"JAXAshby" wrote in message
...
My Mercruiser manual says to use 5-40.

What the hell is that? so 10-40 isn't good enough? Real reason is to
cause F.U.D. to discourage boat owners from doing work themselves.

no, 5w-40 lubes better upon ambient temp engine startup that 10w-40 and
much
better than 30w or 40w does.

however, the difference between 5w-40 and 10w-40 isn't all that great. In
past, 5w-40 didn't hold up as well under long service, and so was seldom
sold.

Thanks all. With all that, I don't see any reason that a 20w-40 or 20w-50
would not be a preferable choice to plain old SAE 20, 30, or 40 which are
all recommended in my 1987 manual.
-Dan O.
Minneapolis