All Glow plugs have the same purpose.  The difference is quality! There are single coil and dual coil plugs. Single coil plugs will burn out if constant power is applied, while dual coil plugs will regulate their temperature and not burn out.  

 WAP dual coil design regulates the plug's temperature to avoid catastrophic failures.  The dual coil design provides for faster start, less smoke at start-up, and longer life.

Glow plugs will wear out at some point in time.  Below are a few signd of wear.  When a glow plug wear out, it is important that ALL plugs are replaced.  Over-voltage is the most common failure of a glow plug.  To ensure a longer life span, you should use WAP dual coil glow plugs (see my store). 

 All of WAP glow plugs are tested twice before they leave the facility resulting in a defect rate of only .00007% of 7 pieces per MILLION!  

Common Signs Of Failure

Hard Start Cold -

No Start Cold -

White Smoke -

Solution:  Clean your controller from any contamination it might have.  A Q-tip does wonders.  Relace your glow plugs and/or relay controller.