4.3L oil pressure issue

[Muddytazz]

My father-in-law gave me his old 89 S15 Jimmy to fix up and sell. Only thing I can find wrong with the motor is the oil pressure. You start it up and you have nice good pressure(about 65), but after you drive for about 45 min, the pressure has slowly dropped to "0". Shut the rig off for about a min, start it back up and you have full pressure again and can drive for about another 45 min when you've lost pressure again. Any ideas?

 

[big83chevy4x4]

my cousin had a similar problem in his 88 4x4. it would be at 40 at start up and gradulally go down to 0 when warm. if you let it set a while, and start it again, it would have oil pressure.
when we pulled the motor, i pulled the pan off and the oil pickup was laying in the botom on the pan. with the deep sump, the oil was away from the oil pump.

 

[Muddytazz]

Hmmmmm, so far sounds like it might be an easy fix. I know this motor doesn't burn any oil and doesn't leak any either.