oil pressure issues
 

okay folks have a 96 G20 305 engine 4l60 trans it has 40 lbs oil pressure at start up cold as it warms up it drops to almost nothing--at idled has nothing redzone on the factory gauge--did put in a mechanical gauge for a short time figuring the one from factory might be wrong--I have changed the oil pump high volume one-went from factory recomended 5-30 to 10-40 oh heck no--went to 10-30 ran it about 2k miles --went back to 5-30 all seems the same--have heard from some mecahinics that if the valve tappets were out of adjustment it would run low on oil pressure??? the man I got the van from had a rebuilt motor put in it said from day one no oil pressure at idle--it does click upper end noise at idle --I'm stumped --actually been a Ford truck guy since 78 looking for help from you Chevy guys --I like the van just really worried it's gonna grenade on me --HELP plaese:confused:

Since you are saying that this has been an issue since the rebuilt motor was put in, I would say that it could be a cam bearing, or other internal issue. I have read a few posts about rear cam bearings being the wrong size and leaking internally. If the assembler didn't measure them and just installed them out of the box there could be an issue.
Also, I found more posts saying not to install a high volume oil pump, ans that could cause failure of the pump drive.

The SBC engines put out low oil pressure at idle, as a norm...but you want to make sure you have enough, of you will burn it up.