low oil pressure. please help!!

i have a 90 k2500 with s 350 in it. i noticed that my oil pressure would drop after engine warming at idle to 0 psi. cold start i would have around 50 psi. was told that stock gauge needed replaced with manual one. replaced, same problem... then i was told maybe i had a weak oil pump. so i pulled motor and replaced oil pump with a high volume pump... to my dismay, i still have the same problem...driving down the road my oil pressure is around 30 psi. when i slow down or come to a stop that is when it drops around 0 psi. engine does not give any indication of oil starvation and runs very good. no signs of low compression either. does anyone have any advice on this problem...i am at wits end here. thanks

when you replaced the stock gauge did you use the same sending unit? or did you tap into the oil pressure with a pressure gauge? if you used the same sending unit my guess would be it is a bad sending unit. Howver if you tested the oil pressure with a pressure gauge in place of the sending unit, i would wonder if there could be a partial clog in the oil gallery leading to the sending unit. I would think if you were actually getting no oil pressure you would hear it, or the oil pressure switch would deenergize the fuel pump do to low oil pressure, you could also try measuring oil pressure at the oil pressure switch if you are getting nothing tapping into the sending unit hole

Replace the oil pressure sending unit. It's a cone-shape item hanging near the oil filter. I had this same problem and have seen it happen to others (the is another recent post on here where this was the exact problem and remedy.)

If you have done what the previous posters have recommended I would say that you have some worn out bearings.

What brand of oil and oil filter are you using?

I would say from what you are describing you have a very high mileage engine. The bearings are wearing a lot, and that extra clearance allows the oil pressure to drop. (pressure is defined as resistance to flow, the less resistance i.e. more bearing clearance, the less pressure). Also the hotter the oil gets the thinner it gets, also creating less resistance to flow. A simple but temporary cure would be to step up the grade of oil you are using to 10W-40 or even 20W-50, and then re-build the engine.

thanks for the info guys.....the only conclusion i have came to is worn out bearings. guess its time for a rebuild