[audi20v] Re: Low oil pressure 200 20V

Bernie Benz b.benz at charter.net
Mon May 5 09:52:38 EDT 2003

> From: "Paul Caouette" <paxnobis at angelfire.com>
> Bernie,
> I'm curious. I have much the same thought on oil flow. The more the better
> regrdless of oil pressure. However low oil pressure at high RPM is s sign of
> easy flow. This usually means that a path of least resistance exists somewhere
> in the system.
The total in parallel combined paths to the sump, bearings, cyl wall spray
jets, et al, is the restriction upon which the measured pressure is built.
> I beieve that there is only one path where restriction that is
> dependant on wear and that is on the bearing surfaces of either the cams or
> the con or main bearings. Is that how you see it?
Correct!  Further, the supply oil pressure has absolutely no effect upon the
operation of a friction bearing (mains, rods, wrist pins, cams).  They are
self feeding, requiring only a full flooded supply of oil at the enterance
to the load bearing wedge of oil.  Within this wedge pressures are
developed, supporting the bearing load, that are orders of magnitude greater
than the supply pressure.  The frictional heat is generated by shear within
the wedge oil film supporting the load.  The bearing is cooled both by the
excess oil flowing out the sides of the bearing and that which is trapped
within and travels thru the wedge.
> My second question relates to the by-pass valve.
> Isn't true that if the by-pass valve opens at a certain pressure the flow to
> the rest of the gallery is reduced by the amount of flow that goes through the
> valve? In other words it's a bleed-off valve that is pressure sensitive.
Yes, it is a shunt relief valve.
> and..
> With an older engine the valve rarely actuates except at high RPM since the
> pressure relief point is never realized at modest RPM.
> Or do I have it all backwards?
Right on, Paul!

> --
> On Mon, 05 May 2003 06:43:21
> Bernie Benz wrote:
>> Opps!  Sent this to the wrong 20V list.  Sorry guys.  But you may comment.
>> Bernie
>> Scott,
>> There was no reason for nerviousness IMO, and your rebuilder did right by
>> you!  A new, tight engine needs more oil cooling (more flow volume) for the
>> wear-in period than does an old dog.  Any oil flowing thru the pump's
>> pressure relief valve due to excessive pressure is not available to the lube
>> system for oil cooling, filters not withstanding.  Old dogs can at least
>> tollerate high viscosity oils, even if not needed for lube.  As stated in
>> conclusion several days ago, "Low oil pressure is good, no oil pressure is
>> bad."  Why apparently is the list hung up on an illigical desire for high
>> oil pressure?  Nonsensical IMO.
>> Bernie

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