oil prssure lit comes on when engene reaches running temp

Hello, Did you change the oil filter as well? The chatter tells me that you really are losing oil pressure, but the change in temperature makes this sound more like a bleed-off issue. As oil heats, it becomes thinner. The other part of that is that the oil pump has a pressure relief valve that may be bleeding off pressure. If you have a ton of miles or wear on your engine, the bearings and journals may have sufficient clearance to drop oil pressure when the engine is hot because it simply cannot be pumped fast enough. Engine flush is a good first step, make sure the filter was changed, especially after the flush, and ensure that you are running the appropriate grade of oil according to your climate and operating conditions. If this engine is suffering from water intrusion due to the severe weather on your coast, was the engine oil flushed and changed before it was started the first time?