These additives are used if the viscosity characteristic of an oil at different temperatures needs to be altered. Multigrade oils, with few exceptions, contain polymers to thicken a monograde oil of a lighter grade and give it multigrade properties, i.e. they are able to function better at much lower temperatures whilst retaining their high temperature characteristics. Some authorities stipulate the use of multigrade oils in emergency equipment due to their excellent viscosity/temperature characteristics. This type of additive is also used in some hydraulic oils to adjust the viscosity/temperature characteristics.
Included to protect vulnerable metal surfaces from atmospheric corrosion, especially when machinery is idle or during overhaul.
Also include alkaline materials to neutralise strong acids as they are formed during combustion. This group of materials also provide detergency.