1999 mercruiser oil pressure drops bad after 3000 rpm

[jabfd]

Hi All,
i have a 1999 mercruiser 4.3 serial #OL319690

i ran the boat first time this season and realized that my riser were bad and that my oil pressure was going down after 3000 rpm. between 5 and 10 psi.

so far i replaced manifolds and risers also changed the oil because the level was elevated i didn't get a milk shake but i definitely thing there was water in the oil. i know have a slight knock at idle that goes away when i bring the rpm above idle. i am still getting low oil pressure after 3000rpm ? at idle i have over 40psi and bringing the rpm up i climb to almost 55 psi however after 3000 rpm it just drops down.

any help will greatly appreciated
thank you

 

[alldodge]

have a slight knock at idle

This isn't good, if its an actual knock as in rod bearing

What weight oil are you using?
Connect a mechanical gauge to see if its actually loosing pressure and not a gauge or sender issue

 

[jabfd]

Hi All

I installed a mechanical oil pressure gauge and over 3000rpm i have 65psi.
sender unit was bad i replaced it and it now confirms what the mechanical gauge was saying.
i still have a light lifter noise only at idle. i did take the boat yesterday for a 2.5 hours cruiser and she ran fine. thank you