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How to change spark plugs

Ellie Dyer-Brown, 1 year ago

3 min read

  • Advice
  • Maintenance
  • howto
Spark Plug

WhoCanFixMyCar looks at the different types of spark plugs that are available and how to replace them at home


What are spark plugs?

How to change spark plugs

What spark plugs for my car?

Five symptoms of bad spark plugs

Spark plug tester

Frequently asked questions

What are spark plugs?

Spark plugs ignite the air-fuel mixture in the combustion chamber of petrol engines, providing the main source of power. Fortunately, they're relatively cheap to buy and can be changed at home with a small amount of know-how.

Spark plugs help your engine to start and run smoothly; when they go wrong, you might notice your engine misfiring and your car might even fail to start. When this happens, it's time for a replacement.

How to change spark plugs

  • Make sure the engine is cool and clean the area around the spark plugs

  • Optionally, you can disconnect the negative terminal of the battery for safety purposes

  • Remove the first spark plug by pulling the wire plug as close to the base as you can

  • Never yank the wire; fit your socket wrench and extension bar to slowly remove the plug if you can't do this by hand

  • Measure the gap of the spark plug. The ideal gap measurement will be specified in your owner's manual

  • Clean around the threads using a wire brush or compressed air

  • Use anti-seize lubricant on the threads

  • Turn the new plug backwards on the thread until you have located the hole and positioned it correctly

  • Put the spark plug wire boot back on the spark plug (push until it snaps on)

Looking under car hood image

Changing spark plugs is something you can do at home, but if you don’t feel confident working under the bonnet yourself, there are plenty of expert mechanics on WhoCanFixMyCar who can help.

What spark plugs for my car?

There are a few different types of spark plugs out there; choosing the right ones for your car is of paramount importance. 

Many websites allow you to enter your registration plate and will then tell you the specific spark plugs you need. You can also find this information in your owner’s manual.

Copper/nickel spark plugs

Many spark plugs contain copper or nickel in their centre because these are excellent metals for conducting electricity. However, the lifespan of these spark plugs is relatively short compared to some others that are available.

Single platinum spark plugs

Platinum-tipped spark plugs are slightly more pricey than some of their counterparts, but they have a much longer lifespan. Platinum doesn't erode in the same way that nickel does so it is well-suited to modern car engines.

Double platinum spark plugs

These spark plugs certainly aren't budget friendly, but they do offer enhanced performance - even more so than single platinum spark plugs.

Iridium spark plugs

Iridium is the most resistant to corrosion of all the metals listed above. It can withstand temperatures of up to 2,000 degrees. Spark plugs of this kind have a fine-wire centre that is better able to conduct electricity, and they can sometimes last as long as platinum spark plugs.

Silver spark plugs

Silver spark plugs create sparks of increased energy compared to many other types available on the market, and they also have the best thermal conductivity. Typically, they are fitted on older, European high-performance cars and occasionally motorcycles.

Five symptoms of bad spark plugs

  • Misfiring engine - this will cause your engine to lose power momentarily before regaining speed. You might also notice a loud popping sound and black smoke.

  • Trouble starting - without functioning spark plugs your engine won't be able to start.

  • Slow acceleration - this is a common symptom when there's a fault with the ignition system.

  • Poor fuel economy - faulty spark plugs significantly impact fuel consumption.

  • Black exhaust smoke - unusual smoke usually accompanies engine misfires.

Spark plug tester

There are many different spark plug testers available to buy online. They are affordable and safe to use - here's how.

  • Remove the high tension (HT) lead and plug the device in-line. It should be connected to the end of the HT lead and the base of the spark plug

  • Start the engine as you normally would. If the device lights up, this indicates that there is a strong electrical input; if it doesn't light up, the spark plug likely needs replacing.

You can do this yourself or use WhoCanFixMyCar to find a reliable local garage to do it for you.

Frequently asked questions

How long do spark plugs last?

It's a good idea to change your spark plugs regularly to ensure your engine can continue to function as normal. Generally, they last around 20,000 to 30,000 miles.

During a full service worn spark plugs will also be replaced. Find out the difference between a full service and an interim service here.

Do diesels have spark plugs?

Diesel engines work differently to petrol engines; for that reason, they have glow plugs rather than spark plugs.

Is there a spark plug removal tool?

Yes, you can purchase tools which are designed to make it easier to remove spark plugs. For example, spark plug spanners come in different sizes and are designed to fit into spark plug sockets.

What can I use as a spark plug cleaner?

If you're willing to spend a little extra cash, there are spark plug cleaning machines which plug into the air hose. This isn't necessary, however - instead, you can purchase cleaner spray for spark plugs for under £20.

What is an ignition spark plug?

An ignition spark plug is the same as a regular spark plug - sometimes they are also simply referred to as plugs.

How does a spark plug work on an electric car?

Electric cars don't require spark plugs because they are battery powered.

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