Why the BMW S85 V10 doesn't deserve its bad reputation

Over the years BMW's M division have developed some truly spectacular engines. The E46 M3's raspy S54 straight-six pushed the boundaries of specific output for a naturally-aspirated unit, as did the S70/2 V12 used in the legendary McLaren F1 back in the 90's. The Bavarian marque aren't just famous for their sixes and twelves though; motors such as the S62 V8 used in the E39 M5 have developed a cult following, not to mention the mighty S65 used in the E90-series M3. However, there is one M engine from BMW's hallowed naturally-aspirated days that seems to be the source of significant angst. But the question is why?

As the only V10 engine ever developed by BMW, aside from those they produced for F1 cars, the S85 is probably the most unique engine you'll find inside any BMW model. Displacing 5.0 litres (4,999 cc), this motorsport-inspired engine ran a 12.0:1 compression ratio with a bore of 92 mm (3.62 in) and stroke of 75.2 mm (2.96 in). Built entierly from aluminium alloy, the S85 used ten electronically actuated individual throttle bodies, a quasi-dry sump lubricating system with two sumps and twin scavenge pumps, and an ionic current measuring system for knock sensing. Producing 507 BHP or 373kW/520Nm, it redlines at 8,250 rpm and sounds absolutely sensational.

Picture: BMW

Picture: BMW

What are the reasons then that the S85's reputation has been tainted? There are a variety of explanations for this, but primarily they revolve around a lack of undestanding (or fear of the unknown), confusion about specific issues or paranoia as a result of spending too much time in internet forums. Like all European high-performance engines the S85 does have the propensity to need more care than your standard A to B commuter car, however this applies to every BMW M engine. So what makes the V10 any different? In short, nothing at all. The main issue you will hear repeatedly uttered by paranoid individuals about the S85 is "rod bearings". The internet will have you believe that the connecting-rod bearings in every single BMW V10 will be chewed up and kill the engine if you don't replace them. Why this type of scaremongering has been directed specifically towards the S85 I am unsure, because the truth is it is not specific to this engine at all.

Almost every M-developed engine from BMW since the ninety's until now have been known to run very tight tolerances between the crankshaft journals and rod bearings, typically resulting in premature wear on the bearings. It was such an issue on the S54 that BMW even recalled the E46 M3 due to the problem. S62's were not immune from the issue either, however the E39 M5 did not see significant enough failure rates for BMW to deem a recall necessary. The more modern S63 twin-turbo V8 which remains in production to this day has been known to see this failure occur as well, not to mention their raft of other problems such as stretched timing chains, failed valve-stem seals or faulty fuel injectors. Perhaps the worst engine of all for bearing issues is the S65 V8, which not only can experiance premature rod bearing wear, but wear on the main bearings too. While replacing rod bearings can be done without removing the engine and typically costs between $2,000 to $3,000, main bearing replacment requires engine removal and complete disassembly, which as you can imagine could easily end up costing a large portion of the cars entire worth.

Other than the S54 which prompted a recall, the truth is that failure rates on these engines are overblown by the internet and in many cases can be attributed to factors such as incorrect warm up routine, abusive driving practices and failure to properly maintain or service the car at the correct intervals. As has been said many times, people will post about their bad experiences online but you rarely hear about the good. Based on the information above, it is quite puzzling why rod bearing fears seem to get directed at the V10 more than any other engine. While yes, there have been documented failures even at quite low mileage, there are also many cars that have made it to 200,000+ miles on their original bearings.

Picture: BMW

Picture: BMW

Now that we have the 'big one' out of the way, let's discuss some of the other issues that may occur on the S85. One of the most common problems are the throttle actuators which are used to electronically open and close those ten individual throttle bodies (five per actuator). For unknown reasons, BMW decided to cheap out on the gears inside the actuators which are made from plastic instead of metal. This issue was also very common on the S65 V8 due to its design being partially derived from the S85. Thankfully, it is pretty straightforward and even cheap to solve depending on your approach. Some opt to disassemble the actuators and replace said plastic gears with metal ones, while others prefer to buy completley new units. There are even a few companies out there who specialise in the repair and will exchange faulty units for repaired ones at a relatively small cost. For the most part this issue won't even put the car out of action, it will simply enter limp mode and operate with low power.

Earlier S85's built prior to January 2007 did have a few more issues than later units which received a range of revisions. These included the VANOS oil pump and oil line, and the solenoids and VANOS actuator units themselves which operated the variable valve timing system. In addition to this, engines manufactured after this point had two oil drain plugs (one for each sump) oposed to just one for the main sump on early vehicles. For this reason, if you are considering buying a car with the S85 that was built prior to this date, either make sure that previous owners have taken care of these items or budget on doing it at some point in your ownership. If you do have an early engine and are reading this don't be too scared, as failure of these components is not guaranteed and many engines are still healthy at even higher mileages, but it just pays to be aware. One common error made by those who speak ill of the S85 is tarring all of the engines with the same brush. Later units are significantly more well sorted than early ones and remove many of the expensive repairs that may become necessary from the equation altogether.

Picture: BMW

Picture: BMW

Despite not actually being part of the engine itself, one of the things that seems to frighten potential buyers away from the S85 is its 7-speed SMG III (Sequential Manual Gearbox) transmission. Automated-manual gearboxes such as these were very popular in the day and appeared in many cars from Alfa Romeo's to Ferrari's and Lamborghini's. In fact, the Lamborghini Aventador still uses one. So what about them makes them unattractive to S85 buyers? There is a common misconception that these gearboxes are prone to issues and have a shortened clutch life. While this is often the case with exotics that used such transmissions, based on reports in forums the SMG seems well and truly capable of getting well over 100,000 kilometers or 60,000 miles out of a clutch depending on how the car is driven. One thing you'll often hear mentioned, more so on the older SMG's in the E46 and E36 M3's is 'pump failure'. This refers to the hydraulic pump which is reponsible for providing the pressure needed to actuate gear changes and clutch movments. The pumps themselves rarely fail, but what can cause issues is the electronic motor inside them. Rather than replacing the entire pump which can be very costly, the motor can be replaced individually saving thousands. SMG components also got a refresh on newer cars so typically problems are more common on 2005 and 2006 models, although repair costs are no higher. It's also worth mentioning that the SMG III mated to the S85 is significantly more refined than previous iterations found in older M3's and shifts far quicker, not to mention the fact it is a lot more reliable.

Picture: Wikimedia Commons

Picture: Wikimedia Commons

So there you have it. The BMW S85 V10 is not the scary, horrendously unreliable, bank account destroying monster that the internet wants you to believe it is. In fact, it's actually more reliable and has less potential catastrophic faults than some of the other M engines out there (we're looking at you, S63). M car ownership should be a joyous experiance, not one dominated by fear and paranoia, so if you've got one of these wonderful cars, get out there and enjoy it. Be precautious for sure, but don't let scaremongering ruin your ownership experiance.

If you're in the market for an S85 powered M car, hopefully this article has opened your eyes to the fact that this engine should not be avoided for any reason, but is instead something special that should be celebrated. Do your due diligence when buying, make sure the car has been well looked after, and there's no reason that S85 ownership should be any less enjoyable and rewarding than the other M engines out there.