Denver Full Service Machine Shop

All About That Base
Base oils are rated according to their “Viscosity Index” (VI) or pour point, how many “saturates” (paraffin and naphthenes) they contain, sulfur content, volatility, flash point, oxidation stability and other factors. Petroleum engineers have developed test procedures and a rating system for grading various base stocks.
• Group I oils are the easiest to refine and least expensive lubricants. They also contain lower levels of saturates (less than 90), higher levels of sulfur (over 500 ppm) and usually have a viscosity index rating of less than 100. Group I mineral oils have long been used in straight weight and multi-viscosity everyday motor oils, and are often blended with Group II or III oils in some multi-viscosity oils. But Group I base oils are generally not used in racing oils.
• Group II base oils are higher quality lubricants that are commonly used in today’s multi-viscosity oils. They contain a higher percentage of saturates (greater than 90), lower levels of sulfur (less than 500 ppm), and have a viscosity index rating over 100.
• Group III base oils have a viscosity index rating usually over 120, and include many synthetic oils.
• Group IV base oils are pure PAO synthetics and are the highest quality generally used in automotive applications.
Which group a base oil ends up in depends on how it was refined or made, and how it performs. Mineral base oils are refined from crude oil (paraffinic, naphthenic and aromatic) while synthetic oils undergo additional refining and may be made from crude oil or natural gas. Synthetic oils fall into several subcategories: PAOs (polyalphaoefin), diesters, polyol esters and PAGs (polyalkylene glycols).
This is a lot of chemistry you really don’t need to know to choose a racing oil. But it’s helpful to understand what some of these terms mean and how marketing people tend to misuse them in promoting various high performance lubricants.
The general consensus is that synthetic oil is better than conventional mineral oil. Most synthetic oils do have inherent advantages over conventional oils because synthetic oils undergo additional refining, distillation and purification that results in a very high quality and consistent base stock. Synthetic oils generally pour more easily at lower temperatures, resist oxidation better at higher temperatures, stay cleaner longer (extended drain intervals) and superior lubrication and wear protection. One oil supplier says the molecules in synthetic oils are more consistent in size. This allows a synthetic oil to provide a higher film strength. Translated, this means although a synthetic oil is often thinner than a conventional mineral oil, it clings better to bearing surfaces under load.
Synthetic oils also have lower volatility, which reduces evaporation losses when the oil is hot. Synthetic oil is also more sheer stable, which means its viscosity characteristics are more predictable and consistent, and undergo less change over time than a conventional mineral oil. Some synthetic oils also provide better air release, reducing the risk of aeration and bubbles being trapped in the oil when it is being whipped into foam by a spinning crankshaft.
High-quality conventional mineral oils can perform well in many racing applications with the right additive package, but for the most demanding applications many oil experts say a full synthetic will usually provide the best protection and performance.
Oil is relatively cheap, even the most expensive full synthetic racing oils when you compare the cost of the oil to all of the machine work and parts that have gone into a high performance engine. Why scrimp on oil quality and risk an engine failure if a premium quality racing oil can provide extra protection?