I'd start by changing the oil and filter one more time and ensuring
that you use straight HD 30 weight oil. Those are hard working
engines and multi viscosity oils like 10W-30 can be a problem.

I would tend to disagree about multi viscosity oils being an issue -
unless you use a very wide range oil (10W30 is nominally very stable)
or the oil is an exremely off brand or very used.

However, in this situation, I would also recommend a straight weight,
high quality oil, unless you are using this vessel in a wide range of
ambient temperatures (winter use, etc).

This is not probably not related to your problem, however, with one
caveat. If the oil was whipped up into a foam, then again you would be
introducing air into your oil system, causing the oil pressure to drop.


Again assuming that you are not running a dry sump system and that the
lower end has not been touched, overfilling the oil pan can cause the
oil level to get into the crankshaft, causing the oil to be sheared and
whipped into a foam. The lack of a required windage system can also
cause this issue.

Most wet sump engines that are used for marine and high performance use
have a windage tray in the crankcase that prevents oil from being
whipped (when the oil level is at the correct setting). Since you did
not state that any lower end work was performed, we will assume that
any windage system should still be in place.

Thanks -
GPG