I have a 64.5 Mustang 289 4bbl with the 4spd toploader. I just rebuilt the engine. Pretty well stock except for a very minor upgrade on the cam. The block had to be bored 30 over, new pistons, etc.. Everything went well; all specs followed. It runs great BUT....
When it starts it pulls a little over 30psi oil pressure with 10w30 oil. As it warms up the pressure drops to almost 0psi. The oil pump is new. All of the bearings were checked with plastigage and torques were triple checked.
This is...

Oil Pressure Issue