BMW S85 M5, M6 Reliability & Common Problems
The BMW S85 is an absolutely gorgeous 5.0L V10 engine. With 500hp and an 8,250 redline the S85 engine sounds insane. Even as an older engine, its 100hp per liter is among the best for NA engines. It’s hard to hate a naturally aspired engine making 500hp and revving to 8,250. However, the S85 suffers a few common problems that may lead to expensive repair bills.
BMW S85 Common Problems
- Rod bearings
- Throttle actuators
- SMG Transmission
- Valve cover gasket oil leak
To note – this certainly is not an exhaustive list, especially with the age of S85’s now. Any wear and tear items are fair game on 10+ year old cars with potentially 100,000+ miles. Valve cover gaskets and oil pan gaskets are among a few gaskets that may cause leaks on many BMW’s north of 10 years old. Anyways, in this post we’re going to focus on a few of the bigger issues with the S85. Rod bearings, throttle actuators, and SMG transmission problems could potentially cost thousands of dollars each.
We don’t intend to be overly harsh to the S85 M5 or M6, however they’re definitely cars for a select few. With their age and mileage they probably make the most sense as second cars. With the cost of parts and repairs you may also want to be a skilled DIY’er or have a bit of money on the side. Again, the S85 is truly a gorgeous engine. However, the M5 and M6 were nearly $100,000 cars when new and they demand the maintenance and repairs you’d expect out of a high-revving V10.
1. BMW S85 Rod Bearing Issues
Worn rod bearings are one of the hottest topics for the S85 engine. This issue is shared alongside the M3 S65 V8 of the same era. The two engines actually share the same rod bearings and it’s not hard to find information on rod bearing failures. Forums may have you believe the issues are way more common than they really are. However, S85 rod bearing failures do warrant concern.
These bearings are responsible for holding the connecting rods on the crankshaft. If they wear down and are left alone for too long it may lead to complete engine failure. As they wear down they may score the crankshaft. Additionally, too much bearing play may cause rod knock and eventually lead to bent rods. Not good.
However, even if you catch the issue in time it’s still not cheap. The rod bearings can be replaced without pulling the engine. Although, it’s still a very labor intensive job. Estimates from repair shops may be all over the place, but expect $2,000+ in labor alone. The Genuine BMW bearings are about $800 for all 20. However, we would advise opting for aftermarket “upgraded” rod bearings. Depending on the degree of wear there may be other labor to remove any metal shavings. Additionally, you may consider replacing the oil pump tensioner, front and rear main seals, and VANOS high pressure line.
S85 Worn Rod Bearing Symptoms
- Ticking sound at idle and lower RPM’s
- Metal shavings in oil
- Engine failure
There really aren’t many warning signs or symptoms in the early stages of S85 bearing failure. You may notice a faint ticking sound, however it’s not always noticeable. Metal shavings that look gold/copper indicate potential wear of the bearings. Of course, rod knock or engine failure are not the symptoms you want to come across. There are other problems that may cause engine failure, but rod bearings may be the cause. Due to the lack of symptoms, some opt to upgrade or replace their bearings as preventative maintenance.
*It’s recommended to send your oil to BlackStone Labs (or a similar company) for oil analysis. That will often help pinpoint if there are small metal shavings in the oil.
S85 Rod Bearing Replacement
As we briefly touched on above – rod bearing replacement isn’t cheap. Some owners choose to do this as preventative maintenance every 60,000-80,000 miles. Most rod bearing issues seem to pop up in the 60,000-100,000 mile ballpark. It’s possible only a few bearings are worn, but it’s recommended to replace all of them while you’re in there.
This DIY should be left to the experienced willing to spend a weekend in the garage. If you’re going to a repair shop expect to spend at least $2,000 in labor and an additional $800+ for parts. Depending on the degree of wear there may be other work and repairs required. Again, S85 rod bearings may not be as frequent of an issue as some may indicate. However, it’s talked about often for good reason. Rod bearings are not cheap.
Replacement Cost: ~$1,000 in parts and $2,000+ in labor
2. S85 Throttle Actuator Issues
This is another common problem shared with the S65 V8 engine found in the M3. The S85 uses 10 throttle bodies controlled on two banks. Each bank has a throttle actuator to control the throttle bodies on that bank. It’s often the gears inside the actuators that actually wear down and fail over time. As such, there are repair kits that offer new gears to fix the issue. However, the actuators occasionally fail electrically. It’s suspected the worn gears cause constant adjustments and eventually overheats the electrics.
This post may be a helpful resource for anyone experiencing electrical issues with the throttle actuators. It seems some S65/S85 owners have found ways to repair the electrical issues without needing new throttle actuators. Although, it may take someone knowledgeable and experienced to successfully go this route.
S85 Throttle Actuator Symptoms
- Limp mode
- Fault Codes CDC0, 2B21, and/or 2B57
There typically aren’t any warning signs for throttle actuators, but rather they fail quite suddenly. Once the failure occurs you’ll generally be thrown into limp mode immediately and the engine may run a bit rough. Fault codes CDC0, 2B21, and 2B57 will also commonly appear indicating a potential throttle actuator problem.
S85 Throttle Actuator Replacement
There are a few different routes you can go to replace the S85 throttle actuators. You can opt to purchase the throttle actuator repair kit found here. This repair kit comes with all 4 gears to replace the gears within the two actuators. If you’re actuators failed in a different way, such as electronically then the repair kit will not work by itself. In that case, you may need to opt for two new throttle actuators. They cost about $650 each and it’s generally advised to replace both at the same time.
Labor is likely in the ballpark of 2-3 hours for an experienced mechanic and up to 4-5 hours for less experienced DIY’ers. It takes a little time but it’s not an overly complicated repair. Given the time to repair, expect most repair shops to charge about $250-400 in labor.
Replacement Cost: $100 for repair kit OR ~$1,300 for two new actuators, $250-400 labor
3. S85 SMG Transmission Problems
Many recommend looking for a manual transmission S85 M5 or M6 for this very reason. However, MT examples are hard to come by. We typically keep these guides to engine problems only, but the M5 SMG is not cheap to repair. The major issue lies within the hydraulic pump motor on the SMG automatic transmission. It’s not a cheap part coming it at ~$800 for a Genuine BMW pump motor. There are also several other problems that may pop up with the SMG transmission, though the pump is the most common.
It’s a great transmission when it’s running right. However, it’s not uncommon for SMG issues to pop up in the 60,000-80,000 mile ballpark. Sticking with the overall trend with the S85 it’s an expensive repair.
S85 SMG Problem Symptoms
- Slow/hesitant shifting
- Fault codes
- Trans malfunction light
The pump is responsible for building up pressure. When it’s failing and pressure is inadequate you may experience very slow and hesitant shifts. Fault codes and a transmission malfunction light will also point you towards the SMG transmission. It’s possible for other components to fail, such as the clutch sensor or pressure accumulator. However, the pump motor is generally the most problematic and first to let go.
S85 SMG Pump Motor Replacement
Again, the top part linked it the most likely to fail. All of the parts are fairly expensive, though. Additionally, expect at least a few hours of labor for all of the above repairs on the SMG transmission. All in all, you’re probably looking at $1,000+ total and potentially more if there are several problems within the SMG unit.
Replacement Cost: $600+ in parts, $500+ labor
4. S85 Valve Cover Gasket Oil Leaks
We’ll make this one rather quick because it might not be completely fair to call it a common S85 problem. More so, we want to highlight the fact that the S85 engines are getting old. With age and mileage, rubber gaskets are subjected to constant heating and cooling cycles. Eventually these gaskets degrade and begin cracking. The valve cover gasket is an excellent example. Many BMW’s experience some sort of gasket oil leak in their lifetime, and the valve cover is usually towards the top of the list.
Again, it doesn’t seem too many S85 owners have experienced this issue yet. However, it could simply not come up in conversations because people are more concerned with the several thousand dollar repairs above. There are two valve covers and valve cover gaskets on the S85 M5 and M6. They’re basic gaskets and only cost about $25 each. However, labor can be anywhere from 4-6 hours so repair costs can add up at shops.
We’ll leave the valve cover gaskets at that. The important take-away is that you should expect miscellaneous issues to pop up on the S85. It may be coolant hoses, gaskets, water pumps, etc. It’s simply part of owning an older high performance, high revving V10 engine.
BMW S85 Common Problems Summary
As we stated earlier the S85 really is an awesome engine. It’s truly one of the last of its kind. Naturally aspirated, high-revving V10 engines are a thing of the past as manufacturers look towards smaller, efficient turbo engines. However, the S85 suffers a few common problems that aren’t cheap repairs. The most notable and likely the most widely discussed of S85 common problems lies within the internals. Rod bearings are a scary issue since they could potentially lead to complete engine failure. Even if you catch the rod bearings early it’s still a $3,000+ job at a shop.
The S85 also suffers common problems with the throttle actuators and SMG transmission. Both problems that can potentially add up to $1,500+ repair bills. Finally, as an aging engine any wear and tear parts are fair game for failure. Many BMW’s suffer gasket oil leaks, faulty water pumps, cracked coolant hoses, etc at 10+ years and higher mileage. All of these repairs can add up if you’re taking your M5/M6 to the shop. They can also be frustrating repairs even for intermediate and experienced DIY’ers.
The S85 isn’t a bad engine. However, it’s definitely not for everyone. We believe the S85 M5 and M6 are best suited to those willing to invest the time and/or money and who appreciate the engine as one of the last of its kind. It’s probably not the best fit for moderate enthusiasts concerned with the potential for several thousand dollar repair bills.