FAQ #182
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What is a 'Glow Plug'
A glow plug is simply a starting aid on a diesel engine.

Once the engine has started it relies on air, fuel and compression. There are a few types of glow plugs in use in vehicles. The older "loop" style were large and had a simple loop of a heavy special wire protruding from the end that got red hot and heated nearby air up in either a pre-combustion chamber or on some diesels like older Perkins in the intake manifold.

Perkins actually had a fuel line with a valve connected to the intake style that when the element got hot enough it would open the valve and let a drop or two of fuel hit the hot element to vaporize it and aid starting. Both of these types had very long pre-heat periods compared to todays "pencil" style glow plugs.

"Pencil" style glow plugs are all encased and simply come to a smooth point or blunt end. The tip of these gets red hot rather than a loop or coil of wire. These glow plugs run at a lower voltage than the older styles and heat up much faster resulting in quick start up times and less draw off the battery for better winter starts.

Some systems have a timer that works with a temperature sensor that "cycles" the glow plugs on and off until the coolant reaches a certain temp. There are also coolant glow plugs that aid in warming the coolant faster so the engine warms up quicker to burn the fuel more efficiently.
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FAQ Posted by C6Dave
Info Created: 07 October 2009
Last Updated: 07 October 2009