air compresses like a spring, oil doesn't. If the gauge is measuring pressure, Id like it to be all non compressible oil. It really measured 23 with the air bubble out of it and 20 with the bubbles. the air did make the gauge read more stable, ie when I bled it, the gauge would vibrate very slightly at idle. I picture a hydraulic jack pumping with air in the system, its not going to lift to its fullest potential (show highest oil pressure) if its compressing air instead of moving fluid.
