The Oil pressure Gauge on my Volvo 496 Mag starts to fluctuate as the engine approaches 4500+ rpm. Up to 4500 it runs @ 60 psi, once I hit 4500 it fluctuates between 40-50 psi, if I slow down below 4500 it steadys and returns to 60.
Anyone have any ideas as to the cause--this problem has just appeared this season.

Thanks