it will start fine with the block heater. I drive a bus, and I'll take the bus out at 6:30am and plug my car into where the bus was and I'll occationally just get a lift home or ride my bike, leaving the diesel plugged in well over 24 hours in snow and well below zero temps and it will start up with 2 revs of the engine.
-Nate

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'82 240D, 4-speed, 617 turbo engine