On my 850 NA 1995 I removed the oil pan to see how things were doing inside (at the same time as I took off the cylinder head for some valve work). All seems ok for the age of car. I am ready to replace the various seals and reinstall the pan, but I am unsure about the 10 mm hex fitting that is screwed into the pan from the inside, near where the oil filter goes. It looks like it should be a pressure relief valve that would let some oil flow back into the sump from the inlet side of the oil filter (the periphery of the filter, not the center).

This little fitting is open - I can blow some air through it either way. It seems to me like it should be closed, unless the pressure is really high. It doesn't appear to have a spring or ball or anything like that inside it - it's pretty small.

Can anyone tell me if this is really a pressure relief valve or something else, and how it's supposed to behave? Is it just an orifice of fixed size?

thanks
ksg