What was found
(CAN)ON TAKEOFF, OIL PRESSURE ON #1 ENGINE FLUCTUATED BELOW 40 PSI. WITH POWER LEVER AT FLIGHT IDLE AND CONDITION LEVER MOVING TO MINIMUM, OIL PRESSURE RETURNED TO NORMAL. WITH THE CONDITION LEVER TO MAX A ND POWER LEVER ADVANCING THROUGH 65 PERCENT TORQUE, FLUCTUATIONS REAPPEARED. POWER LEVER REDUCED BELOW 65 PECENT AND OIL PRESSURE STABILIZED. RETURNED TO AIRPORT WITH #1 ENGINE AT REDUCED POWER. OIL PRESSURE REGULATOR REPLACED.