Spark Plugs have four main functions:

It fills a hole in the cylinder head.
It acts as a dielectric insulator for the engine system.
It provides spark for the combustion process to occur.
It removes heat from combustion chamber.

Always remember a spark plugs do not create heat, they help remove it. Anything that prevents a spark plug from removing the proper amount of heat can lead to pre-ignition, detonation, spark plug failure and even internal engine damage.

The spark plug acts as the thermometer of the engine. This “thermometer” can be used to effectively diagnose the amount of heat present in each combustion chamber. When interpreted correctly, spark plugs are valuable tuning tools.

They can reveal a great deal about the engines overall condition. By looking at the spark plugs firing tip, you can determine the engines operating condition, like get a feel for air/fuel ratios and even drivability problems.

As spark plugs grow older, they lose their sharp edges and material from the center and ground electrodes is slowly eroded away. As the gap between these points grows, the voltage required to bridge this gap increases proportionately. The ignition must work harder and there is a greater rate of misfires or incomplete combustion cycles.

Replacing worn out spark plugs is very important.

It will effectively restores the ignition system efficiency. How long spark plug will last depend on a variety of factors. Including engine compression, fuel used, gap, center/ground electrode material and the condition in which the engine is operated.