> > My warm idle pressure is around 30 psi. However, at speed it
> never exceeds
> > 40 psi (except when cold).
This sounds like the relief valve is opening. The problem is, both the
relief valve and the oil pressure gage rely on springs that can change
characteristics over time. In order to know which to change, you need to
verify the actual oil pressure.
The gage is what's known as a 'Bourdon tube' movement, it has a flattened
brass tube that is formed into a semi-circle. As the pressure inside the
tube goes up, the tube tries to straighten out, much like a garden hose does
when you turn on the water and have the end stopped. The end of the tube is
linked to the needle, so it deflects as the tube straightens. The problem
is, the brass work hardens over time and becomes stiffer, hence it doesn't
move as much when pressure is applied and you get a lower reading for the
same pressure. Found a decent diagram at
http://www.efunda.com/designstandards/sensors/bourdon_tubes/bourdon_intro.cf
m
Randall
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