The oil pressure is a function of how tight the various bearings and
wear surfaces are in the engine, combined with the inherent friction of
the various surfaces of the engine, the viscosity of the oil, the sizes
of the orifices the oil passes through in relationship to the oil pump
output. Oil is incompressible, and because of such relationships, it
becomes very important  that the fits and clearances be maintained with
in the specified limits. The pump works against a pressure head created
by all the above, and to prevent an over pressure situation, there is an
oil pressure relief valve. The valve helps to stabilize oil pressures,
but generally opens to prevent an over pressure situation, and closes if
the pressure drops, attempting to maintain the oil pressure. When parts
wear beyond certain limits, the pressure begins to fall, in spite of the
efforts of the pump and the oil pressure relief valve. That is the point
when you get the warning light when the engine is idling. The poor oil
pump simply can't keep up the pressure at that speed. This is a time
when an owner must decide what to do about an overhaul.

John Rodgers
88 GL Driver

Jeff and Tamara Nelson wrote:
>
> With all this talk about oil pressure I was wondering if someone could
> inform me of just what oil pressure is and how it is generated.  I know
> there is an oil pump and I think the spacing between the bearings and
> the crank/rods is involved but after that I'm guessing.
>
> Do the bearings restrict the flow of oil thus creating pressure?  Is the
> oil pressure measured in the crankcase or ?  You get the idea I hope.
> I'm just looking for a sort of oil pressure circuit diagram if you will
> or a Oil Pressure 101 class.
>
> Thanks as always.  If it wasn't for this list, I couldn't afford to keep
> my vans going...
>
> JN
>
> 86 syncro, 193K (his)
> 86 AT waiting for Tii conversion and big brakes (hers)