How to Change the Glow Plugs


This is another simple replacement that you can perform on your car. Diesel engines have, unlike petrol engines, glow plugs that heat up the engine cylinder before the fuel injection. This is crucial for the ignition to happen, otherwise the fuel doesn't achieve the needed temperature for combustion. Therefore, when your diesel car has problems with starting (cranking but not starting), in the morning or in cold temperature, this is the number one reason. Remember, one glow plug going off line is enough for your car not to start.

Glow Plugs Position and Tools

You'll find the glow plugs in the same position where the spark plugs would be (on the cylinder head). They will have a copper rail connecting them together and a thicker cable connected to the rail. The rail and the cable are responsible for the proper electric input to the glow plugs.

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Glow plugs position on the engine
The tools you'll be needing are :
  1. Set of wrenches that match the job.
  2. A pair of players (possibly with long extensions, for getting to those hard places)
  3. A magnet (the one that looks like a screw driver (if a screw or nut falls into the engine space and you can't reach it by hand)

Changing Glow Plugs Procedure

  1. Make sure that ignition is turned off. If your not sure take the minus terminal of the battery.
  2. Disconnect the main input cable (the one that comes from the installation to the rail).
  3. Disconnect the main rail connecting the plugs. Take off the screws that connect the rail to the glow plug. Do this one-by-one. This is where the magnet comes in. These screws or nuts are usually very small so there is a possibility that they are going to slip from your hand. Use the magnet to get them out. Don't be lazy to find it because it could fall in to a critical part of the engine space and cause damage.
  4. Take the proper wrench and take off the plugs. Do this one at a time. If the plug is going hard, take your time. Try spraying some anti-corrosion adhesive to the plug and wait. This is better than the plug breaking in two which leads to major problems (taking off the engine head).
  5.  Put the new plugs in. Be sure that you have the same plugs that the manufacturer has put in. Screw them tightly back.
  6. Put the rail back on. Be sure that the rail is fitted on tightly. Put the nuts back on the plugs and tighten them.
  7. Reconnect the main feed cable to the rail and plugs.
  8. Turn on the ignition switch, see if the glow plug light on the dash is working (turning off when the plugs are warmed up). Start the car, if it starts normally (without long cranking) the job is well-done.

As I always say, take a good look under the hood for the positioning of the glow plugs. If they are in a bad or heavy-to-reach position think twice before doing anything. This is a job where you''ll need to be armed with patience and time. Otherwise, let a mechanic do it. To make a proper check of the plugs you can read "Checking the glow plugs" tutorial.