Hydraulic oils used for low temperature applications should have a low?

Hydraulic oils used in low-temperature applications need to have a low pour point. The pour point is the lowest temperature at which a liquid remains pourable under specified test conditions. Oils with a low pour point ensure that they can flow and function properly even in very cold environments. This is essential for maintaining effective hydraulic system operation, as it allows the oil to circulate freely without risk of gelling or becoming too viscous, thereby facilitating the proper functioning of hydraulic machinery and equipment.

In contrast, a high viscosity index indicates that the oil's viscosity changes significantly with temperature, which isn't beneficial for low-temperature environments where consistent performance is crucial. Vapor pressure is more concerned with the oil's tendency to evaporate, which is less critical than ensuring proper flow at low temperatures. The oxidation rate relates to the oil's stability over time, particularly under heat, but it does not directly impact low-temperature fluidity in the same way as the pour point.