Glow Plug Replacement

Glow Plugs Help Start The Diesel

Glow plug replacement is a critical maintenance task for diesel engines, ensuring optimal starting performance, especially in cold weather conditions. Diesel engines rely on compression to raise air temperature to a point where diesel fuel combusts spontaneously when injected into the combustion chamber.

Unlike gasoline engines, which use spark plugs to ignite the fuel-air mixture, diesel engines use glow plugs to preheat the air in the combustion chamber during cold starts, facilitating easier and more reliable ignition of the diesel fuel.

glow plugs

Understanding Glow Plugs

Glow plugs are electrically heated elements, similar in appearance to spark plugs, installed in each cylinder of a diesel engine.

When activated, they glow red-hot, significantly increasing the temperature within the combustion chamber to ensure the diesel fuel ignites promptly when the engine is cold. The glow plugs are controlled by a glow plug relay or control module that regulates the electrical current to the glow plugs, heating them for a specific duration based on the engine temperature and other factors.

Symptoms of Faulty Glow Plugs

  1. Hard Starting: Difficulty in starting the engine, especially in cold conditions, is a common symptom of failing glow plugs.
  2. Misfiring During Startup: The engine might misfire or run unevenly right after starting due to one or more cylinders not igniting properly.
  3. Decreased Fuel Efficiency: Inefficient combustion due to poor glow plug performance can lead to increased fuel consumption.
  4. Check Engine Light: The vehicle’s onboard diagnostics (OBD) system may trigger the check engine light if it detects an issue with the glow plug circuit.

Replacement Process

Replacing glow plugs is a straightforward yet delicate procedure, often requiring the following steps:

  1. Preparation and Safety: Begin by ensuring the engine is cool to prevent burns and disconnecting the battery to avoid electrical shorts.
  2. Access: Remove any components obstructing access to the glow plugs. This may include air intake manifolds, engine covers, or other parts depending on the engine design.
  3. Removal:
    • Disconnect the electrical connector from each glow plug.
    • Use a suitable glow plug socket and extension to unscrew and carefully remove the old glow plugs from their bores. Note that glow plugs should be handled gently to avoid breaking them, as broken plugs can be challenging to extract.
  4. Installation:
    • Check the new glow plugs for correct type and size.
    • Without applying any excessive force, manually thread each new glow plug into its bore to prevent cross-threading.
    • Tighten the glow plugs to the manufacturer’s specified torque setting using a torque wrench.
  5. Reassembly: Reconnect the electrical connectors, and reinstall any components removed for access.
  6. Testing: After replacing the glow plugs and reassembling any removed parts, reconnect the battery and start the engine to ensure it operates smoothly without misfires.

Hard Starting Diesel? Could Be Glow Plugs!

Glow plug replacement is essential for the maintenance of diesel engines, particularly for ensuring reliable starts in cold weather.

While the replacement process can be performed as a DIY task with basic mechanical skills and tools, it requires careful handling and adherence to manufacturer-specific procedures and specifications. In cases of uncertainty or complex engine layouts, consulting a professional mechanic or service manual is advisable to avoid damage to the engine or personal injury.

Regular inspection and timely replacement of glow plugs as part of routine maintenance will contribute to the longevity and efficiency of diesel engines.


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