Low Oil Pressure when warmed up

[ALS85GT]

I have a nagging issue which is when my engine reaches normal temp, 180-190degrees, the oil pressure drops to about 8-10lbs. When cold it is around 40lbs. I have replaced the oil pres guage so that's not it. I have tried dif weights of oil, now using HD40. I have tried diff oil filters. I have an oil cooler on the car but can't use it cause I'll get 0 oil pressure???!!(when cold).- the oil pres will raise when reving the motor so I think the oil pump is working. Its also brand new.- Brief history on motor; 86 block, stock lower end, ie all bearings etc. Not sure on number of miles. Cam bearings looked used but not shot so those where retained. 85 rebuilt heads fm a carbed mustang.---I don't remember if the oil pump pickup uses a gasket between the pump and the filter? And I don't rem if I put one there. I think it should use one.
What do you guys think? Thanks for any thoughts.-one other thing. Even w/the low oil pressure, oil still gets to the top cause I checked it while running....


[This message has been edited by ALS85GT (edited 10-17-2001).]