BMW Turbo

BMW Turbos: reliable N47 engines, hard-worked N57 engines — two very different realities at replacement

Across the BMW diesel fleet, the N47 family (2.0d, codes N47D20, N47D20A, N47D20C, N47D20D, N47D20O1) has a well-documented structural weakness in the timing chain, yet its variable-geometry turbo generally handles the load well — provided the engine oil is clean and changed on time. The N57 family (6-cylinder, codes N57D30, N57D30B, N57 D30 B), fitted to the 330d, 535d, 730d, xDrive40d and X5 35d, operates under significantly higher boost pressures: the CHRA bearings and variable-geometry actuator wear more quickly, especially under intensive motorway use or following episodes of overheating. The classic symptoms — blue-grey smoke under acceleration, a high-pitched whistle at mid-range revs, progressive power loss or limp-home mode — often point to a turbo at the end of its life, but can equally indicate an intake hose sealing issue or a blocked EGR circuit and DPF. Replacing the turbo without addressing the root cause will invariably lead to a rapid recurrence.

Identification: N47, B47, N20, N57 — don't mix up the generations

BMW's gradual transition from the N47 to the B47D20A (then B46B20, B48B20A, B48B20B) on recent Série 1, Série 2, Série 3 and X1 models, and from the N20/N26 to the B48 on 4-cylinder petrol variants (335i, 640i, Z4), creates genuine overlap zones across model years. Two vehicles sharing the same commercial designation — for example the 318d or 320d — can carry turbos with entirely different manufacturer references depending on the year of manufacture and the engine code stamped on the block. The engine code is the only reliable reference point here: BMW references beginning with 11657… or 11658… are not interchangeable between families, and several suffixes (e.g. 7795498A01, 7795498B01… through to K10) correspond to successive revisions of the same N47 turbo. On N57 6-cylinder blocks, the presence of sequential twin turbos on certain variants (xDrive40d 313 hp, 535d) means you must establish whether it is the low-pressure or high-pressure turbo that has failed before placing any order.

New or reconditioned: what this page covers

The collection covers the full range of BMW models from the Série 1 to the Série 7, as well as the X1, X2, X3, X4, X5, X6, Z4 and M5, in both diesel and petrol variants. Depending on the reference, the turbo is available new (direct sale, no unit to return) or as a reconditioned exchange unit. Before fitting, it is essential to flush the oil circuit, replace the turbo gasket and check for any foreign bodies in the intake manifold — a particularly critical precaution on N47 engines, where timing chain failure may have generated metal debris.