Which issue could result from incorrect oil viscosity in an engine?

Using incorrect oil viscosity in an engine can lead to engine overheating. Oil viscosity determines how easily the oil flows at various temperatures and how well it lubricates engine components. If the oil is too thick (high viscosity) for the operating conditions, it can impede flow, leading to inadequate lubrication and increased friction among moving parts. This condition may cause the engine to run hotter than normal, potentially resulting in overheating.

Additionally, if the oil is too thin (low viscosity), it may not provide adequate protection or maintain a proper lubricating film, which can also contribute to excessive wear and overheating. Therefore, maintaining the correct oil viscosity is vital for optimal engine performance and temperature regulation.

The other options, such as improved fuel efficiency, increased power output, and a higher compression ratio, are not directly connected to issues arising from incorrect oil viscosity. These aspects are influenced by various design and operational parameters rather than the viscosity of the oil used in the engine.