Oil pressure varies depending
upon the specific oil's viscosity, its temperature, its
ability to hold to its viscosity under high temperature and
stress conditions. Also the oil filter must be clean -- not
clogged -- to allow oil to flow freely.
Oil pressure also varies
depending upon the conditions of the internal engine parts.
An engine with high mileage has worn to some degree. That
means there will be likely be larger clearances between
bearings and their respective parts. That is where oil
flows. For example, a high-mileage engine will have larger
clearances (gaps) between its rod bearings and the piston
rods than will a low-mileage engine.
The engine with larger
clearances will allow oil to flow more freely than the
lower-mileage engine with less wear (smaller gaps). Freer
flowing oil results in lower oil pressures.
Another factor affecting oil
pressure is engine speed. Many engine oil pumps a driven
directly by a gear mechanism that varies only with engine
speed. The faster an engine is operating, the more oil will
be pumped through its passages, and therefore, the higher
the pressure will go until it is relieved by a pressure
relief valve built in the oil pump.
The oil pressure light is a
precisely exact or nearly exactly an on / off type of light.
The pressure sensor at the engine's oil line has a threshold
of on / off, and switches the dashboard light on and off.
The specific condition --
either on or off -- of the oil pressure sensor will change
with oil pressure which is dependent upon the factors
So, if the sensor's threshold
is just about at the same point where an engine's oil
pressure is at a given time, the light will go on and off --
and could right at that oil pressure threshold -- flicker.
Oil pressure may be increased
by using the higher manufactured oil viscosity.
There is little that may be
done to influence oil pressure or when the oil pressure
light comes on and goes off, other than using a
manufacturer-approved higher viscosity oil, ensuring that
the oil filter is clean, and verifying that the oil pressure
sensor is operating correctly.