I've already outlined why it's critical to repair an oil filter housing leak on any BMW N5X engine (N51, N52, N52N, N54, or N55). I've even highlighted how to fix the issue yourself in a DIY article. Now, I have the photos to back up how bad this can be. And I should should warn you—it's not pretty.
Oil leaks are a nuisance, but are usually harmless. I haven't seen too many higher mileage BMWs that don't have some kind of oil leak that goes without repair. The truth is, most are difficult to fix and less caring owners simply don't want to invest the money into completing the repair.
If there's one oil leak on the N5X series of engines that is critical to address, it's the oil filter housing gasket. This rubber gasket seals the oil filter housing to the cylinder head and is one of the most common source of oil leaks on most BMW engines where the oil filter housing bolts to the engine block or cylinder head.
Now, why is oil filter housing gasket leak this serious of an issue on the N5X family of engines? Put simply, it can lead to engine failure. Yes, you read that correctly, and no, I'm not exaggerating; it can in fact lead to engine failure and I have photographic evidence from an N54 engine that met its demise. Again, I want to reiterate that this is from what started as an oil filter housing leak.
What you're looking at are shards of serpentine belt material that are inside of the engine. How does serpentine belt material end up inside an engine? It's due primarily to the design of the harmonic balancer/crank pulley assembly on the N5X engines and the position of the serpentine belt relative to the engine block. The oil filter housing leak, when severe enough, can create a trail of oil all the way down the front of the timing cover, eventually coating the serpentine belt and crankshaft pulley. Once oil is on the serpentine belt and the crank pulley portion of the harmonic balancer, it's almost inevitable that the serpentine belt will slip off. Since the harmonic balancer is in front of the crank pulley, the serpentine belt has nowhere to go but back towards the timing cover if it slips off. Once it slips off the crank pulley, it shreds the belt and forces the pieces through the front crank seal.
Unfortunately, the N54 in the photos above suffered this failure. It appears that a new front crank seal was installed and the oil leak was repaired. However, whoever made the repair didn't bother to inspect as to whether the serpentine belt was sucked inside the engine (they probably thought it was flung off). This engine had severe rod knock, and once it was opened up it became pretty clear what went wrong. The amount of debris in the oil pick-up tube likely created an oil starvation issue which eventually led to rod bearing failure. There, more likely than not, is other damage in this engine based on the amount of debris found inside of it.
The takeaway here is that it's important not to overlook an oil filter housing leak on these BMW engines. If there's a small leak I'm not telling you to pull over and get the vehicle towed; what I'm saying is what starts off as a small leak almost always gets worse. In the case of N5X engines, a severe oil filter housing leak that can be repaired with a relatively inexpensive gasket can end up costing you thousands of dollars later on or worse, a complete engine replacement.
