If you consistently get temperatures that cold, you need a block heater in my opinion. If a long extension cord won't work, a small generator might. At those temperatures, everything on the car needs to be up to snuff. Good glow plugs with no carbon around them, good compression, top notch battery, good starter, winter fuel or additives in the fuel.

Thinking a little outside the box, if you have a gasoline car that starts, you could put quick release connections in the hoses on the coolant system, start the gas car, circulate the hot coolant from the gas car thru the diesel until it gets warm, start the diesel and disconnect the cars.

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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