How To Replace Diesel Engine Glow Plugs

22 August 2016
 Categories: Automotive, Blog


If you have a vehicle with a diesel engine that is slow to start, fails to start, idles rough, or has white smoke from the exhaust, the glow plugs may have malfunctioned. Some systems use an indicator light to warn you of issues. Diesel engines use glow plugs to start the engine instead of spark plugs. You can replace the glow plugs yourself without professional help. Here are tips to replace diesel glow plugs.

Prepare to Work

For this project, you need:

  • work gloves
  • safety goggles
  • rags
  • jack stand
  • screwdrivers
  • socket wrench and ratchet set
  • penetrating oil
  • glow plug reamer
  • glow plugs

Park the vehicle on a flat surface, but not on dirt or grass, and lift the vehicle on a jack stand. Let the engine cool for several minutes.

Keep a fire extinguisher handy in case of gas fires. Don't let anyone come in the area smoking, because smoke may ignite vapors. Wear safety goggles to protect the eyes from possible fluid spurts from the battery.

Remove the Old Glow Plugs

Open the hood and disconnect the negative wire from the battery with a socket wrench. A negative wire is commonly black, but if there are two black wires, look for a plus or minus sign. The clamp should come out after you remove the wire.

Look for the glow plugs on the cylinder head. The wiring is located under the engine block. If there is a valve cover on the engine block, use the screwdriver to remove the screws and set the cover and hardware aside.

You will find a wire connected to the engine and another wire connected to the glow plugs. Disconnect the nut on one wire at a time with a wrench.

Attach a deep well socket to a wrench. Place the wrench on the glow plug with the deep well socket end in the hole, and turn the wrench counterclockwise. Loosen the glow plugs enough to remove by hand.

Install the New Glow Plugs

Inspect the glow plug terminals for dirt and wipe them with a rag. Insert the reamer into the plug hole to clean it.

Spray a thin coat of penetrating oil on the glow plugs for better performance in cold weather. Insert the new plugs into the holes, and use the wrench to tighten them until they are hand-tight.

Reconnect the engine block cover, if needed, and reconnect the glow plug wires. Reconnect the battery wire, and test the engine.

It is important to check on diesel engines and have them serviced periodically. If you don't trust your skill, the vehicle still fails to work properly, or the vehicle has't been serviced in quite some time, take it to an automotive service such as Bethel Automotive.