BMW F01 7 Series: 730d, 740i and 750i

Picture cruising down the Southern Motorway in two tonnes of German executive refinement, the N57D30A straight six pulling cleanly from low revs, the air suspension ironing out every bump in the road. That is the 730d at its best. What it does less effortlessly, somewhere around the 100,000 kilometre mark, is quietly develop a handful of faults it was essentially born with. The N57D30A is a 2993cc inline six producing 245 hp and 520 Nm of torque, backed by a Bosch EDC17 ECU. It is a sophisticated piece of engineering, and sophisticated means expensive when things go wrong.

The diesel 7 is the entry point to the F01 range in terms of purchase price, and that makes it the most common one we see. It is also the one where deferred maintenance does the most damage, because the faults compound each other in a way the petrol variants do not quite match.

The swirl flap issue deserves a special mention. When these plastic flaps fail, fragments can enter the engine. It is one of the few situations on a modern BMW where doing nothing is genuinely dangerous rather than just inconvenient. If yours has not been inspected and the flaps have not been addressed, that needs to happen before anything else.

The timing chain sits at the rear of the engine on the N57, which is the opposite end from most engines. Getting to it is a substantial amount of labour, so catching chain wear early through proper diagnostics, rather than waiting for the rattle you can hear from outside the car, makes a real difference to the final invoice.

The 740i is arguably the most balanced F01. Six cylinders rather than eight means a lighter nose, slightly less complexity, and a purchase price that sits comfortably below the 750i. The N55B30A is a 2979cc single turbo inline six producing 326 hp and 450 Nm, managed by either a Bosch MEVD17.2.6 or a Siemens MSD87 ECU depending on build date. It is a strong engine when it is healthy, and a source of real frustration when it is not.

Compared to the 730d, the 740i is a step up in everyday response. Compared to the 750i, it is meaningfully simpler under the bonnet. If you are buying used and trying to decide between the three, the 740i often gives you the most usable day to day car once it is sorted, especially if most of your driving is in town rather than long highway runs.

The electric water pump is the fault we see most on the N55 in this car. Unlike a mechanical pump, it gives very little warning before it fails. When it does, the engine can overheat quickly and quietly. Replacing the pump and thermostat together makes sense because the labour overlap is significant and the thermostat housing on these fails at similar mileages.

Carbon build up is an unavoidable consequence of direct injection. Fuel never washes the backs of the intake valves the way a port injected engine does, so carbon accumulates over time. The fix is walnut blasting, which we carry out in house. It restores idle quality, throttle response and fuel economy, and it is noticeably cheaper than chasing misfire codes with parts you may not need.

The 750i is what happens when BMW decides to build a proper flagship and does not hold back. A 4395cc twin turbo V8 producing 407 hp and 600 Nm, managed by a Siemens MSD85 ECU. Merging onto the motorway in one of these is a properly memorable experience. But the N63B44O0 has a reputation, and that reputation is well earned. BMW even ran a customer care programme for known oil consumption issues on this engine. That tells you everything you need to know about how significant the faults are.

The N63 architecture puts the turbochargers inside the vee of the engine rather than on the outside. This is brilliant for packaging and throttle response, and genuinely problematic for heat management. The valley between the cylinder banks runs extremely hot, and that heat does real damage to seals and components over time.

If you are looking at a used 750i and the service history shows inconsistent oil change intervals or the oil level has never been checked between services, walk away or budget for a full engine assessment before you commit. The valve stem seal job on an N63 is not a quick afternoon of work, and if the timing chain guides have been running on degraded oil, you may be looking at a chain replacement too.

On a properly maintained example though, the 750i is exactly what BMW intended: effortlessly fast, supremely comfortable, and genuinely impressive well over a decade after it left the factory. The key is knowing what to look for and staying ahead of it.