Multiviscosity motor oils

The purpose of a multiviscosity motor oil is to offer good engine protection over the operating range of the engine from a cold start to the normal operation temperature. Addition of a low Tg polymer allows for a wider range where viscosity is approximately constant. 

A polymer may be internally plasticized by random copolymerization with a monomer whose homopolymer is very soft (has a low Tg, see Chapter 6). There are obviously never any permanence problems when this is done. The composition of the copolymer can be adjusted to give the desired properties at a particular temperature. Above this temperature, the copolymer will be softer than intended and below this temperature, it wUl be harder. With external plasticizers, the same sort of temperature compensation as in the multiviscosity motor oils is obtained, giving materials that maintain the desired flexibility over a broader temperature range. 

MV EG MVMA different viscosities at 100°C. Fluids with very high natural viscosity indexes, such as some synthetic fluids, are also classified as multiviscosity. Motor Vehicle Emission Group (Europe). Motor Vehicle Manufacturers Association (U.S. passengers cars). A North American OEM association. As part of ILSAC, it participates in promoting the ILSAC engine oil standards. 

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