Hey my oil pressure guage is dipping and surging. Its normally at 40 or better, but it was at 0 earlier so I rode around the block and turned it off. My mechanic told me to listen for a knock that would mean that the oil wasnt circulating in the engine but I didnt hear one. Is this merely the guage acting up, or should I have the sending unit replaced?

That'* the gauge acting up. If you have zero oil pressure you would here it tapping.