The 8-Series is BMW's forgotten supercar. Most people, even some BMW fans surprisingly, don't even know there was an 8-Series back in the 90's!
The first car that was released in this category, the BMW 850i (with its heavy V12 engine) has given the 8-Series pretty much a bad rap, and the 850i (or 850Ci) is basically the very car that people (who know of this car) first think of when you mention the 8-Series to them.
So, why the bad rap? Well, the 850i was HEAVY (weighing 2 tonnes), and driving performance suffered because of this. In fact, after 3 years, BMW withdrew it from the market because sales were so dismal. They did release a much better version of the V12 in limited numbers; the 850CSi, but that's another story.
So, from mid-1993, BMW went with a V8 version called the 840Ci. Now that the car was 200kg lighter, things started looking up. It was cheaper, didn't have two of everything to replace under the bonnet (like the heavier V12), and had a totally different ride and handling experience for the driver. Sales were suddenly better, so much so that it was continued in production right up until 1999.
Strangely enough, there was only around 40hp difference between the V12 and the V8, so people were flocking to the much cheaper, and nearly as powerful, V8. The V8 versions were also much easier to work on and maintain.
The first engine in the 840Ci from 1993 to 1995 (an M60B40 V8), was very reliable - some would consider almost bulletproof - compared to the second engine that followed from 1996 until 1999; the M62B44. The M62B44 engine had something called VANOS, which became a very expensive issue to fix if problems developed, whereas the M60B40 did not have this, so early 840Ci owners didn't have to worry about this at all.
The 840Ci's with the M60 engine had a 5-speed automatic gearbox, with 3 selectable modes: Economy, Sport, and Snow. The M62 versions however, had a Steptronic Transmission, where you could move the gear selector to the side to manually choose when you wanted to change gear.
What to look for in an 8-Series.
Engine: Go for the more reliable M60 4.0 litre engine (instead of the problematic VANOS M62 4.4-litre). The M62 versions did have a Steptronic Transmission, but if you can live without that and the VANOS, the M60 is your better option.
If you can live without the M62 version with the Steptronic Transmission, the M60 with the straight 5-speed automatic is your better option.
There can be some issues with wiring getting brittle after so many years before eventually snapping in the boot, so look for a car that has had these issues fixed. A lot of other issues, in some cases, can sometimes be fixed just by replacing Relays.
After 120,000kms, things will need replacing. LOTS of things (like those listed just below). Engines like the M60B40 were designed to last for over 800,000kms, so just because an 8-Series has high mileage doesn't mean it should be discounted from your list. As long as things have been replaced since then and servicing has been done at least every 10000 kilometres thereafter to keep the engine and other things in good shape.
Regardless of kilometres, other things on a car this age that should be cared for are things like the cooling system (ie: radiator, water pump, thermostat and hoses), the suspension and steering (eg: shocks, upper and lower control arms, bushes, etc.), braking system (brake booster, brake pressure accumulator, etc...), and fuel system (Fuel Pump, Filter, etc.). Make sure some - if not all - of these things have been replaced, otherwise you'll have to foot the bill eventually! Some of these things deteriorate with age, and not just kilometres!
Value For Money:
Because the V12 versions are heavier and more costly to work on, the V8 versions are more sought after - especially by people who have done their research and realise that there is only a small difference in power, yet much more difference in weight (and handling) between the two.
All said and done, the V8 versions are just great to drive - whether just cruising around the city, or on the open highway. They also get plenty of looks from EVERYBODY, partly due to the fact that they look nothing like other BMW's, and also due to the fact that all 4 windows go down (the car has no 'B' Pillar), and it is only one of two BMW's ever made that has pop-up headlights.