Chevrolet Repair: z24 low oil pressure at idle, worn bearings, low oil pressure

Question
we have z24 chevy 1988, the gages look fine at initial start up - after it runs for about 6 miles- the low pressure oil light flashes and the check gauges light comes on. This happens only when sitting still at a stop light. when the accelerator is pressed the pressure goes up. we replaced the oil pump. what could be the issue? should the oil pan gasket be replaced - does it effect oil pressure.

Answer
Hi Laurie Hitze,

Right off I suspect the bearings are worn.  Worn main and rod bearings cause a larger space between the crankshaft and the rod and main caps.  

Could also be a worn out oil pump.  If it is bypassing too much or worn out gears it won't keep up.  But since it is ok at start up, that is tell tale worn bearings.

Good news:  This can be a simple fix.  Since you are talking about the oil pan anyway, if you drop that, you can change the oil pump and bearings while you are under the car.  You loosen the main bearings, but don't take all the caps off.  You take them off one at a time.  One half of the bearing is in the cap, the other needs to be pushed out by feeding it around the crank.  Put the new one the same way.  Once all the caps are replaced, retighten the caps to torque specs.  The same is for the rods.  Use the same size bearing you remove.  It is worn and so is the crank.  By replacing the bearings, you tighten the gap back up.  Enough to provide a decent amount of pressure.  Bearings cost about $50.  Oil pump should be new at this point, and use a high volume.  This whole job should cost you under $200 and a weekend.  

C J S