How to replace/remove the glow plugs
Difficulty: 1/5
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Introduction

This article covers glow plug removal and replacement.  If you want to do compression testing, glow plug replacement, etc.,  they need to come out.  If you think that you need new glow plugs, first check the wiring, as faulty or corroded wiring may cause a misdiagnosis.  Note that glow plus are not a "it works or it doesn't" item.   As glow plugs wear out, they become weaker and could be contributing to a hard start condition.  You can also extend the glow plug duration through a vag-com program.  Also note that the manual transmission car uses 3 coolant glow plugs in the coolant flange out of the head for faster engine warm-up.  2004-2006 TDI use ceramic glow plugs which can be break if it is hit.  2009+ TDI use pressure sensing glow plugs. 

Procedure

First remove the glow plug wires.  Just gently wiggle and pry them straight out.  If you must, you can remove a fuel injector hard line to get more clearance.  Just be prepared to catch any fuel with a towel and make sure there is plenty of ventilation and no source of ignition or spark near.

Before you remove the glow plugs, you should clean the dirt around the glow plugs.  Use carb/brake cleaner and lightly spray and wipe the area around the plug.  Then use compressed air to blow out the area.  Make sure that you are wearing safety goggles as the compressed air will send sand into the air.  If you want, you can spray a little bit of PB blaster around the threads and let soak.  Wipe away any excess.

For VW, use a deep 10mm socket and universal joints to remove the glow plugs or VW special tool 3220.

Put anti-seize around the glow plug threads and replace.  Don't use too much antisieze.  Note:  wd-40 or other lubricants are not a substitute for anti-seize.  Please read 1000q: mechanics tips and garage organization for more information on this.  The link also has information on parallax, a viewing error.   

Beware of parallax when rethreading the glow plugs!  If it does not go in smoothly for at least a few turns, you may be stripping the threads.  On many VW diesels, the glow plugs do not go straight in at the same angle - the threads are not all perpendicular to the head!  One trick you can do is turning the glow plug/screw/adapter/bolt/etc., counterclockwise for a complete turn,  then turning clockwise to tighten.  The head is aluminum, so don't over torque it!  Torque to only 10-12 ft lbs.

New vs old plugs:

Glow plugs reinstalled with a new wiring harness.  The glow plugs are connected by a black wiring harness, the injectors are the ones with a metal hard line at the top and a black fuel return line below it.