How does all of this translate to outboards that run 120f thermostats?
If the oil is formulated for 210 degree operating temps (most cars) does it
still work at 120-150?
I notice my merc 4 stroke has pretty low oil pressure 20-30 hours into an oil
change when I run Merc 10-30. If I use an auto brand it acts the same way. It
does better with merc 25-40

10w-30 at 150* will give less oil pressure than 30W at 150*

The advantage of multi oil is engine lube at ambient temp start up.