I have been experimenting with this recently since I traditionally always waited until the glow light went out. I'm finding that once the engine is at operating temperature and I only shut it off for a short period of time, the engine fires up immediately without waiting for the glowlight. If the engine is slightly warm, and I do the same thing, it takes an extra revolution or two before it fires up. With a little practice, I'll know when using the glowplugs will reduce starter strain of about 2 seconds when the engine is not quite hot enough.

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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