How to Free a Stuck Glow Plug

Updated July 20, 2017

The glow plugs inside of a diesel engine are the components that preheat the fuel/air mixture. This helps ignite the diesel fuel inside the cylinders. Excessive heat, carbon build-up and time can cause glow plugs to become stuck in the cylinder head. The absorption of penetrating oil around the threads of the glow plug will allow the plug to free up from the cylinder head.

Spray the threaded area of the stuck glow plug with a generous amount of penetrating oil. Allow the penetrating oil to absorb into the threads of the glow plug for about 30 minutes.

Place a 1/2-inch drive 6-point socket over the top of the glow plug. Insert a 1/2-inch drive extension into the end of the socket. Slowly turn the socket with a 1/2-inch drive ratchet back and forth about one-eighth of an inch in both directions to loosen the glow plug up from the cylinder head.

Slowly attempt to turn the ratchet counterclockwise once the glow plug has loosened. If the glow plug is still too tight, remove the ratchet and socket and respray the threads of the glow plug with the penetrating oil. Wait thirty 30 minutes to 1 hour for the penetrating oil to absorb into and around the threads of the glow plug.

Slowly attempt to turn the glow plug counterclockwise again with the ratchet and socket. Once the glow plug loosens, finish loosening and removing the glow plug with the flexible piece of vacuum hose. If the tip of the glow plug is swollen, the barrel will come off of the glow plug and leave the probe inside the head. In this case, on Ford Power Strokes, the adjacent rocker arm and push rod will need to be removed before the glow plug can be removed.

Loosen and remove the nuts to the adjacent rocker arm with a ratchet and a socket. Pull the rocker arm off and pull the push rod out of the cylinder head. Place the rocker arm and the push rod to the side. Pull the barrel off of the glow plug and grab the probe with the needle nose pliers. Spray the penetrating oil around the base of the probe. Have a helper hold the probe with the pliers.

Gently tap down on the top of the probe with a centre punch and a hand held sledge hammer to free the stuck probe up. Move the probe up and down with the pliers until the probe works itself out of the hole. Spray more of the penetrating oil as necessary to help loosen up the stuck glow plug.


Wear safety glasses when spraying the penetrating oil and when using the bottle torch.

Things You'll Need

  • Safety glasses
  • Penetrating oil
  • 1/2-inch drive ratchet
  • 1/2-inch drive extension
  • 1/2-inch drive 6-point socket set
  • 6-inch piece of flexible vacuum hose
  • Needle nose pliers
  • Center punch
  • Hand held sledge hammer
Cite this Article A tool to create a citation to reference this article Cite this Article

About the Author

Kevin Mclain has more than 20 years of automotive, home improvement and landscaping experience. He has been writing for various online publications since 2002. Mclain has U.S. Army certification in automotive maintenance and repair, among more than 15 additional certifications related to the automotive field.