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Spark plugs and glow plugs: what’s the difference?

This is a good question. Let’s start with the main similarity. All combustion engines need three things: fuel, air and heat or an ignition source. Both spark plugs and glow plugs are the ignition source in a combustion engine. So, what’s the difference? The short answer is the type of engine they’re found in. Spark plugs are only found in gasoline engines and glow plugs are in diesel ones.

But why do the two engine types have a different starting process? What do spark plugs and glow plugs actually do? And how do they fulfil their role to help start your engine? Continue reading to find out.

Spark plugs

What is a spark plug?

A spark plug is an essential part of your ignition, as your gasoline car won’t start without it. Basically, it’s an electrical component that can be found in your engine’s cylinder head where it receives a high-voltage charge from the connected ignition coil. The charge runs through the spark plug to the electrodes where it jumps the gap as a electrical spark causing combustion.

What does a spark plug look like?

Spark plugs have a central conductor, surrounded by an insulator and covered by a shell. The insulator is usually made from ceramic and is important for ensuring the spark only happens at the tip of the electrode. As the spark plug is located in the wall of the combustion chamber, it has to perfectly fit so that the combustion chamber remains sealed against high pressures and temperatures for long periods of time and extended use. Spark plugs come in a variety of types (copper, platinum or iridium), sizes (thread or nut), sealing type (taper or crush washer) and spark gap.

How does a spark plug work?

A spark plug works continuously to ensure your engine running. In a gasoline car, the fuel is mixed with the intake air in the throttle body before being injected into the combustion chamber. The spark plug receives a high-voltage charge from the ignition coil, causing it to spark and ignite the fuel-air mixture. This process is repeated thousands of times per minute.

Glow plugs

What is a glow plug?

It is possible to start a warm diesel engine without using a glow plug, or in warm climats, thanks to the relatively high temperature of the intake air and the relatively low ignition temperature of diesel. However, this isn’t enough to ensure proper ignition of the injected fuel in all temperatures, which results in increased exhaust emissions. A glow plug solves this issue. It is an electrical heating device located in each cylinder of the diesel engine that ensures reliable starts in all weather conditions.

What does a glow plug look like?

A glow plug is a long, thin piece of metal with a heating element at the tip. The heating element is constructed from materials that resist oxidation and high temperatures.

How does a glow plug work?

Unlike a spark plug that is working continuously while you drive, a glow plug is only needed during the ignition process. The glow plug works by electrifying the heating element so it heats up and emits visible light (hence the name). Intake air is compressed before the fuel injector spray directs fuel onto the hot tip of the glow plug during the injection of the fuel. The injected fuel mixes with the compressed air, evaporates and starts combustion almost simultaneously, even when the engine is cold.

Champion spark plugs and glow plugs

If you’re experiencing trouble with your current spark plug or glow plugs, be a Champion and consult the Champion Trouble Tracers. Full of hints and tips on how to identify and solve possible problems and the effect these problems could have on your engine.

view trouble tracers


The content contained in this article is for entertainment and informational purposes only and should not be used in lieu of seeking professional advice from a certified technician or mechanic. We encourage you to consult with a certified technician or mechanic if you have specific questions or concerns relating to any of the topics covered herein. Under no circumstances will we be liable for any loss or damage caused by your reliance on any content.

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