Multigrade oils

The function of viscosity additives is to improve the viscosity index so as to obtain multigrade oils. The problem is to use materials that, by only slightly increasing the low temperature viscosity, are capable of counterbalancing the decrease in viscosity when the temperature increases. 

Fig. 13. Thickening of lOW base stock to multigraded oil with polymer additives. A, high mol wt poly(alkyl methacrylate) B, low mol wt poly(aLkyl...

Multigrade batch processing, 20 703 Multigrade oils, 15 225 Multigrain model, of polymer growth, 26 528... 

Multigrade motor oils do not behave as Newtonian oils, and the improved viscosity-temperature characteristics of multigrade oils enables, for example, an oil to be formulated to have mixed characteristics (ASTM D-2602, ASTM D-3829). 

However, multigrade oils do not behave as Newtonian fluids and this is primarily due to the presence of polymeric viscosity index improvers. The result is that the viscosity of multigrade oils is generally higher at -18°C (0°F) than is predicted by extrapolation from 38°C (100°F) and 99°C (210°F) data, the extent of the deviation varying with the type and amount of viscosity index improver used. To overcome this, the SAE classification is based on a measured viscosity at -18°C (0°F) using a laboratory test apparatus known as a cold cranking simulator (ASTM D-2602). 

Lane, G., Roberts, D.C. and Tims, J.M. (1977) Measurement of the viscosity of multigrade oils in a running engine. SAE Trans. 86 Paper 770379. 

CMls shall meet all of the requirements of SAE J300. Viscosity grades are limited to SAE OW, 5 W and lOW multigrade oils. 

As mentioned earlier, oil additives play a very important role (such as that of VI improvers for multigrade oils). Antiwear agents such as zinc dialkyldithiophosphate (ZDDP) are shown in Figure 7.4. These compounds feature zinc bound to the anion of dithiophosphoric acid. ZDDPs are soluble in mineral and synthetic oils. This antiwear additive is present in most commercial oils. Its quantity is limited in order to minimize interactions with catalytic converters. ZDDP also contains calcium and protects engine oil from oxidative breakdown and sludge formation. Concentrations in fluids are around 1-2% [4], These compounds are manufactured by treating phosphorus penta-sulflde with an alcohol. Zinc oxide is then reacted with the resulting dithiophosphate ... 

Bartz, W. J. (1999). Influence of viscosity index improver, molecular weight, and base oil on thickening tendency, shear stability, and evaporation losses of multigrade oils. Lub. Sci. 12(1), 215-237. 

Viscosity index improvers. Help keep the oil from thinning as fast with temperature rise, thus allowing a wider range of serviceability. These additives are long-chain polymers, most widely used in motor oils to create multigrade oils. 

Obviously lOW and 20W oils of any base are satisfactory for normal winter service. Zero Viscosity Index oils are not shown in the tabulation, because such oils are not marketed. So called multigrade oils are being marketed which meet the requirements of several or all SAE grades. 

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