One of the advantages of always flying the same airplane is that you should have a very good feel for where the needles sit and so if there is a noticeable change then it should be relatively obvious. If you are flying club airplanes then this obviously is harder to do as you will likely be flying a different air frame every flight. Nevertheless it is worth paying attention. I would not continue flying an airplane that had oil pressure that varied with engine RPM even if the pressure stayed in the green. As Pilot DAR pointed out the oil pump should have more than enough output to hold the oil pressure steady in the green at any normal operating RPM ( eg anything above 1000 RPM or so). There is something wrong that should be investigated.
One thing that I have noticed in light aircraft pilots is that there seems to be a poor practical understanding of the relationship between oil temperature and oil pressure. With cold oil I expect to see an oil pressure near the top of the green at initial start up with the oil pressure dropping to the normal steady state value for that aircraft as the oil warms up. If I have to do a prolonged climb I expect the oil temp to rise and see a slight drop in oil pressure with the hot oil losing some viscosity. I don't want to see oil temp close to the red line so I would take action to reduce the oil temp if I were to see this. Anything that did not conform to this, like for instance low oil pressure with cold oil would merit investigation
In a related topic oil consumption is an important indicator of engine health. A sudden rise in oil consumption is almost always the engine telling you something is very wrong. I once had an engine failure in a heavily loaded Piper Navajo. The choice was fly 100 nm over mountains to the nearest big airport or land at the small airport I just took off from. This involved an NDB approach to minimums with a circle to land, which was I elected to do. To say it was a "significant emotional event" in my flying career would be rather an understatement....
Anyway it turned out 2 other pilots had put a total of 4 litres of oil in that engine in the last 6 hours and did not think it worth informing maintenance
This was a totally avoidable failure
