The pump develops only sufficient pressure to overcome the resistance of the
system it is supplying. Installing a new pump in a worn engine may increase
the pressure slightly, because internal leakage in the pump will be less,
but it will not bring the oil pressure back to spec. Oil pressure is a
function of system resistance, which is a function of the velocity the oil
flows at through all the oilways. Thus, at idle, the pressure is quite low
and as engine speed increases the oil pressure will increase up to the
pressure relief valve setting, which is 70 psig on the TR3, I believe. As
engines get worn, the clearances in the engine open up to such an extent
that the resistance seen by the oil is reduced, to the extent that the PRV
setting is never actually reached, hence oil pressures of 45-50 psig on the
highway. I would not buy a TR3 with such an oil pressure at highway speeds
WHEN WARM (pressure is also a function of temperature) without being
prepared to rebuild the engine at some point in the future. Having said
this, my TR3 had 50 psig when warm when I bought it 10+ years ago, and it is
still running strong, although I did replace the big end bearings right
away.
-----Original Message-----
From: Radley, Jack <JackR@SHRIVERCO.COM>
To: 'triumphs@autox.team.net' <triumphs@autox.team.net>
Date: Thursday, April 08, 1999 9:15 AM
Subject: Oil Pressure - follow up
>
>What does the oil pressure gauge measure? If it is oil pressure right
>off the pump, what does that have to do with the condition of the
>engine?
>
>If you have an engine that is 100 miles from blowing up, but that has
>had a new oil pump installed wouldn't you expect to get good pressure
>while at the same time you are driving a time bomb?
>
>Do the differences in the tolerances found in a new engine compared to
>the tolerances found in a worn out engine affect oil pressure? Is the
>oil pressure gauge affected by the back pressure of oil being pumped
>through the tighter tolerances of a new engine?
>
>I'm just sort of stuck on this. If the gauge reflects pressure right
>off the pump, then engine condition would seem irrelevant - unless some
>sort of back pressure comes into play.
>
>Jack Radley
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