[Kernel Kurtz]

I remember when I factory ordered my '11 335i, they had just switched from the N54 to the N55 and many enthusiasts were upset thinking the N55 would never be as good. Seems it actually turned out pretty well in the end.

[babyray]

I’ve had the N54, N55, and B58. The N54 was a pain in the arse. Oil leaks, crummy injectors, hpfp, wastegate rattle, you name it it happened. I drove it to over 130,000 miles and would still be driving it if not for a deer ending it. N55 was great. No issues. Keep the oil changed in though. Weak charge pipe and intercooler need to be upgraded. B58 so far no issues, tune and go.

[mecheng77]

Originally Posted by Nickies

Is there any report of timing chain failure on the B58? This seems to be terribly expensive to service.

I haven’t heard of any

[msej449]

The top two weaknesses of the N55 are the turbo inlet charge pipe and the coolant overflow pipe. The charge pipe is under-engineered and prone to vibration stress and eventual fracture. The coolant overflow pipe tends to snap at one or other end. Long term owners will generally replace both, but the charge pipe is non-trivial, as it’s somewhat buried behind other components. The overflow pipe is cheap and easy to replace, and many owners DIY that and do a coolant refresh at the same time. Most long-term owners will also do an engine oil replacement every 10K miles, rather than the service schedule’s 20K. Beyond that, above the service schedule items, people will replace the ZF auto oil around 50-60K even ‘though BMW says it’s ‘lifetime’, contrary to ZF’s service recommendation. The N55 models like the M235i had an option to retro-fit a BMW MPerformance limited slip differential (LSD), sourced from Drexler. They recommend an oil change around 30-40K but again, BMW says this is ‘lifetime’. So for example, an N55 M235i is best bought before 40K or so miles, when your main concern is whether it’s had the 10K oil changes, and where you can undertake the other preventive maintenance work if you plan to keep it for any length of time. But if you do, then you need to budget for them.

This isn’t meant to paint the N55 based cars as particularly prone to mechanical problems. All cars have some components with MTBFs that are shorter than others. I’ve not owned a B58, and it’s a newer engine design, so I’ve no ownership experience of it and it’s not been out there as long.

[mecheng77]

Originally Posted by msej449

The top two weaknesses of the N55 are the turbo inlet charge pipe and the coolant overflow pipe. The charge pipe is under-engineered and prone to vibration stress. The coolant overflow pipe tends to snap at one or other end. Long term owners will generally replace both, but the charge pipe is non-trivial, as it’s somewhat buried behind other components. The overflow pipe is cheap and easy to replace, and many owners DIY that and do a coolant refresh at the same time. Most long-term owners will also do an engine oil replacement every 10K miles, rather than the service schedule’s 20K. Beyond that, above the service schedule items, people will replace the ZF auto oil around 50-60K even ‘though BMW says it’s ‘lifetime’, contrary to ZF’s service recommendation. The N55 models like the M235i had an option to retro-fit a BMW MPerformance limited slip differential (LSD), sourced from Drexler. They recommend an oil change around 30-40K but again, BMW says this is ‘lifetime’. So for example, an N55 M235i is best bought before 40K or so miles, when your main concern is whether it’s had the 10K oil changes, and where you can undertake the other preventive maintenance work if you plan to keep it for any length of time. But if you do, then you need to budget for them.

This isn’t meant to paint the N55 based cars as particularly prone to mechanical problems. All cars have some components with MTBFs that are shorter than others. I’ve not owned a B58, and it’s a newer engine design, so I’ve no ownership experience of it and it’s not been out there as long.

Correct, the coolant pipe is a 10min job taking your time, and including the prime

The charge pipe is like a 2-3hr job

[XutvJet]

Originally Posted by msej449

Most long-term owners will also do an engine oil replacement every 10K miles, rather than the service schedule’s 20K.

Maybe things are different in Europe, but in the US, BMW's recommended oil change schedule is once a year or 10K miles. 20K miles would be BONKERS!

I've done 3 used oil analyses on my M235 over the years and have learned that the OW-30 BMW LL01 oil, while robust, starts falling out of grade by around 7500 miles. Thus, I would not extend oil any longer than that, especially if the car is tuned. Most every independent shop and BMW tech will tell you to change the oil on a turbo BMW may more often than at 10K miles.