1992 Other Holden Models LOOSING OIL PRESSURE

Engine Mechanical problem
1992 Other Holden Models V8 Two Wheel Drive Automatic 250000 miles

this seems to be a intermitant problem have replaced sender unit put high volumn oil pump on and drove 1200 kms no prob then one morning had no pressure left it next day fine have used 3 different oils replacd filter also put a guage on and will be fine and just stops hot or cold