Oil Pressure Gage and Sending Unit Revisited

The thermal design of the gauges “averages” ( integrates is probably a more accurate description) the voltage supplied to them, so they don’t jump around. I suppose the sender resistance could be jumping around at idle, I have never looked at one with an ohmmeter while running.

Do you have a good ground from your engine to the body of the car? Weird things can happen when you are missing a ground.