I've heard there's a difference in durability between the old style coil glowplugs and the later quick-heating pencil type plugs on Mercedes diesels. I just changed the 6 glowplugs on a friend's 1986 524TD BMW. (Yeah, I know it's not a Benz but I hoped some of the diehard Diesel fans here would have an answer. I don't think there's any good BMW Diesel sites.) 5 of the 'old' glowplugs were bad. Thing is, I changed them about 3 years ago. They're the 'quick-heating' pencil type plugs. Is it normal for these to fail after 3 years?

Thanks All, Mark

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DrDKW