Problem with Glow Plug..

[thisisthepart]

I've gone through two glow plugs in the last week.. I was wondering why this might be happening and what I can do to prevent this? Is my car too rich or too lean? And what kind of glow plug would be best for my Savage SS with a 4.6?

My main concern is that I'm ruining my engine.. Running it too lean and sucking the life right out of it.. I know its hard to give advice without knowing exactly what my engine settings are and what I'm doing to it - but in general, what are the main causes of glow plugs continuously failing?

 

[Bankrupter]

lean ... mill coming apart inside.. bad batch of plugs ,,, I have had two bad back to back now. So its not impossible.