Diesel Glow Plug Function, Failure Symptoms and Replacement Cost

Last Updated on October 27, 2019 by themechanic

Diesel engine systems have a particular component called a glow plug. The main function of the glow plug is to help start the diesel engine. Basically, a diesel engine requires a certain amount of heat to start running properly. The glow plug provides this heat so that a successful ignition can take place.

There are two things which can reduce the heat if there is no glow plug. First, the cold temperatures of the weather outside can negatively affect the ignition process of the diesel engine. Second, the cylinder block and cylinder head absorb heat during the operation of the vehicle.

As a result, the glow plug is placed within the combustion chamber to attract more heat to the diesel engine. That allows the engine to continue functioning normally and keep the vehicle moving.

Glow plugs are like the spark plugs found in gasoline-powered vehicles. The difference is that glow plugs produce more heat than spark plugs. This extra heat is needed to ignite a high-powered diesel engine, especially in colder weather.

Top 5 Symptoms

When your glow plug goes bad, the signs will be more than obvious. Below are the top 5 symptoms of a failing diesel glow plug.

1) Weak Acceleration

It is possible to start your engine with a bad glow plug. However, the vehicle’s performance on the road will be less than satisfactory. You’ll end up stepping on the accelerator and not going as fast as you normally would. This should be a clear sign that something is wrong in your engine. It might not necessarily mean that your glow plug is bad unless you experience some of the other symptoms on this list.

2) Trouble Starting the Engine

You need a functional glow plug to start your diesel engine. If the condition of your glow plug is too bad, then it won’t be able to generate enough heat to get the engine running. It may take multiple attempts before your engine finally turns over and stays running. But if you don’t replace the glow plug soon, a point will come when your engine never starts running again.

3) Check Engine Warning Light

The Check Engine warning light should illuminate on your dashboard whenever there is any kind of issue with your engine. Since a bad glow plug affects the engine, then you can expect the warning light to activate. Of course, there are several other possible causes of this light coming on. Pay attention to the other symptoms to determine whether the glow plug is at fault.

4) Black Smoke

The diesel combustion process should never cause black smoke to emit from the exhaust pipe. But when you have a bad glow plug, it’ll cause problems for the diesel combustion process. Black smoke is one visible sign of these problems. Although, there could be a problem with another component in the vehicle which is causing the black smoke too.

5) Bad Fuel Economy

Since your diesel engine will perform very poorly because of the bad glow plug, it’ll require more diesel fuel to be consumed. Like with a gasoline engine, a stressed-out diesel engine consumes more fuel too. Replacing the faulty glow plug with a functional one will fix the problem.

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Replacement Cost

If you need to replace your diesel glow plug, the replacement cost will be between $125 and $250. The labor costs alone are only about $100 or $200, depending on the make and model of your vehicle. It shouldn’t take the mechanic more than 2 hours to complete the replacement job. The cost of the diesel glow plug part is between $25 and $50. So, it is very inexpensive to purchase this part. The labor will cost you more money.

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