1989 520H Floppy Oil Drain Pipe

[Kissinger_520H 3]

So I posted this question in another thread and got a few suggested methods of fixing it, but no one actually answered my question of how the oil drain can flop around so loosely but somehow not leak oil? Can anyone illuminate this curiosity of mine? 

[Ed Kennell 41,880]

That is a tapered pipe thread that relies on the threads to make the seal.   There is no gasket or "O" ring.       The alternating low pressure to vacumm created by the piston movement in the crankcase  does not push the oil thru the loose fitting tapered pipe thread.   

[Handy Don 14,035]

25 minutes ago, Ed Kennell said:

That is a tapered pipe thread that relies on the threads to make the seal.   There is no gasket or "O" ring.       The alternating low pressure to vacumm created by the piston movement in the crankcase  does not push the oil thru the loose fitting tapered pipe thread.   

Yep. There is adequate “tightness” in the threaded joint that the oil is constrained.

One of the oil companies used to advertise oil poured into a cylinder comprised of a simple stack of metal rings where the oil didn’t leak out.

[squonk 43,759]

But yet a fairly tight pipe plug will seep oil

[Handy Don 14,035]

16 hours ago, squonk said:

But yet a fairly tight pipe plug will seep oil

A problem that has plagued the pundits for decades....

[Wild Bill 633 877]

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