2008 SN 206 - oil pressure warning after heavy use

I changed my oil recently and used the wrong oil (5w-30) and began getting a low oil pressure warning after running and bringing it down to idle - I immediately changed the oil and used PCM's recommended 15w-40 and all is well.

However, this past week-end I ran it at WOT for less than a minute or so and when I brought it back down to idle when pulling into the dock I got the low oil pressure warning again (down at 5psi or below) but when revving up a bit would go away as pressure increased.

Next day ran a few sets at 3,000 or so RPM's (speedo not working per earlier post) and when pulling into the dock I got the warning again.

This boat has the EX 343 motor, has 900 hours on it and runs very strong - starts up imediatly every time, runs well, no blue smoke, etc.

Looking for some advise here - hoping that my rings aren't warn - has been well taken care of - prev owner did all oil changes and maintenance regularily .. etc.

Could my OP sensor be wrong? Only way to test with a manual OP gauge?

Thanks for any advise ...

If the gauge and warning was fine before I wouldn't go suspecting that. I might drain the pan and fill back with straight 40 for a few hours (or longer if its happy) then back to 15-40.

You probably know this, but when changing the remote filter you need to make sure the old gasket comes off, most likely if it did not you would see some oil leaking at the bottom of the filter.

Don't do nuthin but add another quart of oil, same stuff that's in there. Go back to running, report back what you find. If its right the extra quart shouldn't hurt it in the short term.

My van had the same issue with low pressure at idle but otherwise fine. Switching to high mileage oil, (which has more zinc) raised the pressure back up. Been fine ever since. Maybe the 5 30 had more detergents in it...