I think a few poeple with high performance boat engines, like
supercharged tall deck big blocks, have similar high clearances and run
50 or 60 wt racing oil. Then people think if it's good for a racing
engine then it should be good for me. Not considering that they have a
completely different engine.

Gene Kearns wrote:
On 5 Jun 2006 20:03:26 -0700, wrote:

. Straight weight oils (even as thick as SAE 50) do not have the
?film strength? of multi-viscosity oils such as 5W-20, 5W-30, and
10W-30

This is opposite of what research I have done says and what I have
personally seen in aviation engines. Film strength of multi-viscosity
oils fails when the viscosity improvers fail under extreme pressure.
The oil molecules will re-link in the sump as they cool off, but the
damage to the metallic parts is done.

I would NEVER recommend multi-viscosity oils in extreme pressure
situations (barring really cold starts) and the valve train is a great
place to find such situations. I suspect the article's advice is
driven by people using way to thick an oil.... SAE 50 in an aircraft
engine is the standard... but then it has HUGE clearances compared to
a water cooled boat engine.