A frustrating problem that has even plagued seasoned BMW technicians. You replace a valve cover gasket for a leak and the vehicle will come back still leaking. Even worse, not the only engine that has this issue. In this post I will focus on the most common engines the N62, N54, N52, N20.
N54 is the one we see the most in terms of having an oil leak from the plastic cover cracking. The best way to tell if your cover is leaking is to look for oil stains in the valley by the injectors and ignition coils. The cover cracks, typically right below the crankcase vent cyclones.
Above, you can see there is a hair line crack in the cover causing this leak. Normally, no fault codes or drivability concerns are found when this occurs. The crack is hard to see, so best way to find any crack is a smoke machine. I understand the average person doesn’t have access to a smoke machine. A good inspection for the oil traces are the next best thing.
The N20, though not as common as the N54, still have a lot of them. Normally, plastic cover cracks in the back rear corner of the cover towards the exhaust manifold. This one is a hair line crack that is extremely hard to find, smoke is still the best option. Watching oil trails is another way to find a leak, but can be difficult and small to follow.
The N52 cover is a different leak most of the time. They can still crack, but most of the time what leaks is the oil separator control valve. Normal signs of this can be oil staining around the valve and in the last two ignition coil valleys. It is normal to find oil leaking from the valvetronic motor seal and eccentric shaft seal. At times, right below the valvetronic motor there will be a large pool of oil from a leaking seal. Those are not a valve cover crack issues, just the aged seals.
The N62 normally doesn’t crack on its own. I find most of the time when the cover is cracked its because someone installed the cover wrong. Don’t get me wrong, those N62 covers are a pain to install and can be easily damaged. The common repair of upper timing cover gasket is usually when we see a return car with oil leaking from the cylinder head cover. This is because it was installed incorrectly and cracked. Normally, you will find the crack towards the bottom of the valve cover close to the exhaust. The cover has 3 guides on them and if not seated correctly against the cylinder head; when you tighten down the cover it will damage and cause the leaks.
Hopefully this points out some common issues, saving you from replacing a gasket and still having an oil leak.