The connecting rod and main bearings run out, and the cause is the factory oil pump: it is undersized and does not deliver enough oil volume at idle and at low revs. BMW specifies 1.2 bar of oil pressure at idle at operating temperature, but on engines with mileage it falls below that, and the bearing shell is no longer adequately lubricated with that much. Bearing damage is reported between 130 000 and 200 000 kilometres, but it is always preceded by a longer period with low oil pressure.

The most important thing to know is that the control unit does not signal this: no lamp comes on for low oil pressure, and no fault code is stored either. The symptom is a quiet ticking at idle and a metallic noise under load, and at the rod bearing this is often explained by something else. It can be measured, though: a workshop connects a gauge and reads the real pressure at idle at operating temperature, and below 1.2 bar the engine is running in the period that causes the damage.

The length of the oil change decides matters on this engine. A change between 10 000 and 20 000 kilometres protects the bearing, the long factory interval does not. If the main bearing turns, the crankshaft is damaged too, and the upper half of the main bearing bed is aluminium while the lower is steel, so repairing the crankcase is difficult, and the block often goes out cracked and beyond repair. As prevention an uprated oil pump exists, with larger gears and its own pressure regulator, between 800 and 1150 euros, without fitting.