I have been thinking about this post and would like to contribute an

idea.  What may be happening here could have nothing to do with hardware and
everything to do with rheology.  Many common fluids are Newtonian; that is
to say their viscosity is constant with regard to shear rate.  However,
others, such as polymers, are non-Newtonian and exhibit a reduction in
viscosity with regard to shear.  Single grade oils and multi-grade synthetic
oils are pure substances and therefore Newtonian.  But multi-grade mineral
based oils achieve a viscosity range by adding a polymer to the oil base.
This may transform the oil to a non-Newtonian fluid and could exhibit shear
thinning.  When the wall shear stress builds sufficiently, this has a
tendency to cause a flow disruption.  In extrusion of polymers it is called
melt fracture and is accompanied by wild fluctuations in pressure and flow;
essentially a chaotic system.  This phenomena is often accompanied by rather
distinct changes in the sounds produced by the process.  This sounds a lot
like the description of the oil pump issue.  If true, it would require
standard mineral based multi-grade to make this happen and not with single
grade or synthetic grades.

Just an idea.

Charlie Smith
KIS Cruiser 4021

William wrote:

Charlie, Good observation -- I hadn't considered Non-newtonian fluid
behavior before.
Bill Schertz
KIS Cruiser # 4045

 
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