BMW M47

BMW's 2.0 four-cylinder diesel before the N47 — in the E46 and E90 3 Series, the E39 and E60 5 Series, the E87 1 Series and the E83 X3.

Its signature fault is the swirl flaps, and it is the one that destroys engines. The intake manifold carries small pivoting flaps to shape airflow at low speed. Their retaining screws work loose, a flap is drawn into a cylinder, and the engine is finished. On a car with unknown history the state of the flaps is the first thing to establish, and many have been removed and blanked by previous owners — which is a modification worth confirming rather than assuming, because a half-done deletion leaves debris behind.

Its timing chain is at the gearbox end of the engine, the layout that made the N47 notorious. The M47 suffers it less often but the geometry is the same: a chain job means the gearbox comes out, so a rattle at start-up is an expensive noise on this engine rather than an ordinary one.

The rest is the diesel duty cycle — EGR clogging, glow plugs, and on later cars a particulate filter that cannot regenerate on short journeys.