4.3L OIL PRESSURE

1996 CHEVY S-10 BLAZER/ START IT UP, RUNS FINE AND NO NOISES.  AFTER A FEW MILES THE OIL PRESSURE WILL DROP TO 0, AND THE ENGINE WILL GET VERY NOISY TOP AND BOTTOM. LET IT SIT FOR A WHILE AND IT WILL RUN FINE. ANY IDEAS. I KNOW THE OIL PRESSURE DOESNT STAY VERY HIGH ON THESE TRUCKS- BUT THIS DROPS TO 0. ????? OIL PUMP, DIST AND PUMP DRIVE SEEM OK.  

Likely worn engine bearings. It could be a stuck relief valve in oil pump but not too likely. You DO NOT want to drive it this way!!! If you are using 5w30 oil in it, drain it out now and try some 10w30 if you are where it gets down to and below zero a lot or 15w40 (not 10w40) 15w40 will boost oil pressure then most here. 5w30 can provide very low oil pressure in worn engines. Also there is not need to verify pressure with a manual gage as engine noise confirms lo pressure. BTW pressure can drop to 20 PSI or a bit less hot at a idle but not much below that in a tight engine. Cruising if you are above 35 PSI you are pretty safe.  

WELL I AM RUNNING 10W-30( I LIVE IN BUFFALO NY) THE TRUCK WAS RUNNING FINE BEFORE A HIGH RMP PASS ON THE HIGHWAY( NOTHING TO CRAZY-JUST PASSED SOMBODY) THEN THE NOISES STARTED SO I SHUT IT OFF, LET IT SIT. IT STARTED AS A CHIRPING NOISE. I THOUGHT THE FLY WHEEL WAS LOOSE. DIDNT SOUND LIKE A KNOCK. BUT AFTER RUNNING A FEW MIN IT STARTED KNOCKING AND TICKING. DEFINITLY NOT DRIVING IT THIS WAY. THIS ALL STARTED A FEW BLOCKS FROM MY HOUSE SO I JUST PARKED IT. IM A MECHANIC AND IVE NEVER HEARD OF THIS BEFORE. ANY IDEAS???  

Well high RPM pass before problems is a clue here. Could ne a intake plugged with sludge that broke loose on "pass" or you could have spun a bearing. I this stage before I made many suggestions as to problem I would "suggest" that you drop pan and inspect bottom end and inside of pan. If you are a mech you will know the smell of burnt engine bearings.