Furthermore, the oil should not thin due to shear, nor thicken due to oxidation or soot accumulation, and it must combat chemical contact with tens of thousands of miles of acidic blowby. To best protect engines under these severe conditions, it is tempting to simply add more and more anti-wear additives. However, prevention has been found to be the better cure. For example, controlling piston skirt varnish and deposits in the ring lands behind the rings effectively prevents cylinder wear. And keeping soot dispersed in the oil rather than allowing it to settle or agglomerate prevents sludge, valvetrain wear, and oil thickening.
Synthetics are a special case.
Because the base oil characteristics, the synthetic fluid needs far less VII, so synthetic oils are inherently shear stable. The base oil is highly resistant to oxidation, although mineral oils contain anti-oxidant additives that provide adequate protection. Synthetic base oils, however, are not good solvents, so additional dispersants must be added to provide adequate cleanliness performance. And since the price of additives and the price of the synthetic base oil are similar, it does not cost substantially more to use a higher additive treat rate in a synthetic oil formulation, making it more difficult to make accurate assumptions about their performance without actual testing. Two areas that do make synthetics superior are the ultra low temperature performance, when it will flow at temperatures you wouldn't drive in, and in volatility, meaning it will not vaporize at engine operating temperatures.