is that minus 7 or around 7F?... and is that windchill temps? if it's winchill, then your car should start fine with good glowplugs. IF your car has good compression, good thin oil and a good battery.
if one or more of these are not up to snuff... good luck cranking and cranking.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!