What is a Glow Plug and What Does it do?

Have you ever heard of a glow plug? If you've been driving cars that use petrol, chances are you've never come across a glow plug. These car parts are used only in diesel vehicles. However, they do have the same kind of functionality as spark plugs. Only instead of sparking an ignition like a spark plug does, these parts are responsible for heating air that results in ignition of an engine.

What are Glow Plugs?

In short, glow plugs are small heaters that live inside the bonnet of a diesel-powered car. These car parts are actually not necessary all of the time. You see, unlike petrol fuel, which requires a spark to ignite a mixture of air and fuel and start the engine, diesel fuel only needs to be hot enough and under enough pressure to self-combust. In hot weather, the fuel can typically achieve this feat on its own, requiring no other car parts to help it do it.

In cold weather, however, things are different. It's much harder for the diesel fuel to ignite, preventing the air and fuel mixture from starting the engine. That's where the glow plug comes in. It act as a little heater that increases the temperature of the diesel fuel so it can ignite.

Most glow plugs are made up of several components, including the heating coil, regulating coil, terminal nut, centre electrode and thread. Insulation powder is also present, separating the coil from the heater tube. The outside is covered in a metal or ceramic shell.

Types of Glow Plugs

There are several types of glow plugs available today. Your particular car's make and model will determine what kind of glow plug you should use. None of them are interchangeable. Some types of metal-sheathed glow plugs include:

• Standard

• Quick start

• Quick glow system

• Self regulating metal

Ceramic glow plugs are also available in two different types: self regulating ceramic and new high temperature ceramic. In each kind, the maximum temperature and voltage created by the glow plug varies.

Symptoms of Bad Glow Plugs

Because glow plugs provide such a necessary service to your diesel engine, driving your car can be very difficult when one is failing. Knowing the signs and symptoms of a worn-out glow plug can help you address the issue before you're left stranded without a way home.

• Warning Light- Many of today's vehicles come equipped with sensors that help you determine when a problem is occurring so you can fix it fast. This is true when it comes to glow plugs. If you're driving your Peugeot and notice an usual warning light on your dash, pull over as quickly as possible to read your owner's manual and determine what the problem is. Faulty glow plugs can cause a warning light to come on when a temperature sensor has gone bad, the glow plug itself is corroded or the relay for the glow plug has become disconnected.

• Hard Starting- If you were driving a car with a petrol engine, and it started hard, the first thing you'd look at would be the spark plugs. The same can be said about a diesel engine. The third place you need to look, after the battery and the fuelling system, is the glow plugs. If these Peugeot parts aren't working, the combustion chamber can't ignite the fuel.

• Strange Behaviour- Even if you're able to get your engine started on a bad glow plug, it can still continue to affect your vehicle until the car becomes warm. You might notice the engine misfiring as you drive down the road. Listen for it as you shift gears. If the car isn't idling well or you feel the piston misfiring until the car is able to warm up (about 10 minutes into driving) you should check the glow plugs to see if they are working correctly.

• White Smoke- Smoke near a car can be extremely scary, but it could also help you diagnose problems with Peugeot parts. White smoke coming out of your exhaust when you first start the car, for instance, can indicate that a glow plug has been disconnected, resulting in fuel leaking out of the chamber and into the car's exhaust. This fuel is then ignited in the exhaust, producing the white smoke you see. While this will often go away after about five minutes, the problem won't and needs to be fixed.

Keep in mind that the number of glow plugs required for your vehicle will often determine exactly how troublesome the symptoms you get are. For instance, you may experience a few misfires and some hard starting if your engine requires one glow plug. However, if it requires three, a bad glow plug could prevent you from starting and operating the car at all.

Checking Glow Plugs

If you have a multi-meter, you can easily check your glow plugs to see if they are functioning correctly. To do this, you'll need to disconnect them. Attach the clip of the volt test to the positive terminal of your battery and the probe to the glow plug terminal. If the test light doesn't illuminate when you touch the probe to the terminal, you will know that particular glow plug isn't working correctly. You can also use an ohmmeter to do this test. You'll need to measure the difference between the ground terminal resistance and the resistance of each glow plug. If the glow plug shows more than just a couple of ohms, it is most likely bad.

Making sure your Peugeot runs well is important, and that starts with being able to turn it on. In order to do this with a diesel engine, you need glow plugs that are whole and ready to be used. Any worn glow plug could result in problems, so check yours regularly.