if ANYone tells you multi grade oil "thicken up" after they warm (I saw the
clown from Mack Boring, Larry Berlin make that very claim in a seminar), invite
them to put a $100 bill on the table. Then, you pour room temp 10w-40 oil into
an old frying pan on the stove. notice how it moves around when you tilt the
pan. Turn on the burner and wait a couple minutes. Then tilt the pan again
and notice how the oil moves around.

Duh. any clown who tells you multi's "thicken up" has not once in his life
pulled a dipstick on an engine with multi when at room temp and again when at
operating temp.

dumb, dumb, dumb.

I don't want to get in the "less filling" "tastes great" battle about whether
multi grade oils thicken or stay the same over the 0 - 210f range but I do
know
that 10-30 starts out holding about 40 PSI right after a change in my boat
and
in about 15-20 hours it is more like 35. Something is going on.
That is using Merc oil or a good auto oil. If I bump it up to 25-40 it is
better. Straight 30 acts about the same as the 25-40.
Since I am never going to be in my boat if it is much below 70 degrees (air).
I
am not sure why I am not just running 30HD. Cooling water will range from 67f
to 88f (5 year min/max) based on the water samples I do for the state.