Which of the following is not considered a necessary property for hydraulic oil in hydraulic systems?

In hydraulic systems, the properties of hydraulic oil play a crucial role in ensuring optimal performance and longevity of the equipment. Viscosity is essential as it affects the oil's ability to flow and transmit power; it is the measure of a fluid's resistance to deformation. Thermal stability is critical as it ensures the oil can withstand high temperatures without breaking down or losing its performance properties. Corrosion resistance is important to protect the metal components from rust and degradation caused by moisture and contaminants in the system.

While shock resistance might seem like an important characteristic, it is not a standard requirement for hydraulic oils. Hydraulic systems are designed to manage pressure and flow, and shocks are generally absorbed by the hydraulic components or through the design of the system itself rather than relying on the oil's properties. Therefore, shock resistance does not fall within the necessary properties typically evaluated for hydraulic oil in hydraulic systems.