Symptoms of a Bad Diesel Glow Plug (and Replacement Cost)


In this post we are going to explain about one part on diesel engine systems, known as glow plug. So you will know the basic function, failure symptoms and replacement cost. And here we go:

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Glow Plug Function

A vehicle with a diesel engine needs a diesel glow plug to help it start. This plug device generates the necessary heat that is needed for a diesel engine to run and function properly, especially in climates where the weather is cold.

But it isn’t just the cold weather that reduces the heat needed for ignition to take place. The heat also gets absorbed from the cylinder head and the cylinder block as well. To bring heat back to the engine, the glow plug is installed inside of the combustion chamber.

Glow Plug vs Spark Plug

Do not confuse glow plugs with spark plugs because they are two different components. Spark plugs are what help a gasoline vehicle generate the spark that is necessary for it to ignite the fuel and air mixture in the combustion chamber.

Diesel vehicles, however, do not use spark plugs because they don’t generate enough heat for the mixture in the combustion chamber. Since the cylinder compression is more intense in a diesel engine, it needs more heat to generate an ignition because the compression heat by itself is not enough.

Only a glow plug can provide the additional heat that is necessary for a diesel engine to start up and function.

Bad Diesel Glow Plug Symptoms

In a situation where the glow plug becomes faulty and stops functioning properly, the combustion chamber will not have the additional heat it needs for an ignition. Sometimes you may be able to get an ignition after multiple attempts of trying to start the vehicle, depending on how cold the temperature is outside.

But if you’re in a northern climate with freezing temperatures, you likely won’t get a diesel engine to start at all if the glow plug is bad. If you find that you’re regularly having trouble starting your vehicle, even if it eventually does turn on, then you should have your glow plug tested right away.

Of course, if you have a diesel engine that doesn’t start, you wouldn’t necessarily assume right away that it’s the fault of the glow plug not working. That is why you must look out for additional symptoms as you attempt to start the engine.

For example, if you see black smoke coming out of your vehicle as you attempt to start the engine, this is a sign that the combustion of fuel and air in the chamber was not successful. This black smoke is the result of unused fuel that didn’t properly go through the combustion process. Once again, this is the fault of the glow plugs being bad.

If you’ve already gone through all these symptoms and your diesel vehicle still drives, it probably won’t be performing all that well. You should notice that your engine is performing poorly by losing acceleration, fuel economy, fuel efficiency, and overall power.

These are certainly not safe driving conditions to operate any vehicle with. Therefore, have your vehicle towed to the nearest auto body shop so they can diagnose the problem with the glow plugs for you.

Even if the problem ends up being something else, at least you’ll be getting the problem fixed rather than continuing on under these dangerous conditions.

Diesel Glow Plug Replacement Cost

For replacement parts, we recommend:

The good news is that it’s not terribly expensive to replace a glow plug. The average cost of the parts will range from $25 to $50 and the labor costs for the replacement job will be about $100 to $200.

Although the glow plug itself is cheap, it will take the mechanics about 1 to 2 hours to replace your faulty glow plug. Since mechanics typically charge about $90 to $100 per hour, you can expect to pay more for the labor than the actual part itself.


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