Some of the physical or chemical properties of lubricating oils can be influenced with additional molecules. Some of the properties have to be provided with the base oil, as they cannot be modified afterwards. Examples for non-influenceable properties are: volatility, sulfate content, content of ash builders, air release characteristics, and disruptive strength. Viscosity modifier (VM)
A good lubricant provides excellent flow ability at cold ambient temperatures as well as under hot circumstances. To be able to show this feature, the oil needs viscosity modifiers and, in fact, to increase the viscosity index value. With these polymers mineral oils can become multi-grade oils and the VI of synthetic oils can be improved or at least maintained. VMs consist of very large, thread-like hydrocarbons which are spatially small at cold temperatures, but extend and widen when it gets warmer. They can be sheared and destroyed because of their size and, therefore, attention to the engine system must be paid if VMs are suitable for this precise application.
Pour point depressant (PPD)
At very cold temperatures mineral oil tends to crystallize and harden. The paraffin inside the oil is discharged and interacts, the phase of the oil is negatively influenced. Pour point depressants cannot prevent the crystallization, but they inhibit the growing and the interconnection of the wax crystals. The oil stays liquid and can be used till -49 °C (-56 °F) on an average with specific fully synthetic blends.
Seal swell agents (SSA)
Specific synthetic hydrocarbons (PAOs) can dry out the seals inside an engine and they would shrink and become brittle. The sealing effect is not guaranteed anymore and while operating the engine could get severely damaged. To save the elastomers from drying out, SSAs protect specifically these kind of plastics and help preserving the integrity of the seals by swelling the sealing device.