My 85 300td does the same thing and I'd like to get a clear understanding of what is happening. I've posted on it in the past but haven't got a satisfactory answer. I did replace the glow plugs but no difference. It starts right up at first crank even at 10 below zero. Once in a while it will do it when warm also but that is fairly rare.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13