Heres a good article i found about the 850i part-1
It facinates me the opinions people dribble about the BMW 8 Series being a "mechnical nightmare" or "expensive to maintain", and "prone to failure". All from individuals that have never owned one themselves. Let's quit guessing about the car and come up with some facts:
The 8 Series, like any mechnical device will have failures over time. All things entropy. It's the way things are in the world. That said, this car is incredibly reliable. My current '91 has 135K miles on the 5.0L 12 cylinder engine with zero engine work done. Both of my '92's were sold with over 100K miles on them with also no engine work done. The good and bad thing about the E31 is they have a list of consistent items that DO fail. The good thing is that these are KNOWN items that most owners, dealers, and competent service technicians are aware of. They are:
Driver's side seat will twist due to a cable bunching up. This is a do-it-yourself fix.
The power motors do eventually go bad in the power seats depending on the use.
Since this is a 12 cylinder, there are two air filters, two ECUs (computers) and two DK Motors that control the drive by wire. These are basically servos that feed the fuel to the bank of cylinders. These are known to fail after 70K miles. I have yet to ever replace these on any of my cars.
The On Board Computer (OBD) is a display made up of orange pixels. Over time some of the pixels will fade or not show. This is also a simple fix. This is a common problem on ALL BMWs, even the brand new ones. My wife drives a 2001 525i and it's been in the shop more than all of my 8 Series cars combined. It currently has 2 pixels out now.. very small. More annoying than anything.
Wear and tear items are typical of ANY car with high mileage and for an older vehicle: Control arm bushings, brakes, tires, suspension bits. The 8 Series is a heavy car. After 95K miles, the suspension will start to show it's age, and the steering will not be as tight as new. Nothing unusual here.
Some 8 Series owners have had the maniford leak and causes a rough idle. It is very noticable when this happens. The car is normally so smooth, that is is within US Specifications to balance a quarter on the engine block.
There is dual-climate control. Over time the heater control valve which opens and closes the heat vents in the floor and in the defrost vents will fail causing the air to be warm even with the A/C on. The part is $140.00 and is a DIY replacement, or about 3 hours labor with a service shop.
That's it for known problems. Of course, depending on how well the car was maintained by the previous owner, there could be other issues. The above listed items are for a documented, well maintained 8 Series. As you can see, nothing that warrants the car be labeled as "Mechanical Nightmare" Remember that is was quite overwhelming for a car in 1991 and even up until the late '90s to have dual climate control, a steering wheel that has power tilt and telescope, 3 position memory seating that also sets the side mirrors, headrest, and steering position. The steering wheel moves up and out of the way and back down again when the door is opened. The windows will partially go down when you pulled on the inside or outside door handle to create a better seal for very high speed driving aerodynamics and an extremly quite cabin. The car has a built in cell phone with voice recognition. The windows automatically go up over 90mph if they are down to seal the cabin and improve the aerodynamics.
Really, though, these "complex systems" are nothing less than standard features now on most newer BMWs and even most mid-grade passenger cars. Will they too be labeled as "complex systems prone to failure" when they get older? My wife's 2001 525i has all of the above features as standard equipment (except the windows dropping, which is now a standard feature on all BMW convertables). Her car was rated as the best car ever tested by Consumer Reports. Edmunds also rates the car very highly. Yet, it has the same complicated systems that the 8 Series has. In fact it has more! The car is rated well and deemed reliable but has been to the shop much more than any of the 8 Series I have owned.
Maintainence?? Well, I owned a '91 BMW 535i before my first 850i and paid $49.00 for an oil change service as the BMW dealership. I now pay $69.00 for the same service on my 850i. The only additional cost with the 12 cylinder is that there are two oil filters and two air filters. The 5.0L. 5.4L and 5.6L (in the Csi) have basically two in-line 6 cylinder engines in them. In fact the car is so reliable that if you WERE to have an engine failure, the car will automatically shut down the side of the engine with the problem and go into "limp home mode" and continue to run safely on 6 cylinders!
Brake fluid, steering fluid, coolant, brakes, etc. are all the same price as any other BMW. If someone tells you differently, then it's a myth, or they are a service shop that is trying to rip you off. BMW has what they call Inspection I and Inspection II Service. This is basically all-inclusive tune-ups, oil change fluid flushes, etc. The cost difference between my wife's 2001 525i (it has over 45K miles so it's not paid for by the dealer anymore after 36K miles) and my '91 850i for the Inpection I service is $57.00. For the Inspection II service the 850i costs $75 more.
Speaking of service shops, all BMW dealers are aware of this car. The V8 engine in the 840i is the same engine in the 540i and 740i which were produces en-masse. The 5 liter engine in the 850 is the same as the 750i. There is no "mystery" to these cars. The first question you must always ask when taking ANY car to an independent shop is: "Have you worked on this make/model car before" If the answer is no, then don't be the guinea pig! If yes, make sure you are up on the basic knowledge of the car and test your mechanic to see that they at least know for instance, that an 850i comes with a 12 cylinder engine.
Regarding the 8 Series being a marketing failure or a failure at anything, this too is a myth. When the car was introduced at the German auto show in 1990, BMW took so many orders in that one show, that they filled the production of for 3 years. If you were to place an order for a 1991 BMW 850i in 1991, you would get your car by the end of 1993. Thus, they never spent money on advertising the car. Think about it. How many BMW 8 Series TV ads do you remember? How many 8 Series print ads did you read? The 8 Series sold on it's own. Total Worldwide sales were 30,621 units for an "exclusive car". Some failure.