Hello, Healeyphiles -
Before the thread on the oil pressure relief valve gets too cold, I wanted
to provide some information I received via communication with an instrument
engineer at Autometer (http://www.autometer.com) concerning the function of
the restrictor hole in the oil gauge line and the advisability of "bleeding"
the air out of the line.
While this is unlikely to put this issue to bed for all time, I thought it
would be helpful to have the input from someone who is actually in the
business of designing instruments.
According to the engineer, restrictor holes are normally built into
high-pressure sensing gauges to prevent damage due to dumping pressure into
them all at once. For the restrictor in the relatively low-pressure oil
line on Healeys, he says it would help to prevent the gauge from registering
varying oil pressures from the pump at low engine rpms. As far as the need
to bleed air out of the line, he says it is not necessary. As a matter of
fact, the line will "re-air" itself each time the engine is shut down due to
drain-back of the oil into the engine. Combined with the lack of vacuum
relief, the restrictor hole will help to slow down the drain-back, but if
the car sits long enough some oil will drain and will be replaced with air.
At higher engine rpms, any air in the line acts just as a shock absorber and
will dampen pressure pulses from the pump.
Happy Healeying!
Steve Byers
HBJ8L/36666
BJ8 Registry
Havelock, NC USA
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