Which characteristic of aircraft engine oil helps it circulate effectively?

The characteristic of aircraft engine oil that helps it circulate effectively is primarily its viscosity and density. Viscosity refers to the oil's resistance to flow; oils with the appropriate viscosity can move through the engine's lubrication system efficiently, providing the necessary lubrication to reduce friction between moving parts. This is particularly important in an engine, where temperature and operational conditions can vary widely, affecting how well the oil flows.

Density also plays a role, as it influences the weight of the oil, making it suitable for the operational demands of the engine without becoming too thick at low temperatures or too thin at high temperatures. Together, these properties ensure that the oil can maintain its protective qualities over a range of operating conditions, allowing it to effectively reach all components that require lubrication and cooling.

Other options provided do not focus on the properties crucial for effective circulation of engine oil. Lightness and heaviness lack specificity about how they are defined in terms of viscosity, while chemical stability and filtration speak more to the overall longevity and cleanliness of the oil rather than its circulation ability. Color and odor have no correlation to the performance of the oil in the engine's lubrication system.