The glow plug is used in a diesel engine instead of a spark plug. The primary function of a glow plug is to produce heat in order to help with the startup process in the engine. Unlike a petrol engine, the fuel that is injected into a diesel engine does not need a spark to ignite it. But when starting a diesel engine in cold conditions, some extra help is required, which is where the glow plug comes into action.
Usually either platinum, iridium, or ceramic with an internal heating coil, a glow plug is a rod shaped heating element which can withstand extremes of high temperature. One end of the glow plug has a point which heats up, emitting a glowing light, when fed electricity. Glow plugs are normally installed in the cylinder head and are wired up to the car's battery.
The cylinders in the engine are heated up by the glow plugs before the engine is actually started, once the ignition has been turned to 'On' by the driver. In modern vehicles the glow plugs are usually automatically switched off by the glow plug relay when the desired heat has been reached to start the engine. Older vehicles require the driver to start the engine once given the go ahead by the indicator light on the dashboard, at which point the glow plugs switch off. If the engine is not started after a certain period of time, the glow plugs will be switched off automatically. If the engine is started prematurely this can cause damage to the glow plugs.
It is important to ensure the glow plugs on your vehicle are in excellent condition and working well. Signs that the glow plugs may need changing on your car are an engine that struggles to start or won't start at all. It is always a good idea to consult with your mechanic when engine problems strike, to make sure the correct fault has been identified. When you need to change the glow plugs, a good quality glow plug will guarantee a part that fits well, performs properly and has a long service life.