While diesel engines are usually made from steel to withstand the higher peak cylinder pressures, that is not true of these models. BMW is using an alloy block for the diesel engine.

The extra weight is likely related to ancillary equipment (diesel heaters if so equipped, heavier battery, heavier starter motor).

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue