Originally Posted by Stretch

The oil filter housing in the OM617 is a complicated beast it does a little bit more than just hold the filter in place.

There's a full description of the intended functionality in chapter 18-005 in the FSM.

A certain amount of oil should be held within the oil filter housing after the system has been operational - oil should be held in place by a non return / check valve at the input to the housing. The minimum level is depicted by the blue line in the picture below.



In practice I assume that this level might be higher due to capillary action / close proximity of the filter sides to the housing and a residual amount of oil contained within the filter.

In a simple "geometric" situation when a filter is not fitted; pouring oil directly into the filter housing:- some of the oil should pool in the bottom of the filter housing and not drain away into the engine. If this doesn't happen then I would suspect that the non return valve in the filter housing (shown at the big black arrow just above the number 4) is leaking. This would not be ideal as the whole filter housing could drain when the pump stops pumping - resulting in oil starvation at start up, as the pump has to pump the oil for longer to refill the housing before it gets to the parts other beers can not reach etc...

...the red arrows show the direction of the flow out of the filter housing after it has passed through either the fine or coarse part of the filter elements.

I hope this information helps.