What is a spark plug

This is a spark plug.

Don't worry if you have never seen one.

Only petrol engined cars have spark plugs

They sit inside the engine and give a spark that ignites the fuel.

Most cars have 4 spark plugs, one for each cylinder in the engine.

If you drive a V6 you will have 6 spark plugs, and if you
drive  a V8 you will have 8 spark plugs ......etc .. etc.
 

Where are my spark plugs ?

In the engine bay, normally mounted on top or side of the cylinder head.
There will be one ignition lead going to each spark plug.

Here the blue wires are the ignition leads.

Some engines have spark plug covers fitted over the top of them.
These just normally unbolt and lift off so that you can get to the spark plugs.

What do spark plugs do ?

As we briefly mentioned above, they sit inside the cylinder of the engine
and provide a spark to ignite the fuel inside the cylinder (combustion chamber).

We are now getting into the realms of 'how engines work' now and this isn't
what this article is about. So if you want, you can go and read that article.

We will stay here and talk a little more about the spark plugs.
 

Image courtesy of www.britannica.com

Why are spark plugs important ?

If they don't work then the engine won't run, nothing to ignite the fuel.

Spark plugs won't last forever, they can get fouled up with carbon deposits,
they can overheat and not work efficiently.

Symptoms and causes of faulty / worn plugs is discussed more in the article
'How to change your spark plugs'. if you want to take a look.

Check out the video below for more spark plug info ;