BMW 3 Series 320d Turbo

M47 or N47: two engine families, two different turbos on the 320d

On the BMW Série 3 320d, the engine code is the first filter to apply before searching for a turbo. The 320d has spanned several generations with two radically different engine families, and a turbo designed for one will not fit the other. The M47 D20 (204D4) is fitted to E46 bodystyles — the 320d saloon, 320Cd coupé and 320td compact — and represents the oldest generation within this range. The M47 D20 without suffix came next, followed by the updated variants M47N2 and M47TU2 on the 150 hp and 163 hp versions. These are still M47 engines, but with turbos that do not share the same references.

N47D20A and N47D20C: the break with the next generation

From the introduction of the N47 engine, the 320d moved into a new technical generation. The codes N47D20A and N47D20C cover the 163 hp and 184 hp versions. Both codes also appear under the 163 hp / 177 hp output in the listing, which means that a single code can correspond to different power levels depending on the configuration: the power figure shown on the spec sheet is not enough to identify the correct turbo. Only the code stamped on the engine block is definitive. On N47 engines, the turbo features variable geometry with an actuator; actuator fouling or a fault in the variable-geometry control are common causes of performance loss before outright failure.

Symptoms and causes to identify before replacement

On both M47 and N47 engines, the common symptoms of a failing turbo are an abnormal whistling noise under acceleration, blue or black exhaust smoke, and sluggish power delivery. The most frequent cause remains insufficient lubrication: degraded oil, a partially blocked oil feed pipe, or too long a delay before oil pressure builds after start-up. On older-generation M47 engines, fouling of the intake circuit caused by the EGR system can also deposit residue in the compressor. Fitting a new turbo without addressing the root cause will lead to another failure. All turbos listed here are sold new, as a straightforward sale.