Viscostatic lubricating oils

In order to allow the lubricant to work at low temperatures, the viscosity of the base oil has to be kept quite low. Also, the polymer molecules are coiled up, or even aggregated into a colloid, so they do not contribute to, or cause, an overly high viscosity. Then, as the temperature is increased, so the viscosity of the base oil will drop and its ability effectively to lubricate the bearings will decrease. 

Other mechanisms, such as using a polymer which separates into a colloid suspension at very low temperatures, but dissolves to exert an added viscosity at high temperatures, formation of hydrogen bonds, or creation of ionic interactions, are used to maintain polymer—polymer interactions and thereby sustain the effectiveness of the lubricant. 

a properly formulated lubricant shows the desired properties of flow and energy absorption at the shear rates for which it has been designed. However, at higher shear rates, the polymer molecules do not have time to undergo the required movements, and the viscous fluid lubricating film behaves like a rubber membrane. 

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