Excellent explanation Dan. Pressure and volume are related and in just the
way you have described. I have heard much wrong information and thinking
about this over the years. You are also right about the hot viscosity being
the one that matters (except when the engine is cold of course). And I
agree that a synthetic of the proper viscosity should be fine. This,
however, does not address the issue of cost. Is the synthetic worth the
money?
A few years ago Consumer Reports magazine did a comparison test on different
brands of motor oils. They had a bunch of identically rebuild engines and
then ran them for something like 60,000 miles each in New York City taxi
cabs. The engines were then dissembled and inspected. I don't recall that
there was much difference between the various brands of oil. I don't recall
if synthetic oils were involved in the test. It is difficult to get past
peoples personal opinions about synthetic oil. Has anyone seen a reputable
comparison test?
-----Original Message-----
From: owner-buick-rover-v8@autox.team.net
[mailto:owner-buick-rover-v8@autox.team.net] On Behalf Of Jones, Daniel C
Sent: Wednesday, February 16, 2000 12:13 PM
To: buick-rover-v8@autox.team.net
Subject: RE: Motor oil
> David Hardcastle discusses oil viscosities for the Rover V8 engine in at
> least one of his two Rover V8 books ("The Rover V8 Engine" and "Tuning the
> Rover V8"), and he describes the oiling system in this engine as a
> "volume"
> system rather than a "pressure" system.
>
I don't really see any difference. Pressure and volume are related.
The oil pump sweeps out a volume of oil. The restriction (to flow)
that the pump sees determines the pressure. Thicker oil, tighter
clearances, and smaller passages will increase pressure. Increasing
the volume swept out by the pump (per unit time) by either increasing
the rpm or the depth of the pump gears will increase pressure up until
the bypass limit is reached.
The difference between high volume and high pressure oil pumps
is that high volume pumps use long gears to increase the volume
(and hence pressure) at all rpms up until the limit is hit. High
pressure pumps simply have higher bypass pressures so the volume
and pressure stay the same until the original limit is hit, then the
volume and pressure go up (with rpm) until the new bypass limit is
hit.
> Providing the oil in sufficient volume tends to require sufficient (read
> higher) oil viscosity
>
The viscosity that matters is the hot viscosity. A 5W50 *should*
perform as well as a 15W50, both having the same hot viscosity
as a straight 50W oil. The actual performance does vary from
manufacturer to manufacturer.
I can't see any reason a synthetic of the proper viscosity shouldn't
work fine. BTW, the Buick 215/Rover V8 oiling system layout is
identical to a Buick V6's, except for galley lengths and diameters.
Dan Jones
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