BMW M57 problems and how to fix them

Which M57 you have decides which faults you have

BMW built the M57 for fifteen years in four distinguishable generations, and a fault list that does not say which generation it applies to is worth nothing. Before you read any further, find the engine code. It is the number that matters; the family name is not.

The quickest paper check is capacity. The first M57D30 is 2,926 cc. Every later 3.0 litre M57 is 2,993 cc. If a listing says 2,993 cc it is not an original-generation engine, whatever else the advert claims.

The full code-to-chassis table, with capacities, outputs and years for every variant, is the subject of its own guide.

• Which BMWs have the M57 engine?

1. Inlet-manifold swirl flaps

Swirl flaps are small butterflies, one per inlet port, carried on a common shaft in the inlet manifold and driven by a single actuator motor and rod. They close at low load to spin the incoming air harder, which improves combustion and lowers emissions when the engine is barely working. They do nothing useful at full load and nothing at all once the engine is out of the car it came from.

The failure is mechanical and well known across BMW's M47 and M57 diesels of this era: a flap or its spindle works loose, the flap goes down an inlet port, and an emissions device becomes piston, valve and cylinder-head damage. That is the whole reason the fault has a reputation out of proportion to the part.

Which engines have them is a question about the manifold, not about the model year. Aftermarket suppliers list delete kits across the M47, M47TU, M57 and M57TU range and are open about the fact that no clean year cut-off exists. Take the manifold off and look.

The fix

Remove the flaps and blank the holes they leave. Delete kits are sold in two sizes, 22 mm and 33 mm, and are chosen by the spacing of the flap fixing screws on your manifold — 35 mm spacing takes the 22 mm kit, 45 mm takes the 33 mm. Measure the manifold in front of you; do not order from the model year.

On a conversion this is close to free work, because the inlet manifold comes off anyway while the engine is on a stand and out of the vehicle. It is the one job on this page that is genuinely cheaper to do pre-emptively. If you are running one of our ECU packages, tell us what has been taken off the inlet side before we specify it.

2. EGR valve and cooler coking

The EGR system feeds measured exhaust gas back into the inlet to lower combustion temperature and NOx. Soot in that gas meets oil mist from the crankcase breather, and the mixture bakes onto the EGR valve, the inside of the cooler and the manifold runners. Over years of short, low-load journeys the passages narrow and the valve stops seating.

What the driver sees is rough running, a flat spot, inconsistent boost, limp mode, and EGR or mass-airflow fault codes that come back after being cleared. Every M57 generation is affected; how badly depends entirely on the duty cycle the engine had.

The fix

In a car that has to pass an emissions test, the job is to clean or replace the valve and the cooler and to clean the manifold while it is off — which is the same strip-down as the swirl flaps, so the two are one job rather than two.

In a conversion the engine runs on a standalone ECU rather than the donor car's, and the EGR system normally comes out with the rest of the donor's emissions hardware. Our Ford Transit M57 conversion kit, for example, is supplied with an ECU and standalone loom with DPF and EGR off, so the mapping matches the hardware that is actually on the engine.

• Ford Transit M57 conversion kit
• Kits de conversión M57 para Ford Transit

3. Timing chain and guides on the M57TU2

The M57's timing chain runs at the front of the engine. That is not a footnote: it is the single biggest practical advantage the M57 has over the later N57 for a conversion, because the chain can be reached without separating the engine from the gearbox.

On the late M57TU2 the chain, its guides and its tensioner are nevertheless a wear item, and reaching them is expensive in a complete vehicle. The warning is a rattle on cold start that fades as oil pressure comes up, and timing-correlation fault codes between the crankshaft and camshaft sensors.

The fix

Replace the chain, the guides and the tensioner as a set. Replacing the chain alone into worn guides is the version of this job that gets done twice.

We publish no mileage interval for it, because BMW does not treat it as a scheduled item and the honest answer depends on an oil history that a used engine does not come with. What we will say is when to do it: while the engine is out of the vehicle, before it goes behind a gearbox you have just paid for. If the engine is already on your bench and you are undecided, that is the moment the chain is cheapest it will ever be.

The alternative is to take the question off the table. A zero-mileage long block has no chain history to investigate, which is most of why builders buy one — when the finished conversion then misbehaves, you are debugging your own fuelling and wiring rather than wondering about the bottom end.

• Brand new BMW M57N 306D4 twin-turbo engine
• Brand new BMW M57D30TU2 306D5 engine

4. Variable twin-turbo actuators on the 535d and 335d

The twin-turbo M57s — the 306D4 of the 2004 to 2007 535d and 635d, and the 306D5 that replaced it — do not use one turbocharger. They use two of different sizes in sequence, with a control linkage and actuators that hand boost from the small one to the large one as load rises. That is where the extra power over the single-turbo engines comes from, and it is also where the extra complexity comes from.

Soot and heat are hard on linkages. Actuators and the control rod stiffen, then stick; boost stops following the ECU's demand, and the engine falls into limp mode with boost-deviation codes. The single-turbo 306D1, 306D2 and 306D3 engines have none of this mechanism and none of this failure.

The fix

Free off or replace the actuator and the linkage, and check the vacuum side that drives it before condemning the turbochargers themselves. The turbos usually turn out to be fine; what has failed is the thing that was supposed to move them.

For a conversion the choice is a real one. If you want the simplest possible boost control, buy a single-turbo donor. If you want 272 PS and 560 Nm, or 286 PS, the twin-turbo engine is the only way to get it — and a brand-new long block has no hours on its actuators at all.

Two more problems that only exist in a conversion

Neither of these is a fault. They are properties of the engine that become problems the moment it leaves the car it was designed for, and they are what a kit exists to solve.

• It is a long, heavy cast-iron straight six. Where it sits decides whether the gearbox and the driveline end up in line, and that measurement is what a Defender engine conversion most often gets wrong. Machined brackets exist so the engine can only go in one place.
• It will not run at all outside its donor car. It needs its own engine ECU, a correctly built loom, and an answer to the donor's immobiliser. This is the part that strands a home build for weeks, and it is the part that is in the box.

That is also the honest reason the four faults above are worth fixing during the swap rather than later: the engine is already out, already on a stand, and already stripped far enough that three of the four jobs are hours rather than days.

• BMW M57 engine mounts for the Land Rover Defender
• BMW 6HP and 8HP to LT230 transfer case adapter
• Land Rover Defender M57 kit with the ZF 8HP
• Land Rover Defender M57 kit with the ZF 6HP

What we would start from

If you ask us which donor to buy, the answer depends on the gearbox you intend to run and on how much power the rest of the vehicle can absorb — and we will give it to you properly rather than in a sentence. What we will not do is pretend the M57 has no weak points. A vendor who cannot name them has not had enough of them on the bench.

Send the platform, the gearbox and how the vehicle is used. We will say which variant we would buy, what we would do to it before it goes in, and which of the four faults above is already handled by the kit.