Hello, I have a 64 M20E with the IO360. It has 400hrs SMOH and 18hrs since IRAN (New cam, lifters, bearings, cylinders were reconditioned with new rings). I have been running Aeroshell 80 SAE 40 mineral oil for break in. I have original instrument cluster and a JPI 700 engine monitor with oil temp. When I start the engine I get 75ish psi at 1000rpm on the oil pressure gauge. When I push it up to 1500rpm the oil goes pressure goes up to mid 80s. At 2300rpm on the ground it goes to mid 90s. I have confirmed the pressure with a calibrated shop gauge. The pressure is in the green while I taxi and at takeoff power. once I level off I notice that the pressure starts to come down. In cruise I see roughly 55psi indicated at 24 squared. My oil temp is in the 180s per analog and JPI 700 gauges. I know that the vernatherm should be operating around roughly 180 to allow oil to flow to the cooler. The cooler was overhauled in 2011 before I owned it. The pressure relief valve has 6 washers (9 max per IPC) under it. I added a 7th washer but was seeing 115psi cold at 1500rpm. I did not want to go any hiring with the rpm. I opted to take out the 7th washer. I am going to remove oil cooler and flush out and see if that helps. Does anyone have any ideas on why the pressure drops like that?