Recently re-built my 97 1FZ, head completly rebuilt, new rings (factory not oversized) rod bearings, oil pressure sending unit, and other wear parts that don't reflect oil pressure performance. At Start up the factory gauge runs to the high side of the scale, after warm up to operating temp the oil pressure drops to O-s***. Anything above idle (600 RPM) the pressure increases to "normal" pressure range at hwy speed, (1800 RPM +) back to high side of the scale. I did not open up the factory oil cooler or replace the oil pump. I have put 8,000 miles on the rebuild and changed the oil twice, using 10-30 oil with a Factory filter. Any thoughts on the Huge change in oil pressure ?