BE-30 pilot reported the oil pressure indications of one engine fluctuated between normal and abnormal. The pilot shut down the engine; diverted and made a precautionary landing. After adding more oil to the engine; the pilot departed and completed the flight safely.

Narrative

During a normal departure from the ZZZ1 airport on my third leg of the day in a King Air 350 aircraft with 130 hour Blackhawk engines; I started to notice a fluctuation in my right hand number 2 engine oil pressure. I was climbing out of about FL200 at the time. It would bounce into the red and then immediately come back into the green. During these fluctuations there were no other engine indications out of the ordinary. All other parameters were in the green and operating normally. I continued to monitor the gauge while suspecting a transducer problem as all the other indications were normal. A few minutes later the oil pressure indicator fluctuated back into the red and stayed in the red region for a few seconds. I reduced engine power on that engine and the pressure indication came back into the green. There was still some erratic movement of the gauge but it was staying in the red more than in the green. At this point in time I advised ATC that I would need to divert back to ZZZ2 as that was the closest suitable airport from where I was at the time. ATC cleared me back direct to ZZZ2 and gave me a decent to a lower altitude. As I made the turn and started the descent I pulled the affected engine back to idle. It came back into the green momentarily but would still fluctuate back into the red at times. Still all other engine indications were normal. Being that I could see the ZZZ2 area and had plenty of altitude and no other abnormalities and out of an abundance of caution to protect the engine I made the decision to shut down the right engine.I then [requested priority landing] to ensure that I would get priority handling into the airport. I made a right downwind approach and landing on Runway XXL. The approach and landing were normal and uneventful and I was able to clear the runway and taxi into parking on my own. I felt very sure it was an indication issue but out of precaution for preserving the engine I made the decision to shut down the engine and land as soon as possible. After landing I spoke to my Director of Maintenance who advised that I check the engine oil quantity as that can sometimes lead to Oil Pressure (OP) fluctuations. I did and it was between 3 and 4 qts low. Not super low for a P&W PT6 engine but we decided to bring the level up to 1 quart low and test run the engine. I did and the test run was completely normal. I was then advised that the aircraft should be safe to fly home. I loaded up and we flew back to ZZZ3 and the flight was completely uneventful. All engine indications were normal.