I wrote this a few months ago. I hope its useful.
Absolutely fantastic cars but then I would say that - I have no problems admitting that I am a blinkered E39 fanboy. But only since I got mine, and I only got mine becuase it really is noticeably better than any similar car of the same sort of age. Now thats out of the way...
.... it will not be as bulletproof to run as your Impreza. Stuff WILL break. Some it it will be cheap and easy to fix, some of it will be less cheap and less easy to fix. It's unlikely to ever let you down but for some people throwing 300 quid here, 100 quid there at it might get a bit annoying. For me, well I'd rather pay to repair mine than pay for depreciation in a newer Vauxhall so I'm still dead happy.
I wrote a pretty comprehensive guide on what to look out for which I will attach to the bottom of this reply.
Firstly though - are you sure you want a 530d?
I drive both a 530d SE and my 530i Sport (Infact until I took the 530i on a 500 mile trip the other day I've probably covered more miles this year in the 530d, ironically) so if you've got any direct questions about the differences I should be able to provide you with a useful opinion. Interestingly fuel consumption report for that trip:
Exeter-Worcester, M5: 39.2mpg (Yes, 39.2mpg. I was so shocked I then brimmed the tank to check for accuracy of the fuel computer).
Worcester-Southampton (rush hour in Worcester, went a bit quicker on the way back to Soton) took the average down to 35.7mpg over a total of 280ish miles.
Southampton-Plymouth (Early evening, not much traffic, not driving for economy, plenty of overtaking but no silly speeds) averaged 31mpg.
The big thing with the two is you need to make sure the additional economy you get from a 530d will offset the considerable additional expense associated with buying one AND the potential additional failiure points such as the turbocharger and high pressure injectors. 530i's are often up to £2k cheaper than an otherwise identical 530d, and of course are ultimately faster cars.
Fuel economy wise...
Around town, short trips from cold:
530i 20-23mpg, 530d 28-31mpg
Mixed runs, blasts along single carriageway A roads, overtaking, etc etc
530i 28-31mpg, 530d 36-39mpg
Motorway work at 70ish
530i 37-40mpg, 530d 44-48mpg
And here follows the post I did the other month:
Ok, buying a 530i..
Firstly you've got to be really careful. The best way to buy a good value used BMW is to buy an absolutely immaculate example thats less than 5 years old from its original owner. Unfortunately as time goes by its more and more difficult to do this with the E39 so you need to be a tad more open minded.
These are excellent cars with absolutely fantastic build quality. In terms of build its probably the best BMW have managed and not since it was around, new, has BMW had a car on the market thats been so much better than the competition. This means that condition wise it's very easy to keep them looking very nice and the interior is very hard wearing. This has a few important consequences:
a) You can be fussy on condition - it shouldnt be 'in good condition for age' it should just be in good condition. There are 10 year old E39's out there which look like new inside. Mine is the wrong side of 150k miles and you cannot tell. This means you can, if you are fussy, get a really nice example
b) They are very easy to clock - you can take a 140k mile car, wind it back to 80k, and nobody will suspect a thing. This happens far more often than it should, I looked at at least two cars at auction with high miles which subsequently turned up on Autotrader a few weeks later with less miles on it. The usual 'look for worn out seat' etc etc advice doesnt apply becuase even after 100k miles the seats remain in good condition.
So, be very careful. Insist on Full BMW SH as a) it shows the owner hasn't been the sort to skimp on looking after the car and b) you can verify the history wtih BMW and thus verify the mileage is genuine. In theory if the car detects its been clocked (The mileage is stored in different places in the car) it brings up a red dot beside the mileage on the dashboard but there might be a way round this. Be careful.
c) You don't really need to worry about mileage unless you plan to resell it in a short period of time. This peice of advice becomes less relevant as the cars get older and get more owners as it's far more difficult to work out how the car has been used but I'll say it anyway. These are fundamentally very reliable cars which wear miles very well and are very capable of being in excelent condition pretty much regardless of mileage. Even the common failiure points on them seem to happen at a certain age rather than mileage (More on those later). Therefore, buy on age, condition and history first. Use mileage to negotiate the price.
So, what to look for. Personally, a car with as few owners as possible. Far too many E39's now have 900 owners all of whom have had varying opinions on how much money you need to spend on a car to keep it going. Remember, to most people, a car is worth to them what they paid for it until the day they trade it in. The more they've paid the more you'll hope they'll value the car and thus be prepared to spend to keep it running (There are of course exceptions to every rule but this is a good guide).
Personally, I'd want a one owner from new example but at the age of car you'll be looking at, 2 owners from new with the last owner having had it 2-3 years is probably more likely and thus more reasonable.
As far as the actual interior condition goes, the only areas of wear should be on the drivers side bolster of the Sport seat, and perhaps a little on the steernig wheel. Everything else, dashboard, buttons, gearstick, etc etc is very resiliant and should be showing little signs of wear.
For context, here are some photographs of what the interior of mine was like - 140k miles:
Really baggy seats, scratched leather, etc etc = hard life and/or abuse. Don't buy one from a fat guy as they tend to ruin the drivers seat.
Onto the exterior..
Again, very well put together. Perfect shutlines etc etc, if not, ask questions. Watch for rust. Yes, rust, on a BMW, but there we go. Two areas on the E39 - inside the fuel filler cap, and on the boot tailgate where it meets the bumper. Neither of this is structural, its purely cosmetic, but you can probably use it as a bargaining point all the same. If the car is under 6 years old it's both covered by the BMW Corrosion Warranty.
Wheels - on the 17 inch Sport wheels you do get little patches of corrosion under the laquer. The 18 inch wheels, by far the best, are Diamond Cut and if not cleaned on a regular basis can also suffer damage. Use the condition of these to judge how much the care has been cared for. Tyre sizes are different front and rear so make sure the owner hasn't cheaped out. For reference:
17: 235/45/17 front 255/40/17 rear
18: 235/40/18 front 265/35/18 rear
Rear tyres on the 18's are a bit expensive as it's a stupid tyre size thats shared only with the Porsche 911 C4. Grrr.
Driving...
If it doesn't feel right it probably isn't - the engine should be very smooth. It is here I will mention the E39's biggest bugbear. They are very sensitive to wheel balance and imperfections in the aluminium suspension setup (Be that allignment, worn bushes, etc etc) and this will tend to cause 'the dreaded shimmy' where you can feel a vibration through the entire car at speed. Do try not to accept any car with this shimmy unless you are certain why it has it, becuase it can be any of a number of things. Most common are wheel balance (Most tyre shops cant balance E39 wheels properly becuase they are monkeys) or warn upper/lower control arm bushings.
It will not feel that fast, despite the fact 0-60 will come up in 6.7 seconds and it'll hit 100 in just over 17 seconds, becuase the car is very refined and most of the engine noise etc doesn't make it into the cabin. This is a shame, as it robs the car of the thrill of acceleration, but a quick check of the speedo will remind you that actually, you are going quite quick. Top speed is limited to 155mph but without this limiter the 530i has been known to hit speeds of 156, perhaps even 156.5mph
So what goes wrong and how much is it going to cost you to run?
Well so far my list of things that can and do break is thus:
a) Shimmy. As described above. If its bushes, £250 a side should see it right.
b) COOLING SYSTEM
The cooling system in the E39 5 Series is crap. Not in the efficiency sense, but in the reliability and longevity sense. It WILL fail, usually when the car is between 5 and 7 years old seemingly regardless of mileage. The OEM radiator has a design fault which leads to it splitting at the plastic end tanks and ****ing cooling all over your engine bay. If it doesn't fail like that, then the plastic header tank will split. On the cars you are looking at for this sort of money if it hasn't had a replacement cooling system it's almost certainly going to need one during your ownership.
Replace the lot at once - waterpump, radiator, header tank, upper/lower hoses (May as well) and the thermostat. Budget about £400-£600 for this work.
I hate the cooling system, it is truely the only nightmare I have had with my car. And so has EVERY other 530i owner I know, without fail. But once its replaced you should be ok.
Oh and the header tank is black, so you can't check the level of coolant if the engine is warm. GOD DAMNIT.
c) Propshaft
Most people ignore this. I got a whole new Propshaft out of BMW for it. It's usually just a bearing. The centre bearing or propshaft donut can wear out. You will hear a 'chink' nose as you apply power from 1st or 2nd gear. An indy can fix this for less than 200 quid. Or you can ignore it like Olly has.
d) Climate Control system
The most common failiure here is the Final Stage Resistor, or 'Hedgehog' (Its got a huge heatsink on it that spikey). It fails and your climate control goes bonkers, randomly adjusting blower speed and doing even more impressive things like leaving your internal blower on all night and flatening your battery. A new one is 50 quid, takes 20 minutes to fit, but it can be a bit awkward. If you've got no blower at all its your blower motor, these require the dashboard to come out. This one just cost me 320 quid at BMW.
e) Automatic gearbox
These can fail but I've no idea how common it is. Half the internet reckons its becuase you didnt change the sealed for life gearbox fluid at 100k miles. The other half the internet reckons it's something else or becuase you DID change the gearbox fluid at 100k miles. I don't care as autoboxes are for old people. A new box is a large amount of money.
I can't think of much else off the top of my head, will add later if I do.
So aside from stuff breaking how much will it cost you to run?
Servicing is on a variable system with 15,000 miles as a base. Use it around town/thrash it, and it'll be less. Sit on the Motorway and it'll be more. The servicing order, and prices, are as follows:
Oil Service - £80-170 depending on where you go. You can get them done by BMW for about 130-140 quid including oil if you've got a decent dealer.
Inspection 1 - £200-£300.
Oil Service
Inspection 2 - £270-£400
Oil Service
Inspection 1
Oil Service... etc. You get the idea.
You also need brake fluid every 2 years @ £30-£80 and Coolant every 4 years at about the same cost.
Tyres - a full set of decent tyres for the 17 inch wheels will set you back about £450 or £550 for the 18's. If you are a cheapskate ***** you can buy crappy Kumho's or something for less but if you are a cheapskate ***** please buy a different car, thanks <3
Insurance - is Group 17 but suprisingly reasonable.
Tax - is loads. If its a Y reg or newer it will be affected by the governments utterly retarded taxation system. The manual will cost £415 a year to tax, and the automatic £430 a year to tax.
Fuel consumption. If your name is Olly and you have steel toecap boots you will get 19.2mpg. If your me and you find the Ken Bruce show on Radio 2 really rather thrilling you'll get 39.2mpg. If you are a normal person living in the real world you'll see 30-35mpg on a trip, 18-23mpg around town, and something in the middle in general driving. It takes Super Unleaded.
Bad points?
a) It's too refined. It robs you of the excitement you get from accelerating quickly yet still gets you into license loosing territory far too quickly without you realising
b) The stereo is so awful it's beyond rubbish.
c) Muppets keep buying them and fitting fake shark fins on the roof and stupid 19 inch wheels.
Thats about that really. They do cost rather a lot to run - but personally I think its worth every penny. I absolutely love mine and despite test driving loads of other stuff I've yet to drive a single car which makes me think 'I need this over my E39'. It's the perfect blend of performance, economy, long distance ability, A road handling, good looks without standing out, etc etc. And it even looks like an M5, with factory fit M badges everywhere to suit people like me who really want an M5 but cannot afford one.
Brilliant cars. Just don't buy a bad one, or buy a good one and ruin it with crap replica wheels.