i get this too on 1 engine
. Contribute to air bubble play.
However, I get even more interesting one: Saildrive oil
alternates between minimum level which is recommended and slightly above maximum.
After I check cold, and level is close to min level (optimal), go out, come back and before going out next time check again. Level is slightly above max. Oil clean. First time suspected water
Then go out come back and again check before going out next time and level is again near min ( optimal) and clear.
And this alternates up and down...