If you're interested in purchasing an S55 powered M2, M3, or M4 reliability is an important aspect to consider. As M cars, they're certainly not cheap up-front. In this article, we will cover a few common problems with the BMW S55 engine. However, please keep in mind - this is in no way an exhaustive list of all potential issues. All cars and engines will have issues at some point.
BMW S55 Common Problems
- Crank Hub
- Valve Cover & Valve Cover Gasket Leaks
- Oil Pan Gasket Leaks
- Oil Filter Housing Gasket Leaks
We'll provide additional insight and analysis on these S55 problems below. However, we should note - this post may be a bit premature and some of these common S55 problems are speculation. For example, the S55 oil filter housing and gasket are the exact same parts as used on the N54 and N55. It's well known they are common issues on those engines. However, the issues typically don't pop up until 80,000+ miles. Quite frankly, there aren't enough S55 engines with this kind of mileage so it may not be a common issue yet. Though, it's likely safe to assume if the same design is faulty on older engines then these problems will likely become common on the S55 as it ages.
1. BMW S55 Crank Hub Issues
Let's get this out of the way first. We hate calling this a common problem for several reasons. For one, it's really not a common problem. This issue has been completely blown out of proportion. However, there are enough discussions regarding faulty S55 crank hubs that it's worth diving into a bit deeper. We do agree - it's a shame the S55 didn't receive a keyed crank hub from the factory. Regardless, the S55 shares the same crank hub components as the N55 engine (many of those parts are also shared with the N54). Guess what? Yes, the N54 and N55 can experience spun crank hubs. However, the problems are very isolated and uncommon.
Now, the S55 makes 600+whp a lot easier than the N54 and N55. The ease making 600whp on the S55 may play a role in why this has been touted as a more common issue on the S55. Nonetheless, we wouldn't hold our breath even at those power levels. Understand spun crank hubs can be an issue on the S55. However, don't expect the problem to happen (unless you're simply one prone to terrible luck). Even on higher horsepower, modded cars, spun crank hubs seem to occur on less than 1% of S55 powered M2, M3, and M4's.
Additionally, it's not a problem that warrants too much concern to the point preventive upgrades are necessary. Generally, when the crank hub spins it will throw off engine timing. You'll simply need to correct the timing and replace the crank hub. In extremely rare cases, a spun crank hub may cause additional internal engine problems. Again, that's extremely rare and will likely only occur if you continue driving and beating on the S55 with an already spun crank hub.
S55 Spun Crank Hub Symptoms
- Drivetrain malfunction light
- Limp mode
- Rough idle/stuttering
- Engine fault codes
There are no pre-mature symptoms of crank hub failure. It's not something that occurs over time, but rather the S55 crank hub slips out of the blue. Once it occurs you will typically see the drivetrain malfunction light and limp mode. Additionally, you'll notice a rough idle and stuttering due to the timing being thrown off.
2. BMW S55 Valve Cover & Valve Cover Gasket Oil Leaks
As with the N54 and N55 - and most other modern BMW engines - the S55 valve cover (VC) and gasket (VCG) are prone to cracking and leaking oil. The rubber valve cover gasket is prone to degrading with age and mileage. Rubber gaskets subjected to high temperatures and constant heating/cooling cycles generally do not hold up well. Eventually, the rubber gasket cracks which results in oil leaks. The S55 valve cover gasket is the exact same part as found on the N55.
The plastic valve covers themselves are known to crack, as well. It's certainly less likely than the gasket leaking oil. However, we highly recommend replacing the valve cover along with the gasket. That may be overkill early on, but as S55 engines begin nearing 100,000 miles it may be a good idea to replace the valve cover if the gasket is leaking anyways.
There have already been plenty of cases of leaking valve cover gaskets on the S55. It's not unheard of for the valve cover to begin leaking before 60,000 miles. Two of our N54's developed valve cover gasket leaks as early as ~7 years old and ~75,000 miles. However, these oil leaks are most common around 80,000-100,000+ miles. We suspect in the coming years we'll hear of more and more valve cover area leaks.
S55 Symptoms of Leaking Valve Cover Gasket
- Low engine oil light
- Burning oil smells
- Smoke coming from valve cover area (generally passenger side)
- Oil on spark plug threads
If you're topping off oil unusually often it could possibly be caused by an S55 leaking valve cover gasket. Look for signs of oil leaks on the passenger side of the engine just below the engine cover. The leaks are often on the passenger side due to the tilt of the S55. Burning oil smells, especially with the A/C or heat on, may be a dead giveaway of an oil leak. Also, with a warm engine you may see smoke coming from the valve cover area. Finally, oil leaking into the spark plug tubes and onto the spark plug threads may indicate a valve cover or valve cover gasket leak.
Should You Replace a Leaking S55 Cover or Gasket?
This subject could be up for debate. It's not an absolutely urgent repair. Driving with a leaking valve cover or gasket is unlikely to cause any additional harm. Ultimately, we still recommending fixing the issue. However, how soon to fix the leak may depend upon how bad it actually is. It's possible the oil is leaking onto engine mounts, belts, and extremely hot turbo components. Hot oil surely won't help the lifespan of engine mounts or belts. Additionally, oil dropping onto hot components could pose a risk of fire. If it's a minor leak you can probably get away without replacement for a little while. However, it's going to need repair at some point so best to knock it out sooner than later.
3. BMW S55 Oil Pan Gasket Leaks
Once again, the S55 has another gasket that is shared with the N55 engine. Similar to the previous gasket leaks we mentioned, the S55 oil pan gasket is prone to degrading and cracking over time. On other BMW engines these gaskets often hold up to 100,000+ miles. It's not quite as common of a leak when compared to valve cover gaskets and oil filter housing gaskets.
However, the oil pan gasket replacement requires dropping the sub-frame. Dropping the sub-frame is not a quick job so the labor on this repair can add up. The gasket itself can be found for around $25 and it's a pretty easy repair once the S55's sub-frame is dropped. As such, we recommend replacing the oil pan gasket anytime the subframe is dropped. We recently had a lot of suspension work done on our 2007 335i which required the sub-frame to be dropped. We replaced the oil pan gasket as preventative maintenance. It definitely can't hurt to do and potentially save another 5+ hours of your time (or another $1,000 repair shop bill for a $25 gasket).
S55 Leaking Oil Pan Gasket Symptoms
- Low oil
- Oil leaking onto ground
Sometimes oil pan gasket leaks are tough to detect, especially given the possibility of different oil leaks. Low engine oil could be caused by many things, however it potentially indicates an oil pan gasket leak. Given the oil pan gaskets location at the bottom of the engine you'll typically notice oil leaking onto the ground (or onto the under-body shield). Again, other leaks could cause oil to drip onto the ground or panel.
4. BMW S55 Oil Filter Housing Gasket Leaks
This is probably getting old to read. Anyways - yet again - the S55 oil filter housing (OFH) and gasket (OFHG) are the same parts found on the N54 and N55 engines. Over time, the gasket becomes brittle and cracks leading to oil leaks. One of the biggest concerns with a leaking oil filter housing is that the oil often drips onto the belt. An oil leak dripping onto the belt is never a good thing. It could cause the belt to snap or slip off the pulley, which could potentially cause damage to other engine parts. Additionally, if the S55 OFHG leaks for a long period of time or leaks severely there is a possibility of oil and coolant mixing.
In addition to the gasket, it's not unheard of for the actual S55 oil filter housing to develop leaks. Though, the gasket is definitely most likely to give out first. These issues can pop up as early as 50,000 miles. However, most oil filter housing leaks develop in the 80,000-100,000+ mile ballpark. The gasket itself is very cheap and a fairly simple DIY. We prefer the idea of replacing the entire oil filter housing, especially if you're north of 100,000 miles. That's the approach we took on our N54 when we replaced it preventatively at 110,000 miles.
S55 Leaking Oil Filter Housing Gasket Symptoms
- Oil leak from oil filter housing area
- Oil on belt
- Low oil
The key here is simply inspecting the OFH and belt area every so often to check for signs of oil leaks. Again, be cautious of oil leaks that are dripping onto the belt. If left too long you may consider replacing the belt & pulleys, as well.
BMW S55 Reliability
Overall, BMW's S55 engine is truly an excellent performance engine solid reliability. Many of the issues we've discussed throughout the post aren't necessarily "common problems" as of yet. However, the three oil leaks - valve cover gasket, oil pan gasket, and oil filter housing gasket - are all common parts with the N54 and/or N55. It's fair to speculate the S55 will too share those common problems. However, many of the oil leaks develop after 5-7 years and 80,000+ miles. There simply aren't enough S55's with that mileage to say how common these issues will be. Nonetheless, if you're in the market for a long-term S55 keep these problems in the back of your mind. It's possible you'll run into at least one or two of these oil leaks before 100,000 miles.
Fortunately, all of the above oil leaks are cheap gaskets. For the DIY crowd they are relatively easy repairs. However, they're time consuming so you should either be willing to spend a day or weekend in the garage or dish out a decent chunk of money for labor. Nonetheless, the BMW S55 engine is off to an excellent start reliability wise. Time will tell if and when any other common problems pop up on the S55 platform. However, right now the S55 looks like one heck of an engine that can make 600+whp with basic bolt-ons and do so with respectable reliability.
What's your experience been with the S55? Feel free to drop a comment and let us know.
Or check out our post about how to build a 600+whp S55