One of the biggest misconceptions about oil pumps centers around oil pressure.
As this video from Melling explains, oil pumps don’t produce oil pressure. They flow a particular volume of oil, which is then regulated by a valve within the pump. This valve determines the maximum oil pressure the pump can deliver.
Oil pressure is the byproduct of multiple factors that create resistance, including restrictions in the oil passages, the weight of the oil, and critical clearances within the engine. According to Melling, bearing clearances have, by far, the biggest effect on oil pressure. Check out the video below for a nifty demonstration of how the main bearing clearances affect oil pressure.