You need to cut open the filter and see what is inside. If there is a bunch of metal then you know what it is. There are little bypass valves in the block & the thermostat they could be defective.

I have seen Fram filter problems. Use the merc filter. One other thing you may want to check. I had 5 CMI Headers fail last year. Leaking water into engine. Only signs of problem was low oil pressure and oil temp would shoot right up. Usually after 5-7 minutes 230F ... 10 Minutes guage pinned. Merc Racing took the long block back and found corrosion clogging oil thermostat in cooler. I also would not recommend synthetic oil in that motor. I had a 525 wear a cam lobe last year and merc deined the claim due to synthetic oil allowing the roller to slide on the lobe instead of roll.
Just my .02 ...

I checked the oil when I was having the problem and it did not have any water in it and was at a normal level. oil temp never went above 240. If there was a problem with the cooler I would still think that oil pressure would stay up. I just can't see what would make the pressure drop from 80# to 20# with new oil, cool temps on a 32 hour motor. If a oil pump would go out, it would be 0

I've heard stories of oil pressure dropping and alarm sounding when, after running hard, the throttles are brought back to quickly...

first off you should be using a wix or a merc filter,seond the 15-40 is a little light for your mtr should be running a straight 40 or 25-40

Maybe a dumb answer and question here. But Isnt the oil pressure gauge right in the oil galley in the block? So if the oil pump was making pressure or not, the oil pressure is picked up and registered before the oil filter and adapter. So I would think that changing the filter to try it again would be a waste of time other than to check the filter and see what is inside. Also remember, if there is something wrong the more times you start it to check stuff out, the more damage you might be doing.

I have also had a few engines do some weird stuff with the grounds loose on the bellhousing grounding studs. May not be that for you but is a place to check and see if nothing is found with the oil and filter.

Good luck with that.
Let us know what you have, I'll keep my fingers crossed for you.

John S.

Just a update. I spoke with Bob at mercury racing this morning about my low oil pressure and high oil temp after changing oil. He said that he was sure it is the oil filter. He said that when the oil filter is clogged or restricted it will kick open a by pass valve that returns oil to the engine and by passes the oil cooler. That is why the oil temp is up and the drop of pressure. I picked the boat up from the boat shop today and changed filter. I did not see any thing unusual about the filter I took off. I will take to lake and test hopefully in the next few days.

You have to cut the filter open

do you know of a easy way to do that?

well I cut the filter apart. I did not see anything wrong with it.