The S85 5.0-litre V10 engine is an incredible piece of engineering, but you need to go in with your eyes and wallet open. A rattle on start-up is not a precursor to the end of the world, or your financial well-being, it can be as simple as letting you know the motor needs an oil top-up. It can also be a warning of impending timing chain wear or stretch though. Its service schedule is dictated by the variable indicator, but you can reckon on a full service every 9,000 miles or so. Use an official dealer and an oil change alone, using Castrol Edge 10w-60 oil as recommended by BMW, will cost £336. Add in the micro filter and the price goes up to £432, while spark plugs at every third halt top that up to £890.
On the plus side, the V10 is not prone to problems with the VANOS variable valve timing. Still, it's worth looking at the condition of the sump-to-cylinder head hose and the VANOS pump. The throttle actuators are another area that needs checking, as a failed item is £600 to replace.
In a worst case scenario, big end bearings can spin and wreck the engine. This is not common to all engines though it is something you need to be aware of, as it will result in a bill of more than £10,000 for a replacement. There's not much you can do to spot it before it happens, as the engine warning light is usually the only heads-up you'll get just before the motor lunches itself. The preventative care necessary to avoid this means paying for new bearings, likely to cost around £650 plus fitting. You'll also have to budget for a reground crankshaft as part of the job, but it will future-proof the motor.
When it comes to economy, 17mpg in town is typical and up to 28mpg for motorway driving is possible. The trip computer won't read less than 7mpg, but track driving can see the consumption dip below this mark. It's best to run the engine on premium fuel and most owners recommend Shell V-Power. With a 70-litre tank, you can get into an expensive habit if you use all of the power all of the time. A Fast Attack Motorsport remap for engine and gearbox improves response and power, and there are other remaps out there that claim up to 600hp can be freed up with no other alterations.
Clutches are a common sore point with M5 and M6 owners, with the 'Red Cog' warning on thedash a source of many sleepless nights. This is partly down to the SMG being an automated manual, meaning town driving can see the system ride the clutch and burn it out quickly. Early cars also suffered from the SMG pump failing, earning the car a poor reputation on this front. However an upgraded SMG pump was fitted from 2006-on, curing this problem and coming with updated software to aid stop-start driving. A failing SMG pump is often spotted by slow shifts and a warning symbol appearing on the dash display. Check any car for how smoothly it picks up from a standing start and how it reverses.
Oh BMW, why didn't we get the manual too?
Another clutch-related issue to watch for is a worn release bearing and guide bush. The guide bush needs to be correctly lubricated when replaced, or it can lead to a judder as drive is taken up. When they fail, it can often be mistaken for a worn clutch and, as a result of this problem, a lot of owners have ended up paying to replace entire clutch assemblies, rather than just the bearing and bush. It's also partly why the M5 and M6 are noted for wearing out clutches in as little as 30,000 miles, when some owners report 90,000-mile intervals before needing this work. A full clutch and parts replacement can cost £2,500 at a dealer, so it can be a huge saving if only the bush and guide need swapping. A new clutch from Euro Car Parts costs £800 plus fitting.
The rear limited-slip differential has to cope with a lot of power, and also with some quite sudden gear changes if the previous owner never learned to use the SMG 'box smoothly. However it's tough, and a distant whirring noise from the diff is normal when making tight turns at parking speeds. Listen out for any whining or thunks though, with the latter pointing to worn mounting bushes.
Some owners will have fitted an aftermarket exhaust. How much you like this is down to personal taste, but look for good brand names such as AC Schnitzer, Eisenmann, Supersprint and Tubi to ensure good quality.
PHer's view:
"Launch control is fun but absolutely useless! It just spins and fish-tails the backend. DSC off with gearbox in manual and using good throttle control gives you the best launches."
Daniel Lewis
