How to read a PAO base-oil TDS: what each ASTM method actually measures

A technical data sheet is a contract of measurement, not a list of adjectives. When two suppliers both quote "KV40 = 4.0 cSt", the figures are comparable only if both were produced by the same capillary procedure at the same temperature. That is why every parameter on our PAO sheets carries its method: kinematic viscosity at 40 °C and 100 °C by ASTM D445, the pair from which the viscosity index is then calculated according to ASTM D2270.

Pour point (ASTM D97) is frequently over-read. It records the lowest temperature at which the fluid still flows under a specific test geometry; it says nothing about the torque a pump needs at that temperature. For cold-start behaviour we therefore also quote low-temperature Brookfield viscosity (ASTM D2983), the quantity that correlates with cranking and pumping performance in real equipment.

Volatility is where synthetic and mineral base stocks diverge most clearly. The Noack test (ASTM D5800) holds the fluid at 250 °C for one hour and reports the mass lost; lower Noack loss means less top-up, slower viscosity growth and fewer deposits in hot zones. PAO grades typically sit far below Group I/II mineral stocks of the same viscosity class.

Density at 15 °C (ASTM D1298 or D4052) closes the loop for logistics: it converts delivered volume into mass for customs declaration and for batch reconciliation against the certificate of analysis. Flash point by Cleveland open cup (ASTM D92) completes the safety picture for storage and transport classification.

When comparing suppliers, ask for the method list first. A sheet that reports values without methods cannot be audited; a sheet that reports methods can be re-tested in your own or a third-party laboratory — which is exactly what a qualification process needs.