As I'm certain Larry Bible (the self-appointed frequent/hot oil change proponent) will tell you, there are indeed oils manufactured specifically for diesels. Personally, I use Shell Rotella. Chevron Delo, and the new Mobil1 Delvac(?) are others with the diesel grade specification. I think they have higher detergent contents or something...

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Matt
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Grey/black '84 300D, 194K