I'm flying a Pazmany PL-2 with 0-290D2B, 810 hrs SMOH. A year ago, due to low oil pressure, I added washers to the max number, and oil pressure rose to normal level. Was using PhillipsXC10-50 and oil pressure stayed in green without a problem. Recently changed oil and am now using AeroShell15-50. Oil pressure on start and climb out is in the high green. But after flying for 30-40 minutes at 2300rpm, oil pressure approaches the top of green. Oil temp remains in green. When power is lowered, oil pressure goes down to middle green. Question, is this difference caused by the change in types of oil? Might there be a problem with the gauge readings? Or any other ideas? Thanks.