5 Symptoms of a Bad Diesel Glow Plug in Your Car


To start a diesel engine successfully, it will need a special heating component called a diesel glow plug. A diesel engine cannot start and operate properly without the heat generated from this plug. If you normally drive your diesel-powered vehicle in colder environments, your engine will rely on the diesel glow plug to generate the necessary heat it needs to function. Otherwise, the cold temperatures would make it impossible for the vehicle to start up. In addition, the cylinder block and cylinder head will be absorbing a lot of this heat too. Since the diesel glow plug is positioned within the internal combustion chamber, it will deliver this heat to the engine.

5 Bad Symptoms

You now know that the diesel glow plug is a necessity for the diesel engine to function properly. So, if the diesel glow plug were to become damaged or go bad for some reason, the symptoms would be easy to spot. In fact, the whole car’s functionality will change because of it.

Below are the top 5 symptoms of a bad diesel glow plug.

Difficulty Starting the Engine – Bad diesel glow plugs will make your car engine difficult to start up. Since the pressures in the cylinder are mainly responsible for igniting the diesel fuel after it’s been injected into compressed air, a bad diesel glow plug will place more pressure on the engine for this ignition to be successful. That is why it becomes hard to start.

Engine Misfires – When the fuel does not ignite properly in the cylinder, this will cause an engine misfire to take place. As you know, the diesel glow plug plays a vital role in making this ignition a success. If the plug is not functioning properly, there will likely be a misfire during ignition. You may still be able to drive your vehicle, but you will experience a downgrade from its normal performance.

Black Smoke – If you see black smoke coming out of the exhaust pipe, this could be an indication that you have a bad diesel glow plug. Of course, there could be several reasons for this black smoke, but a bad glow plug will certainly put a damper on the diesel combustion that takes place. Black smoke is not a normal part of this combustion process. Therefore, take this smoke as a warning sign that something must be wrong either with the diesel glow plug or some other vital component of the combustion process.

Weak Engine Performance – If the ignition of the compressed air and fuel is not sufficient enough and a misfire takes place, the overall performance of your vehicle’s engine will be reduced. One of the first things you will notice from this weakness is the low acceleration as you step on the gas pedal. In normal situations, stepping on the gas pedal will make you go faster. But with a bad diesel glow plug, you won’t be able to go faster after you step on the pedal. In fact, the longer this continues, the worst the acceleration power is going to get until the vehicle just doesn’t move at all.

Read also: 5 Causes of Car Engine Low Compression and Tips to Inspect

Low Fuel Efficiency – Once your engine’s performance becomes weakened, it will try to work extra hard just to meet the demands of your driving. With a bad diesel glow plug causing ignition problems, your car will lose out on its fuel efficiency. This means that your miles per gallon will be reduced, and then you’ll have to purchase more diesel fuel than usual. If you are already experiencing any of the other symptoms involving the engine, then it should be no surprise that you would have low fuel efficiency along with them.


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