How can you verify the quality of engine oil?

Checking the quality of engine oil primarily involves assessing its color and viscosity. Clean oil usually has an amber or golden hue, indicating that it is still effective for lubricating the engine components. Viscosity refers to the thickness of the oil, which is crucial for ensuring it flows properly and provides adequate protection against wear.

If the oil has turned dark, appears gritty, or has a consistency that is noticeably different from what is expected, it may no longer perform effectively. This degradation can occur from contaminants or the breakdown of the oil's additives over time.

The other methods mentioned are not reliable indicators of oil quality. Smelling the oil may not provide clear information about its condition, as many odors can be misleading. Shaking the oil can does not offer any concrete evidence regarding its quality, and checking for bubbles does not provide insight into its overall performance capabilities. Thus, assessing color and viscosity is a much more effective and practical way to verify engine oil quality.