Seems that BMW & reliable don't do together. At least that's what I can gather from owners.
I think that's the general opinion of many gasser BMW owners. Also note that most BMW owners rely totally on their dealer for all service work. Most BMW owners never lift the hood on their cars. This is unlike many TDI enthusiasts here who choose to DIY due incompetent VW dealer service and also like to work on their cars. Many BMW owners also like to throw perfectly good cars away and get into another new one as soon as the original factory warranty and free maintenance ends. It's not that there is anything wrong with the cars and they are VERY solidly built, probably more so than VW. BMW has a different type of clientele compared VW TDI enthusiasts like us who care about our cars and choose to keep them long term. I am not your typical BMW owner who is into the "new every 2" cycle.
Even though I don't own TDIs anymore, I'm still active here and support TDIclub because this is where it all started for me. I still buy from TDIclub vendors because they also have what I need to maintain my diesel BMWs. Gasser BMWs weren't a consideration at all when I went BMW-shopping.
BMW's 6-cylinder engines are very solid and reliable engines from what I've gathered. OTOH, BMW's V8 gassers have been another story. IIRC, the N63 engine is known to be an oil drinker and there's currently an open campaign to correct some known timing chain issues. Also FWIW all BMWs diesel and gasser engines use a timing chain instead of a belt. I'm not aware of BMW using a timing belt in anything.
The way I see it however is they are more needy then a Honda and require prompt service on the expected mileage intervals. I'm fine with that since I've been doing just that with my vw tdi and haven't had any problems yet. *knock on wood*.
As for BMWs being "high maintenance", I've found that to be not the case so far with mine. I'll let you know in another 200k miles.
But let me get to the thread's title. How reliable are the bmw diesels?
I'm only at 56k miles on my 2014
535d xDrive sedan and it's still way too early to tell.
Ordered the car on 7/1/2013, took delivery on 8/14/2013, probably among the first batch of them in the country. Zero problems so far other than I had to have the lens on the FLIR night vision camera replaced after taking a rock hit and allowing water entry into the camera system.
I'm only at 100k miles on my 2012
X5 35d and it's also still way to early to tell. I bought the X5 used (CPO deal) at 52k miles in March 2014 and it is serving me very well. From the build date the car was less than 2 years old when I bought it and at 52k miles it suggests the original owner did mostly highway miles like I do. Basically the original owner threw a perfectly good car away as soon as the original factory warranty and free maintenance ended. I've had one hiccup where 3 sensors mysteriously failed at the same time and they were covered under CPO warranty. The only other thing was the right fog lamp had to be replaced due it taking a rock hit and breaking the lens and allowing water entry which then took out the bulb.
So I'd be really curious to hear from actual owners of these cars. (Both 4 & 6 cylinder)
Any major problems you encounter?
Any 2nd hand things that you've seen from other bmw owners?
Any common issues to watch out for?
Major problems? Still way too early to tell.
2nd hand things? Intake clogging aka Carbon buildup (CBU) has occurred in 335d and in a few others. Most often it happens due to the same factors that lead to intake clogging in TDIs. Most cases have been due to using the car exclusively for short trips and always babying the car instead of driving it like it was stolen w/cops in hot pursuit.
Common issues? CBU in the 335d and sensor failures in the exhaust system components. A few 335d and X5 35d cars have had urea tank heater failures. The general pattern of known issues is similar to known TDI issues.
My BMW diesels have been serving me well. Now that I'm into BMW diesels it's hard for me to want to go back to another VW.
Good luck.