As a subject matter expert in the field of petroleum products, I can provide a comprehensive response to your question regarding the temperature at which oil gels.

Oil, in its various forms, is a complex mixture of hydrocarbons that can exhibit different physical properties depending on the temperature and composition. The term "gel" is not typically used to describe the behavior of oil, but rather the term "waxing" or "gelling" is more commonly employed. This phenomenon refers to the process where the paraffinic components of the oil begin to crystallize and form a network, leading to an increase in viscosity and a change in the physical state of the oil.

The onset of gelling in oil is influenced by several factors, including the type of oil, its paraffin content, and the presence of additives. For instance, #2 fuel oils, which are commonly used for diesel engines and home heating, do not freeze in the traditional sense but can begin to gel or thicken when temperatures drop below a certain point.

The reference to the temperature of 32°F (0°C) is a critical threshold for many oils. At this temperature, the fuel can start to become "cloudy," indicating the presence of wax crystals forming within the oil. However, it's important to note that this does not mean the oil has completely gelled or solidified. The oil can still flow, albeit with increased resistance and viscosity. This cloudiness is often the first sign of the gelling process and can be a precursor to more severe gelling at lower temperatures.

As the temperature continues to decrease, the gelling process intensifies. The wax crystals grow larger and more interconnected, forming a more solid structure within the oil. This can lead to a significant increase in the oil's viscosity, making it difficult for the oil to flow through pipelines or fuel systems. In extreme cases, the oil can become so viscous that it effectively solidifies, impeding the operation of engines and heating systems.

To mitigate the effects of gelling, various strategies can be employed. These include the use of additives that lower the pour point and cloud point of the oil, thereby delaying the onset of gelling. Additionally, heating systems can be used to maintain the temperature of the oil above the point at which gelling occurs. In some cases, selecting a different type of oil with a lower pour point can also be a viable solution.

It's also worth mentioning that the gelling process is reversible. As the temperature increases, the wax crystals will melt, and the oil will return to its liquid state. However, the extent and speed of this reversal depend on the specific properties of the oil and the temperature to which it is exposed.

In summary, the phenomenon of oil gelling is a complex process that is influenced by temperature, composition, and the presence of additives. While the term "gel" is not typically used, the process of waxing or gelling begins at temperatures below 32°F (0°C) for many types of oil, leading to an increase in viscosity and a change in the physical state of the oil. Understanding and managing this process is crucial for ensuring the smooth operation of systems that rely on oil as a fuel or lubricant.

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The #2 fuel oils (both clear diesel fuel and dyed home heating oil) do not freeze but rather "gel" or thicken to a soft wax. This begins to occur when temperatures drop below 32F, when the fuel starts to become "cloudy" (but still flows readily).read more >>