Max,
The way it was explained to me is modern cars are built to very tight
tolerances. A very thin oil pressurizes the oil system just fine,
and a metered amount flows though into each place oil is supposed to
be. And the theory is, an old car, built with looser tolerances, and
perhaps showing some wear, needs a thicker oil to do the same
thing. It's like pumping water into a vertical perforated pipe
(sealed, except for the perforations). With big perforations, all
the water will come out of the bottom few holes. Small perforations
will allow water to flow out of all of the holes. Replace the water
with molasses and the large holes will all see some flow. Try that
with the small holes and very little molasses will come out, though
the pressure inside will be high. Therefore, different engines need
different viscosity oils.
-Steve Trovato
strovato at optonline.net
At 01:36 PM 6/22/2011, Max Heim wrote:
>There is also a lot of misunderstanding regarding how viscosity relates to
>oil pressure, and what that actually means. People assume they need a
>"heavy" oil to maintain oil pressure. A higher viscosity oil is harder to
>pump and may therefore give a higher pressure reading on the gauge, but it
>also restricts the rate of oil flow, which may lead to oil starvation at the
>bearings. What the bearings require is a continuous oil film -- this is a
>function of flow rate, not pressure. The reason we talk about oil pressure
>is because this is a property that is easily measured with a gauge -- it
>isn't a good in and of itself. The measurement of oil pressure is merely a
>crude substitute for the oil flow rate measured at the bearings, which is
>unobtainable, from a practical standpoint.
>
>--
>
>Max Heim
>'66 MGB GHN3L76149
>If you're near Mountain View, CA,
>it's the primer red one with chrome wires
|