I agree seen it a few times.
You may not have gotten all the oil out of the one engine.

swap sending units

did you have impeller go at all? maybe clogging water side of oil cooler? restricting it under way then cools at idle.... just another thing to look at...

Do you have oil temp gauges?

Also, water pressure gauges? that will tell you if you have a restriction...

Its not the oil side of your cooler, your motor would have to be self destructing for that to have anything in it. Prob sending unit, have seen more sending unit problems on these than anything, swap sending units

Something to keep in mind. Electric gauges rely on voltage input , sending unit resistance, and ground connection. Twin engine boats, can have multiple batteries, long runs of cable to battery switches, long runs of wire from engine to helm, back to engine again , various splices, etc.

Electric gauges are only as accurate as the signals provided to them. Before i go chasing a ghost, i would put a mechanical on it, and verify if you even have an issue with oil pressure in the first place . Swapping sending units may not do anything if the issue is a voltage issue at the dash, engine, battery, etc.

exactly! the easiest to verify is mech gauge...

I hate electrical gauges.

This weekend I am going to install mechanical gauges at the motors and see what story they tell. I can make a run and take a look. Thx for the tips.