay it; see our dealer vs independent comparison for why. One tip: plugs are often due at a major service anyway, so ask for them to be done then. The labour overlaps and a fair garage will charge you less than the standalone price.
Common questions
How much does it cost to replace spark plugs in the UK?
A fair independent garage charges £70 to £160 including plugs for most four-cylinder cars. Engines with awkward access or six cylinders cost more. The plugs alone are £15 to £40 a set, so DIY saves £50 to £130 if your engine is the easy type.
How often do spark plugs need changing?
Anywhere from 30,000 to 60,000 miles depending on the plug type and engine, and some long-life iridium plugs stretch to 100,000. Your service schedule states the interval. Misfires, rough idle or poor starting before then can point to a failing plug or coil pack.
Can I damage my engine changing spark plugs?
Yes, and it's the main argument for caution. Overtightening strips threads in the aluminium cylinder head, dirt falling down the plug well ends up inside the cylinder, and brittle coil pack connectors snap. On an older engine with easy access the risks shrink to nearly nothing.
Do new spark plugs need gapping?
Usually not any more. Most modern plugs arrive pre-gapped for your engine, and iridium or platinum plugs shouldn't be adjusted at all because the fine electrodes are fragile. Only gap a plug if the packaging or your handbook specifically tells you to, using a proper gapping tool.
Are expensive iridium spark plugs worth it?
If your car came with iridium plugs from the factory, fit iridium again; the long service interval assumes them. If it came on basic copper plugs, expensive plugs won't add power, they just last longer. Fitting the exact type your handbook lists always beats upgrading.