Since I filled my 1991, 750iL with Mobil 1, 0W-40, the low oil level
alarm has started going off when the (overnight) dipstick level is 1/4
of the way down from the high mark.

I have heard that synthetic oil "clings to the surfaces", and thus
takes longer time draining to the oil pan compared to conventional oil,
and this seems like a confirmation of that. It probably takes 6 hours
to get a repeatable oil level reading, prior to that, the level slowly
increases.

Has anybody else seen this, and if it is true that synthetic oil drains
down slower, would the optimal oil level be higher than for
conventional oil, or would the risk of overpressure exist during
startup?

Jan Fure