Lucky me, my 300D fired right up at 3F this morning. First rotation, like normal.

What type and weight of oil do you have in there? For extreme winter use and outside storage, I'd use at least 10W30, maybe even 0W40 synthetic for the winter. Cranks MUCH faster than dino oil (the 0W40 pours like water at 35F).

Change back to the normal 15W50 in the spring.

If the oil is OK, your choices narrow:

Block heater if possible -- saves wear and tear on engine and starter.

New battery, make sure the cables are good on both ends.

Check starter and starting speed -- MB starters are known for getting high resisitance windings and running slow with very high current draw, can only be fixed with a new armature.

Valve adjustment on pre-603 engines. You ain't gonna start with slow cranking speed and low compression....

Some MB diesels just won't start without a block heater at 0F -- my brother's

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!