Over the last few years I have noticed that my glow plugs do not last very long. In the past, 3 to 4 years and must change two or three because of hard starting. (Hard starting for me when the engine does not start within seconds of cranking, bad for the starting motor)
Recently noticed a glow plug I replaced last year was bad this year which makes me think the life cycle of a glow plug has been reduced to 1 year...and now I see another MB owner had plugs go bad after a year. Make me speculate that the life cycle has been reduce making higher profits for the manufacture and our costs go up.....
My method of when to change a glow plug is to look at the threads on the plug. The more the dis-colorization, older the plug, and it gets changes.....so far always removed a back tip plug.

Bill
1981 300 TD


Bill