When the RPM reaches 2800 and over, the oil pressure gauge starts fluctuating erratically. The engine works fine and the gauge shows normal pressure at RPMs lower than these. What might be causing this?
The fluctuating oil pressure indicates an inadequate oil supply to the oil pump. It is possible that there may be some trash or sludge buildup on the pickup tube screen limiting the oil supply at the oil pump. An engine flush with a flushing agent may correct the issue with the next oil change. If this does not correct the issue, the pan will need to be dropped and the pickup tube and screen inspected. Also the clearances in the pump should be checked. You may want to enlist the help of a mechanic, such as one from YourMechanic, who will be able to accurately diagnose this fluctuating oil pressure issue.