1994 mercury EFI 225

by pete
(south shore long island)

engine running fine but then son ran 2 stroke oil low and 4 beep alarm started. he added oil once back at dock and it appeared to be resolved (he did run boat with 4 beeps to get back to dock). the next trip out after approx 30 minutes the 4 beep alarm returned and then a steady alarm , like an overheat, temp guage reads steady at 160 same as it always has. the steady alarm only comes on after approx 1500 rpms, the motor runs rough but as soon as rpm is lowered engine smooths out and steady alarm goes off but not the 4 beep alarm which is now on as long as engine running.
new impeller and poppit valve last year, change impeller every other season. all totally fine until low oil alarm. 21ft proline, runs on south shore of long island ny. he did run boat on outside with slight seas getting lightly bounced around a week prior without issue but oil was obviously low because that next trip is when 4 beep alarm started. both tanks have oil now main and on engine. hearing may be sensor in tank, may need to bleed or burp air out etc.... also how to make sure oil pump is working from 2nd tank into motor and would this cause the steady alarm at 1500 and like it goes into protection mode, if it has such a thing. the steady alarm was on the way back in on 2nd trip not sure if oil sensor could trip steady alarm or just coincidence with other issue like bad temp sensor. thank you.