The oil pressure is governed by both the power of the oil pump which
increases with rpm being driven at half engine speed and the bearing
clearances (I think). As the bearings wear the clearances increases and
pressure drops.
Yes, there comes a point when too much oil pressure is not only required but
can be a bad thing (Lotus 1585 twin cam never liked a lot of pressure).
However, too low a pressure, especially when the engine temperatures are
high, can result in a break down of the oil film - resulting in damage. With
low oil pressure (I think) the film can break down more easily. A higher
viscosity oil will break down (the film) less easily at high temperatures but
can make the pump work harder when the oil is cold because the oil is
thicker. A thing about multigrade oils is that the two numbers refer to
respective viscosity at different temperatures - I think that is the
simpliest summary I can manager without running to 2,000 words. Here is the
advantage of the 5/50 and 15/50 Mobil 1 synthetic as oppose a 20/50 which is
actually thicker at a cold temperature while not getting any thinner at the
top end (50). A synthetic also does not break down at very high
temperatures, as found in turbocharger centre bearings and extreme operating
conditions (maybe low oil pressure and high engine temperature). I don't
think STP does any harm to an engine with low oil pressure unless it increase
the viscosity at extreme low temperatures (like in the Artic circle?). Some
additives, not sure about STP contain additives that do more than just
increase viscosity and protect bearings when the oil film either breaks down
(ZDDP?) or prevent the break down (Teflon?).
Daniel1312 - who has seen an engine with STP almost go off the gauge on a
cold start!
In a message dated 23/10/99 19:23:01 GMT Daylight Time, jboatri@emory.edu
writes:
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