What is the primary result of using too low a viscosity oil in an engine?

Using an oil with too low a viscosity in an engine can lead to low oil pressure readings. Viscosity refers to the thickness of the oil and its ability to maintain a lubricating film between engine components. When oil viscosity is too low, it may not provide adequate lubrication at higher temperatures or under heavy load, leading to insufficient pressure in the oil system. This can cause a number of problems, including potential engine wear, overheating, and ultimately engine failure, due to insufficient lubrication.

Other options, while they may be related to engine function, do not pinpoint the primary issue that stems from low viscosity oil directly as effectively as low oil pressure readings. For example, while lower viscosity can sometimes lead to increased fuel consumption due to less efficient lubrication, the first and most immediate indicator of using the incorrect oil viscosity is the drop in oil pressure readings.