because 30w does not lube pressure oil bearings as quickly upon engine
startup
as does 5w-40. Not by a long shot. you can hear the difference, easily.

My point is Merc says to use 10w-30 OR 25W-40. (the only grades they sell)
30HD seems to be right in the middle.
Merc doesn't make 30HD and I suspect that has more to do with the recomendation
than anything.
I do know their 10W-30 is breaking down after 20 hours and I am losing oil
pressure. That is not a good thing.

Before you ask, no they don't have any answers ... I asked.