oil pumps (not efi)

[Dave Williams]

-> moving parts separated under higher loads.  That's why heavy grease,
-> and not 5W15 oil, is used in wheel bearings.

 Rolling element bearings are in contact by definition.  The lubricant
is mostly for the benefit of the bearing cage.  The grease in a wheel
bearing does not physically separate the load surfaces like on a plain
bearing.


-> 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.

 The pistons contribute little heat to the oil of most engines.  A few
turbocharged gas engines and some Diesels spray oil on the underside of
the piston for cooling, but the majority of engines depend on contact
with the relatively cool cylinder wall and the cool intake charge.  Dry
sump engines, such as Harleys and some other motorcycle and many racing
engines, don't put enough oil in the crankcase to cool much besides the
bearings.  Plain old oil shear in plain bearings can raise the
temperature of the oil in the journal to over 300F under racing loads,
even on relatively low output engines.