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 identified above.

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.