classic kev said:

An iffy sender is possible, the best way to check would be to get an oil pressure test gauge with the right adapter to screw in to the oil pressure switch port. A mechanical gauge should be the most reliable indicator.

The workshop manual sets out the following:

Disconnect battery, remove oil pressure switch.
Fit test gauge
Reconnect Battery
Start and run engine to normal temperature
At 2400rpm min. oil pressure should be 1.76kg/cm2
If no oil pressure check for air lock
If pressure low, overhaul pump.

According to the manual, the pressure test equipment is LRT-12-052 but a generic tester should do, a quick Google of "oil pressure test kit" shows a variety of kits available with an equal variety in price and quality.

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just wont start said:

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Hi, just so you know, i borrowed a pressure gauge and it showed about 38 psi and dropped a few when warm so all was good, turned out to be both gauge and sender that was at fault. for interests sake i took the lid off the old unit to see how it worked, the oil pressure moves a pin onto a rocker that is connected to a pick up arm moving on a wire coil, just like a small fuel sender. Photos attached.

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