My Mercruiser owners manual specifically does not recommend synthetic oil.
"The use of non-detergent oils, multi-viscosity oils (other than Quicksilver
25W-40), synthetic oils, low quality oils, or oils that contain solid
additives are specifically not recommended."


"Jim Kelly" wrote in message
...
I think you are getting your balls in a bunch. You are confusing extreme
pressure properties of certain types of lubricants with the ability of
both
synthetic and conventional oils to operate satisfactorily in the typical
boundary layer lubrication environment of an internal combustion engine.
You
need to read up on tribology and the mechanics of an oil film in plain
bearing
applications as well as sliding motion applications. The most detrimental
aspect of lubrication in an internal combustion engine is contamination
from the
combustion process. Unlike a gear box application, the oil in an engine
is
subject to the byproducts of the combustion process as well as unburnt
fuel.
For this reason, changing the oil and filter on a regular basis is much
more
important than the type of oil used.



"Frank Taylor, Jr." wrote:

Well, I'm not sure what that quart of "Volvo Duraplus Synthetic Oil" is
that
is sitting right in front of me as I write this message is but it sure
looks
like synthetic oil to me. I suppose that it could be manufactured by
some
other company and Volvo just puts their name on it.

You are correct, that the temperature characteristics of synthetic oil
are a
big advantage of synthetics but it goes much further than that. The
molecular structure of synthetic oil is also much more consistent than
that
of conventional oil. Consider this analogy:

Lets say you have a bunch of steel balls of all different sizes and you
thrown them down on a concrete floor and then throw a board on top of
them
and step on it. As you surf across the steel balls on top of the board,
you
are really only ridinng on the large balls. The surfaces on these few
balls
will soon wear down and the ride becomes rough. This is how
conventional
oils works.

Now you do the same thing with another bunch of balls that are all the
same
exact size. Since they are all the same size, the board rides evenly
across
all of the balls at the same time. Since all of the balls are
supporting
the board, they do not wear down nearly as quickly and the ride starts
smoother and stays smoother for much loinger. That is what synthetic
oil
does.

Yes, synthetic oil is more expensive but it's cheaper than a new
eingine.

Frank

"Jim Kelly" wrote in message
...
Volvo does not make any oil, synthetic or conventional. Statements
like
"synthetic is definitely much better" are meaningless. Synthetic
lubricants
have properties which make them a better choice for certain
applications.
If
the application does not take advantage of these properties, there is
nothing
to be gained by using them. One of their greatest attributes is a
more
linear temperature vs. viscosity curve. There is a misconception that
synthetics are simply higher quality. This is not the case.

"Frank Taylor, Jr." wrote:

30 wt refers to the viscosity charactersitics of the oil. It can
still
be
either conventional or synthetic. As a matter of fact, Volvo makes
a
straight 30 wt synthetic oil for its marine engines.

"WaIIy" wrote in message
...
On 16 Dec 2003 17:09:51 -0800, (Bear) wrote:

(Bear) revised earlier message
.com...

'97 Chapparal w/ a Volvo-Penta 5.7L Carb w/ SX Outdrive

Questions:

1) Volvo pushes synthetics for crankcase and outdrive, yet all
the
boat places around me (Austin - San Antonio) said to use
regular
20w-50 motor oil in crankcase and non-suynthetic in
outdrive...
Of course they said to change every 100 hours or per season.
Experience / Opinions?

2) Any thoughts / experience on spark plugs for this motor???

Thanks!

Hmmm, the people I talk to in Ohio say to use straight 30 wt in
my
1989
5.7.