My readings are very random but discovered that most likely is caused by faulty oil pressure sending unit (located on a right side in engine bay are). Very often it shows high readings while the car is warmed up. If I'll knock on it with screwdriver reading seams to come back to normal which in my case is about 1.5 while idleing.

 

I also had random readings (needle constantly jumping up and down). In my case it turned out that the wire inside the crimp connector at the oil sensing unit had come loose. It was a very easy fix, basically finding the wire in the engine bay attaching a new connector and re-attaching the connector to the oil sensing unit.
By the way: If I recall it right, when there's no connection then the oil gauge will read 5, not 0

 

Thanks for all the feedback. Need to check the wires to the oil sensing unit. It sounds like I have the same problem. Is there a video / instructions on how to do this?