The question often arises; “Why spend the extra money?” Why buy a synthetic PAO, Diester, PAG or POE rather than a severely hydro-treated “synthetic” petroleum? When one compares synthetic PAO (Polyalphaolefin, API Group IV) to synthetic petroleum (API Group III), one can expect to see the same clear color, similar specific gravity, and similar VI (viscosity index). VI is a measure of how an oil will thin out under high temperature. It is one of the properties used to distinguish synthetic fluids from mineral based fluids and is very important to OEM’s who manufacture hot and cold running equipment.
So what are the benefits that justify the added expense of synthetic PAO? When comparing physical properties from a Technical Data Sheet or MSDS, we should recognize a major difference in pour point. ASTM test method D97, measures the lowest temperature at which a given fluid will flow. A typical PAO will have a pour point of -60°F while a typical Group III will pour down to about -35°F. So, if you are operating equipment outdoors in Northern winter climates, you will see that justification very quickly. However, what if your equipment is safe and warm within your shop or factory? How do I justify synthetics?