Slow gauge

67Dart273 said
I would suspect debri or a restriction in the copper line "for start" If you can get clear (white) nylon, buy a length of it and a couple compression ferrules and temporarily hook that to the gauge, even if you remove the gauge. Then you can SEE the oil back and forth in the tube.

Also some gauges have a restriction right at the gauge fitting, and maybe something plugged it or it is defective.

I like the suggestion something might be blocking the line or inlet aperture of the gauge. I had an oil sender, which read alarmingly low. It turned out PO had used Teflon tape on the sender threads and a Teflon tape booger was blocking the sender inlet.