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Diesel Truck Maintenance: What You Should Know About Glow Plugs

Sales in diesel vehicles are increasing all the time as an alternative to the traditional gas engine. Once reputed to be loud and odorous, diesel engines no longer are. With new technology and standards, and the help of innovative glow plugs, diesel trucks are quiet and maintain high environmental standards.

There are a few important differences between traditional gas engines and diesel engines that make drivers choose diesel. Drivers of diesel vehicles have made this choice because they know that their truck has more torque and towing power than gas trucks. They also know that they have better fuel mileage.

Many diesel owners don’t know what glow plugs are, however. Read on to find out more about how they work and your options. You’ll be glad you did.

What Are Glow Plugs?

In a gas engine, the spark plugs start the engine by emitting a spark that ignites a gas and air mixture generating power for the motor. A glow plug has the function of heating the fuel under pressure to allow it to self-combust. No spark is required for this function.

Glow plugs are like small heaters inside the hood of diesel engines. Every make and model of diesel engine requires a different number of glow plugs. This is because there has to be one glow plug per cylinder and there are different numbers of cylinders in each engine. 

How Do Glow Plugs Work?

A glow plug is similar to a heating coil inserted in a tube. It looks a lot like a spark plug with a pencil-like shape. It is usually is made from a high heat-resistant metal, like platinum or iridium. It has a heating element on its end with a temperature sensor.

The glow plugs have screw-in threads and a single-pole connecting pin glued to the housing using a non-releasable aluminum nut.

If you’re looking for your glow plugs, you can usually find them in the pre-combustion chamber of your diesel engine or the combustion chamber.

Glow plugs function with heat and pressure. Diesel engines require heat to start, especially in low-temperature weather conditions. The glow plugs supply this need as follows:

1. Pre-heating

The heating coil inside the glow plug quickly generates heat for the fuel. Depending on the glow plug, the temperature of the unit can reach over 1000°C within seconds.

2. Compression

The air intake valve in the cylinder closes. The piston rises, compressing the air to 6% of its former volume. 

3. Ignition

The piston reaches its highest point. The fuel heated by the glow plug is injected into the combustion chamber, combines with the compressed air, evaporates, and ignites.

4. Temperature Maintaining

The glow plugs keep the heat maintained for at least 3-5 minutes to ensure combustion continues. This also helps reduce the number of emissions and the build-up of soot that is trapped in the regeneration filter. This also helps with the noise output as the combustion chambers are heating up.

In sum, you turn your engine switch on and wait those few seconds for the light to go off. Immediately, an electric current passes through the heating element and the glow plugs heat the fuel. After the light goes off and you start your engine, all the processes described above occur within your engine.

When Should You Replace Your Glow Plugs?

There is a whole relay of glow plugs inside your engine, waiting to heat the diesel fuel to start the whole process of ignition. As mentioned before, the number of glow plugs will depend on the number of cylinders in the engine. If you start having problems with your glow plugs, it could be just one plug or it could be the electrical system that connects the glow plugs.

Here are some signs that there are problems with your glow plugs.

A Warning Light Goes On

Many diesel-powered vehicles come equipped with sensors that will notify you of a problem. You may have a Check Engine light or even a Check Glow Plugs light.

A faulty glow plug will illuminate the Check Engine light, as will numerous other problems, so this would warrant investigation and does not guarantee the problem is with the glow plugs.

It’s Difficult to Start Your Engine

Heating glow plugs are what is required to generate the necessary heat to ignite the fuel. Your vehicle won’t start without this heat. It can, however, be the battery and the fuelling system, so these need to be checked first.

Black Smoke

You should never get black smoke from the exhaust pipe if your diesel engine is functioning properly with proper combustion processes. If you have a malfunctioning glow plug, you may get improper heating of the fuel in some cylinders causing black smoke. 

Again, malfunctioning glow plugs are not the only possible reason for black smoke, so don’t rule out other possibilities.

Weak Acceleration or Engine Misfiring

Your truck will still start, even with a bad glow plug. Your acceleration will be affected however since not all cylinders are receiving the heated fuel in the way they should. You may also have problems with your engine misfiring.

Once again, don’t rule out other problems unless you have other symptoms listed here. 

Poor Fuel Economy

A stressed-out diesel engine, just like a gasoline engine, will perform poorly and consume more fuel. Replacing a faulty glow plug with a good one will fix this problem of excessive use of diesel fuel.

What To Do If Your Diesel Truck is Having These Problems

You should always get regular diesel engine maintenance. If your mechanic determines one glow plug isn’t working properly, you might as well replace all of your glow plugs, because you can be certain the others will likely start to fail soon.

One of the main issues with diesel engines can be the electrical system. Any misfunction in this system may mean your glow plugs are not functioning properly.

Getting a qualified mechanic to do your diesel truck repair and maintenance can prevent a lot of problems. Contact us today if you are experiencing any of the problems listed above and we’ll check to see if it’s a simple problem like glow plugs and get everything in tiptop shape for you.

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