Which of the following is NOT a common characteristic of hydraulic oils?

Hydraulic oils are designed to perform under various conditions, and several key characteristics define their effectiveness. One of those traits is their non-flammable nature, which enhances safety during operation. Good lubrication properties are also essential because they help reduce friction between moving parts, which extends equipment life and improves efficiency. Additionally, a stable performance over varying temperatures is crucial, as it ensures that the hydraulic system operates effectively in different environmental conditions.

When it comes to water solubility, hydraulic oils typically are not water-soluble. Instead, they are formulated to be resistant to mixing with water, ensuring that they maintain their performance attributes in the presence of water, which can be detrimental to many hydraulic systems. Thus, acknowledging this property helps clarify that water solubility is not a common characteristic of hydraulic oils.