oil pumps (not efi)

[Ken Mayer]

On Sun, 15 Dec 1996, Stephen Dubovsky wrote:

> >It takes a finite amount of time for heat to transfer from on thing
> >to another.  The greater the temp difference, the faster the transfer, but
> >it is still a finite about of time.  

True.

> Im not so sure thermodynamics and heat transfer agree w/ you here.  I
> imagine it might happen at SOME speed, but you would be pumping oil so fast
> that it would be heating your bearings instead of cooling them...

Also true.

There seems to be a misunderstanding about how heat is generated in
bearings.  In a "plain" bearing, there is no metal-to-metal contact
between the rotating shaft and the bearing.  They are separated (ideally) 
by a film of lubricating oil.  The motion of the rotating shaft generates
a shear force in the oil film.  The "friction" within the fluid is what
generates heat.  The amount of "friction" is measured by viscosity.  Lower
"friction" >> lower viscosity >> oil "flows" more easily.  The reverse
tends to hold for film strength.  Higher viscosity tends to keep the
moving parts separated under higher loads.  That's why heavy grease, and
not 5W15 oil, is used in wheel bearings.  The result is an engineering
tradeoff to select a viscosity that flows reasonably well but which can
also maintain a reasonable film strength.  Also, nobody mentioned that the
circulating oil is splashed against the bottom of *very* hot pistons in
order to cool them.  Most of the heat in motor oil comes from contact with
the hot pistons. 

As for pumping oil so fast that it would heat the bearings instead of
cooling them, it would occur, but not at the rates the oil circulates in
an engine.  This effect is true high-speed friction.  As an example, when
air flows past the Concorde in supersonic flight, the skin of the airplane
heats up so much that the length of the airplane increases about 3
inches.  The skin temperature rises several hundred degrees above the
ambient air temperature.  During low-speed flight operations (takeoff and
landing), the skin temperature is the same as the ambient air.

Ken
:-)
(yes, I admit to being an engineer <g>)