Originally Posted by JCL

There isn't any public high-mileage experience with the most recent BMW diesels since they are fairly recent introductions. Assuming that there are no problems with the aluminum blocks, they should have good life, similar to previous generations of BMW diesels.

Older-technology heavy-duty diesels that routinely went for hundreds of thousands of miles bear little resemblance to today's electronic/aluminum block diesels.

In general, diesels have higher compression ratios, resulting in higher peak cylinder pressures, which are a factor in faster wear. That can be overcome with a heavier block casting, but we are not seeing heavy blocks in modern automotive diesels. Diesels benefit from lower piston speeds, which is a factor in lower wear, due to their lower relative speeds compared to gasoline engines. Both these factors are theoretical to a certain extent.

In practice, considering the complexity of the rest of the vehicle, the car is likely to become very expensive to maintain long before the cylinders wear out, exactly the same as with a gasoline engine.

Maintenance cost? High pressure direct injection fuel systems are very similar these days for gasoline and diesel. Diesels have no ignition system, but how much do we really spend on spark plugs these days? Diesels will be less tolerant of water in the fuel, or of cold weather, and will likely require urea to be added during services, but all in, maintenance costs are likely to be pretty much a wash.