[MrJE]

So, after reading a lot about the 3 series, I have decided that a 320(preferably diesel automatic) is what would suit my needs and wallet most.
Now, I have read a lot about the car, but still have a few questions that I really haven't found any good answers on.
So I am very, very thankful if you could try to help me

1. The cars I'm looking at has often rolled around 150-200' (maybe even 250k)kilometers. Assuming I make sure it has a fully stamped service book, should I worry about some major problems/expenses that may pop up(maybe due to age/distance travelled?)

2. I know that BMW can be expensive to service, but how often should I be prepared to drive it to mechanic? Every 20' kilometers?

3. The automatic transmission. Should I be aware of any know problems? Or should I even stick to manual?

4. Diesel or not? I am guessing yes, but never hurts to ask.

Looks like an awesome car so I am really hoping that nothing crazy will show up. Thank you in advance!

Edit: and of course I may have forgotten something, so feel free to give your impressions of the car if you would like

[RobertRO]

I think you should take some time and read through the BMW forums on the timing chain issue that seems to have been plaguing the BMW N47 engine since its early days - and it's still not fully solved by BMW.

As I understand, due to a design glitch, on a small percentage of N47 engines the timing chain broke, with the consequences I guess you figure out. Besides the engines lost due to timing chain failure, there seems to be a considerable number of N47 engines whose owners complained about an unhealthy noise from timing area of the engine. It turned out to be the tell-tale sign of a worn timing chain. The fix - in some cases partially covered by BMW, but in most cases fully on owners' expense - was the replacement of crankshaft (!), timing chain and small related parts. The crankshaft had to be replaced because the timing chain sprocket is integral, not removable - a stupid design.

I expect that the N47 engines with high mileage (over 200k Km) may be more prone to timing chain failures.

As I said, you must document yourself on this matter. I am just pointing out that it exists, but I haven't looked deep into it, as the N47 engine is not of any interest for me - at least not now.

Bottom line, it may be that an early E9x 320d with the M47 4 cylinder Diesel engine, or better any E9x 325d/330d/335d with the M57 or N57 6 cylinder Diesel engine are preferred to the N47 engine - that is if you really want a Diesel E9x.

[Vervain]

I'm definitely no expert, but all the buying advice that I've received was to stay away from high-mileage turbo-diesels.

I'm being no help to you, sorry.

[MrJE]

I had not thought about the N47 problems but after reading up on them now I am thinking about going for the 320i with n46 engine. I have heard about the problems with the oil leakage on that one but I guess it is more reliable than the N47 at least?

[RobertRO]

Originally Posted by MrJE

I had not thought about the N47 problems but after reading up on them now I am thinking about going for the 320i with n46 engine. I have heard about the problems with the oil leakage on that one but I guess it is more reliable than the N47 at least?

There's no absolute truth, and there's no perfect reliability, when we are talking about BMW.

The N46 engine is quite low in terms of desirability. Besides its considerable share of problems, I would say that the power is rather disappointing, and the fuel consumption rather high for its performance.
Frankly, when you're looking for low to medium displacement (up to 3 liter), decent economy and good reliability modern BMW engine, you don't have too many options.
No engine is perfect, but my opinion is that M54 and N52 gasoline engines (both with 6 cylinders), or M57 (6 cylinders) and M47 (4 cylinders) Diesel engines have shown an adequate reliability history.
If you want a newer model, then the N20 (4 cylinders) and N55 (6 cylinders) gasoline turbo engines may be a good choice - but keep in mind that the N20 is still rather new.

I would advise for a lower mileage, lower end BMW, preferable with some warranty left, instead of a high mileage, higher end BMW.
A full and verifiable history of the car is very important.

The amazing build quality of E28 / E32 / E30 chassis, and superb reliability of M30 / M50 / M10 / M20 engines are a distant past.
A modern second hand BMW can easily turn into a money pit, unless you are mechanically inclined and capable to do yourself most of the servicing. Even then, modern BMWs require lots of "special tools" which drastically restrict your chance to fix yourself some issues.

I don't want to sound too negative and advise you against buying a BMW. I just want to warn you that you must read a lot and have a number of test drives before you decide which BMW to spend your money on.