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When it comes to maintaining your diesel pickup, there are some things you will have to consider with a diesel that you do not with a gas-powered pickup. One such consideration is the glow plug.

Close-up of four used glow plugs for diesel engines, captioned “What Diesel Drivers Should Know about Glow Plugs”


To start, a diesel engine requires the help of glow plugs. A glow plug produces the heat that is necessary for a diesel engine to start, run, and function optimally- especially in colder weather conditions. However, it isn’t only cold weather that strips away the heat that is needed for ignitions to happen. The cylinder block and cylinder head also absorb heat. To bring this vital heat back to the engine, glow plugs are installed in the combustion chamber.


People will often confuse glow plugs and spark plugs. However, they are two very different vehicle components. Spark plugs are responsible for creating the spark that ignites the fuel/air mixture in the combustion chamber of gasoline vehicles. Spark plugs are not used in diesel vehicles because they do not produce enough heat for the mixture in a diesel combustion chamber. Cylinder compression is stronger in diesel engines, so they require more heat to ignite. A glow plug is the only thing that can generate the additional heat needed to start and run a diesel engine.


When a glow plug fails to work properly the combustion chamber doesn’t have the extra heat that it requires to ignite. Depending on the outside temperature, there may be times that you can achieve ignition after several attempts to start your vehicle. However, in freezing winter temperatures, it is unlikely that a diesel engine will start at all if the glow plug is faulty. If you are having trouble starting your diesel vehicle, especially in the winter, have your glow plug tested as soon as possible.

Another sign that your glow plug is faulty would be black smoke coming out of the vehicle when you try and start the engine. This smoke indicates that the air/fuel combustion was unsuccessful. The black smoke results from the fuel that did not go through the combustion process properly because of a bad glow plug.

If you have experienced these symptoms and your vehicle still manages to start and drive, it likely is not performing very well. You will most likely experience the following problems:

  • Loss of acceleration
  • Poor fuel economy
  • Loss of fuel efficiency
  • Loss of overall power

These driving conditions can be unsafe and could result in further and more expensive vehicle damage. Bring your vehicle to us right away so that we can solve your glow plug- or any other- problem for you.

Gem State Diesel specializes in the repair and service of light, medium and heavy-duty diesel pickups. We were established in 2010 and have established a reputation for superior diesel pickup repair and service in the Boise area. Our team has ASE Master Certified diesel mechanics with extensive experience in the service and repair of diesel pickup engines. Call 208.957.6106 or schedule an appointment online.