Volume of fuel in the tank is probably irrelevant. You should be able to charge it by jumping. You could also use a battery charger. Could be a bad glow plug. Do you know for sure that all glow plugs are working? (I assume an 80SD has the parallel plugs)
Heating it up will do magic. Does it have a block heater? If so, plug it in. A magnetic pan heater can also be of some use if you don't have a block heater.
In a pinch, a bag of charcoal on a tray under the engine compartment might work as long as you make sure nothing catches on fire.

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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