Some general observations on this oil pressure thread:
Gauges: I have yet to see a mechanical (Bourdon tube) pressure gauge fail,
although as you can imagine, a plumbing leak in the capillary tube from
engine to dashboard can be quite spectacularly messy. Regarding electrical
ones, the gauge reliablity seems as good as the other electrical gauges,
but the sending units (including idiot-light switch units) are another
story. Their installation on the engine block is a rough part of town, and
they often spring leaks, leading to false low-pressure readings and embar-
rassing puddles. When low pressure warnings are noticed, my first step is
to inspect the sending unit and swap in another if it looks doubtful. Most
of the time, that will fix it.
Oil Pumps: These fail progressively, not abruptly with a *bang*. If they did,
there would quickly be a much louder *BANG* from the engine and we would have
a lot more dead old cars at the side of the road. Symptoms of a worn oil pump
include only fair cold oil pressure, which plummets when the engine warms up.
I will venture to say that despite what the manuals may say, you should NOT
have a steadily-glowing warning light at idle. Increasing engine speed should
bring a near-instant gauge response, not a slow creep upwards. An engine at
highway speed should have an impressively-high oil pressure, not a lukewarm
35 or so psi. BTW, our 128K '72 Pontiac that I mentioned yesterday has a new
pump installed now, and with no other changes is putting out a healthy 70 psi
at cold idle and 60 at driving speeds.
Bearings: I think the role of worn bearings on oil pressure is a tad over-
stated, and this is partly my fault for talking about them yesterday. Agreed,
loose bearings could lower the pressure somewhat, but I think they would have
to be awfully bad, and you would be investigating an assortment of bad noises
by that time. If the engine sounds good overall, I'd check sending units and
pump first. Throw in a new pump if necessary, and if you still have to rebuild
the engine after that, at least you've already got a nice new pump to protect
your rebuilt engine.
Andrew C. Green
Datalogics, Inc. Internet: acg@dlogics.com
441 W. Huron UUCP: ..!uunet!dlogics!acg
Chicago, IL 60610 FAX: (312) 266-4473
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