How old is the battery? If you dont know or its over 4 years old, replace it. Diesels must crank over at a reasonably fast rate to start, unlike a gas engine. Jump starting a car never "charges" a battery. On a diesel, once started, a battery is not even necc except to have voltage ready to restart it. My gut feeling is the battery was weak, the engine was extremely cold and those 2 things kept it from starting. If you would feel better, have the battery slow charged overnight out of the car and load test it after fully charged. If it passes the load test, consider yourself lucky, if it failed, buy another.

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.