- Effect of temperature:
The temperature and the amount of movement of the molecules are considered equivalent. When the temperature of any substance increases (especially liquids and gases), its molecules become more mobile and its cohesion decreases, as do the actions of intermolecular forces. Viscosity varies with temperature, increasing with a decrease in temperature and decreasing with an increase in temperature.
- Effect of shear rate
Not all fluids respond the same to changes in shear rate. Due to their nature, most fluids do not vary their viscosity when this factor changes. These are called Newtonian fluids. In these, the degree of displacement of the liquid layers is proportional to the force applied.
- Effect of foreign substances:
During use, the lubricant is exposed to foreign substances that, sooner or later, will affect it, modifying its characteristics.
The viscosity of an oil can decrease due to:
- Low-quality base
- – Dissolution by another substance
- – Accumulation of contaminants
- – Oxidation
The above factors can combine their actions, so that they may even cancel each other out. That is, a lubricant can lose viscosity due to a low-quality base and recover it due to the accumulation of dirt. In any case, this implies a degradation of the lubricant, with the loss of viscosity being even more concerning than its increase.
