Oil pressure problem C-85

My mechanic has checked as much as he can without tearing down the engine. He cut open the oil filter and said there were no metal pieces inside. He checked the pressure relief valve and it was fine. He removed the oil tank to check the pickup tube for leaks and found none. He hooked on his own pressure valve and checked it against the one in the plane. They were identical. He checked the entire engine for leaks and found none. He wants to check the internal oil pump but feels he will have to remove the engine to do so. Has anyone had experience with this? Regards, Larry McCartin N93436

Yes, remove the oils pressure relieve value. It is posable it has a bit of something on it keeping it from seating.
Kevin

You might check for Metal in the oil screen/filter also check the oil pressure
relief valve (Ball) for something in the seat. I have one thing that happened
to me in an 0-200 engine, bad connecting bearing (2)..

In theory, two things are needed to create pressure. A pump that can provide the necessary pressure and volume, and a restriction downstream to maintain the pressure. If there is low pressure, one of those two is compromised. If it isn't the pump, or the gauge, and there are no external oil leaks that would relieve the pressure (that would be pretty obvious), then there has to be an internal failure of either a seal or a bearing. This would be consistent with higher pressure with a cold engine, and as the oil warms up and thins, the pressure drops. This isn't much help, I am afraid, but maybe gives some context.

My Coupe is a 415C with a C-85 Engine rebuilt with a 0200A new crank. While taking off Saturday I glanced at the oil pressure gauge which usually reads about 35 start to go down. I immediately returned to the airport to land. While on final the pressure was down to 5. Today my mechanic checked it and said the gauge was correct. Both his gauge and my gauge read the same. He is not sure what the problem is but doesn't think it is the oil pump. The gauge will read around 25 but as the engine warms up the pressure will start to drop until there is almost no oil pressure. The engine only has around 300 hours . If it's not the oil pump then what could it be? I'm open to suggestions. I invite your input.