What is the most likely cause of excessively low oil pressure?

Excessively low oil pressure is most commonly linked to worn out rod and main bearings. As these components deteriorate over time, the clearance between them and the crankshaft increases. This added clearance allows oil to flow too freely, preventing sufficient pressure from building up in the oil system. The oil pump struggles to maintain the necessary pressure due to the reduced resistance provided by the worn bearings, leading to an overall drop in oil pressure.

In contrast, while overfilled oil sump, clogged oil passages, and thick oil due to low temperatures can affect oil pressure, they are less likely to be the primary causes of a significant drop in pressure. An overfilled sump might lead to aeration of the oil but typically does not create a drastic decline in pressure. Clogged passages can restrict flow but usually result in higher pressure in localized areas, not a broad drop in pressure. Thick oil in colder temperatures can create initial resistance to flow, but as the engine warms up, the oil thins and flows more easily. Thus, worn bearings represent the clearest and most direct reason for a consistent low oil pressure reading.