An interesting one here....and one that may not be spotted easily.
The car in question is an E39 525i with an M54 engine - but this should apply to any M54 engine'd car.
There is approx 240,000 miles on my car at the moment as a guide.
For some time the oil filter housing to block interface has been weeping - a common issue with these and one that can often be blamed on the sump gasket. It is due to the rubber gasket going hard after many cycles due to plasticizer migration due to heat.
Last week I pulled it in for a closer look - it was indeed weeping. I also pulled off the oil filter cap to check if I had the correct filter for a service and noticed that the bowl was dry. Considering it was just 5min after shut down this sent off alarm bells in my head. The bowl should not be empty that soon after shut down, or at all. The bowl is to remain filled for a long period after shutdown - as in days, not minutes. The reason for this is when you start the engine - the bowl/filter housing is already filled with oil ready to be pumped to head and hydraulic buckets and not delayed while the oil fills all housings/drillings. I did notice the top end a little noisy after a hot start but put it down to the hydro bucket age.
In nearly all engines including my F1 engine - a non return valve exists somewhere to prevent oil from leaving the filter bowl/head area on shutdown.
On 95% of passenger cars the non return valve to head lives in the oil filter housing. With that in mind I ordered a complete new housing from Bmw. This includes the alloy housing, the cap, new seal to block, and a Bmw oil filter(A nice surprise!). At approx 400euro it was a bit of a gamble but one I was willing to take.
Removal is pretty easy and about a 20min job. It involves two oil pressure/temp sensors, the belt tensioner, and a banjo fitting up-to the dual vanos that have to be swapped/refitted.
Below shows the footprint of old one that had been weeping for a while as can be seen,
The new complete part from Bmw below - I thought it was good value @400euro odd as its pretty large and includes the seal, filter, crush washers for sensors/banjo and bolts, and luckily....the non return valve which I'll come back to,
On closer inspection of the oil housing, something can indeed be seen amiss with the non return valve, its lugs are broken off and is sitting crooked within the tapered counter-bore,
Compared to the new unit,
Since there is no drilling at the rear of the housing to install the plastic non return valve, I figured it must be a separate piece, and pressed in from the front as there is no way to install it or machine the seat otherwise. Sure enough it was and with a bit of prying out it came,
Seeing daylight out between the plastic piece and the seat told all - its pretty easy to see now too that once the lugs break off it can no longer sit square in the hole or seat correctly,
In cutaway form its very apparent, notice the centering guide lugs gone, (where!!?)
Compared to the new ones,
There is also evidence of fretting on the perimeter of the valve as can be seen below - it should never touch off the alloy counterbore in this area if it was seating square,
With the complete housing on it looks the biz,
It is always a good idea to fill the new one half way with oil into the outer chamber - as you can see....the non return valve is now preventing the oil from draining back down,
I've since found that the non return valve is available from Bmw as a separate item. However, with the oil glaze and general years of living inside the housing its pretty hard to remove without marking the housing faces.
So that's that. At that mileage I guess the non return valve breaking down is to be expected, but its a shame its not an alloy or steel part since its pretty critical for keeping the top end oiled right after startup via anti leak down tactics. But it is what it is.
Its a very easy check in-case you are concerned about your M54 engine - minutes after shut down remove the oil filter housing cap and filter. If there is no oil in the outer chamber your return valve is dead and should be investigated.