I have Livorsi2/Gaffrig2 guages. But maybe a mechanical gauge would be good.

The VDO gauges on my 357 show 30 PSI. A high quality mechanical gauge shows 60 PSI. New senders didn't change the reading. If you have put 50 hours on the boat and the motors haven't failed than you have enough oil pressure for what you are doing.

140-92=48hrs Don't fix what's not broken.

Oil system is the part of an engine I know the least about. I have rebuilt a one boat motor ( vortec 350) and a few car motors. I can assemble engines pretty well but I feel like the oil system is where marine motors really differ from cars. Just trying to make sure I am ok.

I barely had 40psi and then changed the sender and suddenly have 70psi. I suspected the sender because the guage was working "sticky".

yes if it has been the same and has not failed you will find a bad reading most likely, it would have failed within 5 hours if it was an issue...

I wonder if my gauge is right. The oil is either at 20ish or 40ish. It does not seem to move smoothly with rpms.

Use 20-50 or perhaps straight 40 w synthetic, watch your pressures rise. My 32,000 mile Harley likes straight 60W and just passed inspection for extended warranty coverage. In a few years I'll switch to 70W but only because it usually above 80 when I get to ride. Would it be better to rebuild the engine, sure, but as long as the pressures hold I want to rack up the miles.

But you need to double check with true mechanical gauge FIRST. As the pressures could already be fine.

For me it was a bad sender sending sketchy signals to the guage. Now it moves smoothly. $26 from Amazon.