Low oil pressure after boat was not started for two years
 

Two motors, when the boat was last ran the oil pressure was 70 psi. both motors. Just changed the oil and started the boat and now the starboard pressure is 20 psi at start up idle. If I rev it up it go's up to 80 psi. So I put it in the water to test and oil pressure went to 0 psi after about 5 minutes, bumped the throttle and it and it went back up to 20 psi. Took the boat out of the water and put a mechanical gauge on the oil cooler block to check the electric gauge and pressure was the same 20 psi. The motor is not tapping or knocking, sounds fine. Then I thought the oil pump pick up fell off the pump so I added several quarts of oil to bring the level up with no change in pressure.

What could cause this?

What engines, exactly?

And...you just "added several quarts of oil" to an engine? Seriously?

Mercury 502 with 250 blowers
https://cimg3.ibsrv.net/gimg/www.off...8978ef776e.jpg
The reason you add oil is to get the level up past the oil intake on the pump and pressure would be good if the pick up fell off, then drain the excess oil, just at test.

I have seen oil pump relief valves stick open after sitting a long time. I think they get surface rust in the bores and then as soon as they open they stick that way. The fact that it goes up to 80 when you increase the rpms would somewhat verify this too.

That is a very easy and very common diagnostic procedure to see if a pickup has possibly come loose. Nothing wrong with it at all.

Are you talking about the pressure regulator on the pump or the pressure relief valve in the block or oil filter block?

Pump

The one in the oil pump. The one in the block really has nothing to do with oil pressure.

One thing that I would do before running the engine any more is to take the filter off and cut it open and check for metal. Just in case something else is failing and causing the problem.

Yep, could even be a bad oil filter even. I usually cut open all of my oil filters to check engine health; which reminds me...
...I did NOT cut the oil filter open on my race car when I changed it last month. I need to do that.

If the oil filter is good with no metal in it and regulator spring is stuck open. Does anyone have any idea on how to fix without dropping the pan?