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What are glow plugs?

What are glow plugs?

Glow plugs are used in diesel engines to start your vehicle. They bring the combustion chamber up to temperature. Glow plugs are essential in diesel-powered vehicles and also help limit the release of particulate matter into the air.

All diesel vehicle owners are probably aware that their vehicle is equipped with glow plugs. But do they know what they do?

What does a glow plug do?

First and foremost, glow plugs are starting aids for diesel engines. They are easily recognized by their pencil-like shape.  They allow the combustion chambers of the cylinders to be properly preheated before and during engine startup.

Unlike a gasoline engine, a diesel engine must be heated to a certain temperature before it can start. In particular, the air that ignites the fuel must be hot enough to start the engine. A glow plug solves this problem. It is an electrical heating device located in each cylinder of the diesel engine that ensures reliable starting in all weather conditions.

What are they made of?

Mostly metal and/or ceramic. At the end is a heating coil. These are electrical resistors that heat up under the effect of electrical voltage. They can heat up to 1050°C in just 12 seconds.

Its classic composition has a central rod that connects the two spark plug connectors, one of which contains the ignition coil. The coil body is made of ceramic. Modern spark plugs are of the "double spiral technology pencil plug" type, which is thinner and longer. The latter type is more reliable and allows for faster preheating.

Where are the glow plugs located?

The location of the glow plugs depends on whether the engine has direct or indirect injection. On older indirect-injection diesel engines, the glow plug is located in the combustion precombustion chamber, next to the injectors. Modern diesel engines all have direct injection. Both the glow plug and the injector work directly in the cylinder.

How does a glow plug work?

An electrical voltage allows current to flow from one end of the glow plug to the other. The current then flows to the heating filament, which reaches a very high temperature and becomes incandescent.

This allows the air in the combustion chamber to heat up and ignite the diesel fuel so that the air-fuel mixture is at the correct temperature.

In practice, this means that the driver waits a few seconds after turning the key to the glow position until the glow indicator lights up. The glow plug consists of a heating element screwed into the cylinder head which, when electrically energized, heats the combustion or pre-combustion chamber in or above the cylinder (depending on the type of injection).

A difficult life to determine

It's difficult to determine the average life of a glow plug: everything depends on the brand, how often your car is started, climatic conditions, etc. On average, a glow plug should be replaced every 100,000 kilometers.

What are the risks of delaying the replacement of my glow plugs?

Today's glow plugs have a post-heating function. In other words, even if the engine starts properly, one or more glow plugs may be damaged. And if one glow plug is defective, the others will gradually become so.

Faulty glow plugs can cause difficulty starting, damage to the particulate filter (or DPF), noise and vibration, excessive pollution when starting, and even failure at very low temperatures.

How much does it cost to replace glow plugs?

We strongly recommend that all glow plugs be replaced at the same time to prevent imbalance between cylinders when the engine starts. You should expect to pay between $10 and $20 for a glow plug, plus labor if you go to a shop.

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