Having owned, disassembled, and cared for a 2007-2010 BMW 3 Series I’m familiar with what really kills these things. The weak spots of the N54 engine are becoming brutally clear at the age and mileage these cars are now achieving, but there are some issues in particular that need immediate attention if you’re driving one. A $15 gasket could cost you this powerful three-liter twin-turbo straight-six altogether.

A critical failure in this car can be caused by a cascade of catastrophes stemming from one very simple but problematic part: the oil filter housing gasket.

Images: Chris Rosales – Left Image: Sealing surface where the oil filter housing gasket leaks out of. Right image: Overview.

Pictured above is the oil filter housing and oil cooler assembly we need to talk about. It’s an aluminum assembly fastened with three E-Torx bolts on the engine cylinder head. The mating surface between the oil filter housing and the head has a rubber gasket that gets hammered with heat, oil, and coolant circulating within the housing. Over time it gets hard as a rock, and will allow oil to leak down the front and side of the engine. Crucially, it also leaks onto the serpentine belt and pulleys. 

The pulleys on the N54 engine seem to be designed a little strangely. Out of the eight total pulleys, half do not have V-ribs. Instead, they are smooth. Two of them are in series, next to each other. In the photo, those are the top two pulleys to the left side. They are directly under the oil filter housing, and receive the brunt of a potential leak. Because the two smooth pulleys are right after one another, the belt seems nearly guaranteed to walk and move on the pulleys, hit the front timing cover, and slowly shred itself to pieces.

Images: Chris Rosales – A closer look.

Once the belt starts to come apart its metal bands get exposed, torn, and can end up whipping around the engine bay. This is where a truly bizarre and disastrous issue can come up: The belt can cut the engine’s front main oil seal. While that’s happening, pieces of torn-up belt get fired into the timing chain and oil pan, potentially causing three catastrophic results: 

  1. Metal belt material gets lodged in the timing chain, causing timing to skip or fail; valves hit pistons; engine becomes inoperable.
  2. Rubber accumulates in the oil pickup, clogging it, now oil can flow into the bearings and other crucial engine parts; engine becomes inoperable.
  3. The oil leak from the front main seal starves the engine of oil. Once it’s empty, you guessed it, the engine becomes inoperable.

The moral of this little story is pretty straightforward: If you’re looking at buying or maintaining a 2007-2010 BMW 335i, 135i or 535i, make sure to inspect the oil filter housing gasket. Beware of the little piece of rubber that can betray the N54 engine.