I am surprised by the lack of replies here but there is no way that it should be able to reach 160 psi ! I am wondering about the relief valve in your oil pump.
since the oil pump is a positive displacement pump im inclined to say what releif valve
what goes in the pump must come out. if it cant come out a excessive build up of pressure occurs. hence the reason for the relief valve. since you were able to verify the readings, if it were me id start by looking into the pump and discharge lines and go from there.
