The pour point of a fuel or oil is the lowest temperature at which it will pour when cooled under defined conditions. In general, the pour point is indicative of the amount of wax in an oil. At low temperatures, the wax tends to separate, trapping a substantial amount of oil, inhibiting oil flow and hindering lubrication.
Although most of the wax is removed during base oil refining, some wax is desirable for achieving the right viscosity. So pour point depressants are added, allowing mineral oils to function efficiently at low temperatures, while keeping the viscosity benefits of the wax at higher temperatures.
Good additives can lower the pour point by as much as 40°C. These are commonly used in applications requiring mineral oil, usually below 0°C. By altering the wax crystal size, they inhibit lateral crystal growth and keep the bulk oil in a liquid state.
Pour point depressants are used in most lubricant types, including crankcase engine oils, automatic and power transmission fluids, automotive gear oils, tractor fluids, hydraulic fluids, and circulating oils.