As heating oil gets colder, its viscosity?

As heating oil gets colder, its viscosity increases. Viscosity refers to the thickness or resistance to flow of a liquid. When the temperature of heating oil drops, the molecules move more slowly and come closer together, which results in a thicker or more viscous fluid. This is a common characteristic of many liquids; as they cool, molecular motion decreases, leading to higher viscosity. Higher viscosity can affect the fuel's flow through pipes, filters, and nozzles, which is an important consideration in heating systems, particularly in colder weather.

Other options do not accurately reflect the behavior of heating oil as it cools. The viscosity cannot remain constant, as temperature changes inherently affect the flow characteristics. It also does not fluctuate in an unpredictable manner; rather, it consistently increases with a decrease in temperature.