I believe you can check those glowplugs by feeling to see if they are at all warm after glowing. Put you fingers on them on a cold engine, glow a couple of cycles and feel them again. Be careful not to burn yourself. If these are series plugs (which I doubt) you can tell if they are working by seeing if the heavy wire glows red when they're on.

Cold temperatures will cause the problem of low compression to suddenly appear.

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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