The oil pump turns more at higher revs, this is then producing more oil pressure, so when you change gear the revs are in a lower range so the oil pressure drops.
The oil pump supplies the oil to the engine bearings where it is forced from one to the other. That is what creates the oil pressure. The pressure is transmitted to the gauge by way of a sending unit. You need a mechanical gauge to see what the true pressure is so as to determine if the sending unit is bad. A defective oil filter relief valve will cause a pressure fluctuation. The pressure will increase from an idle as you accelerate. You will need to check and see what normal operating pressure is and at what RPM.
Clean the Filter!
I suppose. Was that the pressure when the filter was new of very clean? No 2 filters will be exactly the same.
This is what your filter gauge will read when it is first start with a new and clean filter cartridge / D.E. or sand.
It should do just the opposite. I would check that gauge.
change in temperature causes change in pressure
The pressure gauge will generally read 10 PSI higher than when the filter was clean. In any case do not let the filter gauge go above 40PSI.
It could be as low as 8, or 10, 12, the pressure could even be lower depending on your filter size, the lower the pressure the cleaner your filter media is the higher the pressure say 17, then you need to back wash or change the media, if you are not using sand.
Either the gauge or the gauge's sensor is broke. Has the oil & filter been changed in the vehicle lately?
Your gauge could very well be bad, many pools that we took care of the gauge on the filter was bad, after backwashing the filter just check any of you lines going back to the pool and your should notice the pressure is a lot higher. A lot of people just check the flow by placing there hand at an outlet to check pressure than by walking over too the filter and reading the pressure, instead of buying a new pressure gauge.
Usually the pressure gauge on your pool equipment indicates how much pressure there is before the filter. as the pressure goes up it indicates that the filter is getting blocked and needs a backwash or cleaning. while the pressure is low the filter does not need cleaning.
Pressure Indicator is any instrument that indicates pressure. Pressure Gauge is also a type of pressure Indicator. It is a mechanical device. Pressure indicators can work on mechanical deflection (in case of pressure gauge) or Piezo electric effect, change in capacitance, change in inductance etc. These are generally digital type instruments.