Need info on 251 engine

[Michel D]

Ok dose some one no what could make the oil pressure on my engine fluctuate 10 to 15 psi!
I no that my gage is ok.
it is not the oil filter.
The oil pressure starts at 45 psi cold and start fluctuating between 35-45 psi. and more the engine warms up the pressure goes down and down!

May be the oil strainer is taking some air!