Originally Posted by CurtSmall

I haven't had this issue with my BMWs, but I had the exact same symptoms on a 93 Range Rover I used to drive. In my case, it was the main bearings on the crank. When the oil was cold, the oil pressure was above the sensor specs, but as it heated, the worn bearings could no longer maintain back pressure thru the journals in the crank. The engine had no knocks or noises to indicate worn mains.