On Sat, 09 Oct 2004 17:38:16 -0400, Gene Kearns
wrote:

On Sat, 09 Oct 2004 20:14:39 GMT, Short Wave Sportfishing
wrote:

On Sat, 09 Oct 2004 20:06:26 GMT, "DanO" wrote:


"Short Wave Sportfishing" wrote in message
...

we recommend the use of Mercury Precision 4-Cycle 25W-40
Marine Engine Oil. This oil is a special blend of 25-weight and
40-weight oils for marine .

What crap! If you blend 25 and 40 weight oil you don't get 25w-40 you get
an average viscosity of the two oils based on their ratio. MM's 25w40 is
formulated the same way everyone else's mulit-weights are. They start with
a base 25 and add polymers (assuming that it's dino oil).


They probably start with a viscosity near 25, but the point is that
25W is a relative number used to rate the "crankability" of an engine
at low temperatures. A base stock, somewhere between SAE40 and SAE25
is employed and pour point depressants are added to make the oil shear
at lower temperatures.... thus the engine spins easier.

At 100 Deg C 5W-40, 15W-40, and SAE 40 should be in the same kinematic
viscosity range. At cold temperatures.... the lower the W number the
easier the engine will crank... single weight will (obviously) fare
the worst.

Note that the amusing point is that this specification doesn't address
pumpability.... as one poster here steadfastly believes. For
pumpability, one should reference the Borderline Pumping
Temperature... which gives the minimum temperature at which you may
expect adequate flow through your engine.

You know - in between the other BS, you glean nuggets of wonderful
information.

Neat info.

Later,

Tom
-----------
"Angling may be said to be so
like the mathematics that it
can never be fully learnt..."

Izaak Walton "The Compleat Angler", 1653