The process that can lead to the formation of a viscous material like tar in engine oil is thermal cracking. Thermal cracking occurs when hydrocarbons in the oil are subjected to high temperatures for extended periods, causing them to break down into smaller molecules. This decomposition process generates heavier, more complex hydrocarbons that contribute to increased viscosity, resulting in the formation of tar-like deposits.
In the context of engine operation, prolonged exposure to high temperatures can lead to thermal cracking of the oil. As the oil heats up, especially in high-performance or poorly cooled engines, the breakdown of lighter hydrocarbon compounds occurs. This leads not only to a decrease in the oil's overall lubricating properties but also to the byproducts that create thick, sticky residues similar to tar.
Understanding thermal cracking is crucial for engine maintenance and oil selection, as it emphasizes the importance of using high-quality oils that can withstand extreme conditions without breaking down, thus preventing sludge and deposit formation.