Glow Plug discoloration and Diagnosis..

[Morgonzo]

I remember a thread where there was a picture of the different ways a glow plug can look coming out of an engine...

Carbon build up
white residue
broken tips
ect..
i cannot find this for the life of me. Does this thread exist? I'm personally dealing with whitish discoloration on some old plugs from the 80's.

Thanks for any help offered