i have a chevy silverado 94 4x4 with a z71 motor and my oil pressure is going from 60psi to 40psi to0psi . I checked the oil and there is no water in the oil and the oil cooler lines have oil through them. Anyone ever have this issue?

 

how often does this happen? does it drop at idle, or while driving? i would suspect a bad oil pressure switch. less than 20 bucks at parts stores, less than half hour to change. it should be right behind the distributor. otherwise, it could be clogged oil passages inside motor, or worst case a bad oil pump.