What is typically a sign that an engine requires oil change?

An engine requiring an oil change often manifests signs that can affect its overall performance, one of which is reduced power output. When the engine oil becomes old or contaminated, it loses its ability to effectively lubricate the engine components. This can lead to increased friction between moving parts, causing the engine to work harder and ultimately resulting in a noticeable decrease in power performance.

In addition, degraded oil may not adequately clean engine parts or dissipate heat efficiently, further contributing to a loss of power. Keeping the oil fresh helps to maintain optimal performance and fuel efficiency, implying that regular oil changes are essential for the engine's health.

The other choices do not directly relate to the engine oil's condition or its need for a change. Deep blue exhaust smoke can indicate incomplete combustion or other issues, while low fuel consumption and a high compression ratio generally point to different engine characteristics or efficiencies rather than oil quality.