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Originally Posted by RubHer Yellow Ducky
Conventional motor oil is a batch of short-chain and long-chair carbon and hydrogen atoms. In extreme heat, the short chains can evaporate and these unstable molecules oxidize and break down. In addition, contaminants and reactive and/or unstable hydrocarbons can sneak through the refining process.
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Thanks for the article RYD. I've read a lot about synthetic vs regular oil, and next to their low-temperature pour point, this part of the explanation is what convinced me to switch to Mobil1 several years ago.
As I understand it, conventional oil meets industry specs based on the average characteristics of its oil molecules, such as size, density, viscosity and oxidation rate, at defined temperatures (with allowable improvements through an additive package). Smaller molecules lower average viscosity in cold temps and larger molecules maintain viscosity at higher temps. But as conventional oil stays in your engine, the smaller less complex molecules evaporate and oxidize first. Thus, the oil's average molecular weight rises due to the attrition of lightweight molecules. It becomes more viscous in cold temps and more corrosive to internal components as acids build up. (The additive package counteracts this corrosion but depletes over time)
To solve this problem, Group IV synthetics were created with PAO molecules of uniform size and weight. To maintain desired viscosity at various temperatures, the molecules were engineered to change shape as temperature varies. At low temperatures, the PAOs coil up (getting physically shorter) for lower viscosity. At high temps, they unwind (physically lengthen) to retain viscosity.
Group IV molecules can still break down under heat and shearing stress. But since there are no lightweight molecules to evaporate and oxidize, their average molecular weight is more stable over time. The coiling and uncoiling maintains the oil's original viscosity parameters and cold weather performance lasts much longer than conventional oil. Due to lower oxidation rates, its acidity also rises more slowly and is countered by the additive package.
To me this means low-temperature pour points, better cold-weather starts and performance, and either better protection at the recommended service interval or at least the same protection over extended intervals.