As with most modern BMW engines, the valve cover and its rubber gasket are known to develop oil leaks with age. The gasket starts leaking first, but lifting the brittle, plastic valve cover to replace it could easily cause it to crack - and then leak even more! For this reason, we recommend replacing both the valve cover and its gasket at the same time. The rubber oil pan gasket is also prone to start leaking with age. This problem is not as common as valve cover gasket leaks, but it involves a lot of work to replace it because the procedure entails removing the front subframe to gain access.
Oil-filter housing and gasket leaks are a known issue with BMW N54/N55/S55 engines and are once again caused by the use of plastic for the oil filter housing. Like the valve cover, the oil filter housing also uses rubber seals, so the oil leaks will eventually surface in this area. If the filter housing gasket leaks internally, it could result in oil and coolant mixing, reducing the oil's lubrication properties and contaminating the engine's bearings in the process - eventually leading to internal engine damage. Leakage to the outside also has the potential for causing harm, because the leaking oil will degrade the serpentine drive belt, which could then disintegrate and lead to more-severe engine damage. Fortunately, these components are mounted in front of the engine, so the repair won't cost too much on labor charges.
Many important components in a BMW M2 or M2 Competition engine are sealed plastic units, which can only withstand a finite number of heat cycles before degrading, and their thermostat housings fall squarely in this category. Both the N55 and S55 engines can be prone to thermostat housing failure, and this problem must be addressed before it leads to overheating and a potentially-fatal engine failure. This is quite a labor-intensive repair, so best schedule it to be performed while the oil filter housing is being replaced at around 60,000 miles.
Another common BMW issue, which is likely to start around 70,000 miles, involves the Vanos control solenoid failure, usually due to perished rubber seals. This isn't a difficult item to repair, and BMW can supply either a complete solenoid assembly or a solenoid valve repair kit to remedy this problem.
Mileage: Gasket leakage manifest around 50,000 miles and the valve cover can crack from 100,000 miles. Expect oil pan leaks from around 100,000 miles. Oil filter housing gaskets often start leaking from 50,000 miles, while the filter housing itself could start leaking from 80,000 miles. Thermostat housings usually fail from 60,000 miles, but some owners reported failure as low as 36,000 miles. Vanos solenoids fail every 70,000 miles or so.
Cost: An OEM valve cover gasket costs about $40, a valve cover about $580, and labor will be close to $1,000. Roughly $44 for an oil-pan gasket and up to $1,000 for labor. About $300 for an OEM oil filter housing, around $29 for the gasket, and about $200 in labor. About $115-$140 for an S55 OEM thermostat assembly, $500 for labor if performed as a single repair. About $400 including labor to replace a Vanos solenoid or $200 for an OEM solenoid valve repair kit.
How to spot: Valve-cover leaks result in a smell of burning oil, smoke coming from a hot engine, and visible traces of oil leaks on the cylinder head. Oil-pan leaks lead to drops under the engine and frequent oil top-ups. Oil-filter housing leaks cause visible oil leaks in front of the engine, oil spots on the serpentine belt, oil drops under the engine, and a frequent need for top-up oil. Failed thermostat housings lead to visible signs of coolant leaks in front of the engine, a need for frequent coolant top-ups, and overheating in the worst cases. Vanos failure causes inconsistent performance, hard starting, rough idle, and an illuminated Check Engine Light.