A car’s ignition system produces the sparks used to ignite the air/fuel mixture in a petrol engine (diesel engines don’t have an ignition system).
The ignition coil transforms the low voltage electricity from the battery into high-voltage electricity, which is sent along the HT (High Tension) leads to the spark plugs.
The spark plugs are screwed into the cylinder head, and produce sparks inside the combustion chambers.
What does a spark plug do?
Spark plugs are fitted to petrol engines, and their job is to ignite the air/fuel mixture in the cylinders at the correct instant.
When the ignition system sends a voltage down the HT lead to the spark plug, the high voltage causes a spark to jump between the spark plug centre electrode and the earth electrode(s).
The spark ignites the explosive air/fuel mixture, which expands, pushing the piston down the cylinder.
The ‘spark plug gap’ (the gap between the earth electrode(s) and the centre electrode) can be adjusted to suit a particular engine.
The size of the gap is very important, because it controls the way the air/fuel mixture burns. Some spark plugs have more than one earth electrode.
How long do spark plugs last?
Most spark plugs these days should last for 60,000 miles or more. Modern ones are made of ceramic and iridium or platinum, which is more durable material than was used in the past.
That said, you should inspect your spark plugs about every 30,000 miles to make sure they are still in good condition.
If you don’t maintain your spark plugs your engine will cease to run smoothly, and several troublesome issues could develop over time, such as trouble starting your car, misfiring and poor fuel consumption.