what is the difference between SUS and cSt in viscosity oil analysis?

[1 FMF]

SUS = Saybolt Universal Seconds. A measure of lubricating oil viscosity in the oil industry. The measuring apparatus is filled with specific quantity of oil or other fluid and its flow time through standatized offrice is measured in Seconds cSt = centistokes, The worldwide unit of kinematic viscosity. I got those definitions from the glossary page on the board. In past oil analysis, and on spec sheets for oil, I see oil viscosities at 40C and 100C in cST, but I also see viscosities in SUS at 210F, and I don't know what temp for SUS corresponds to 40C cSt. What are the differences between these two measurements? Is one better than the other, or is it just a scale thing, like what inches is to centimeters? Or is the viscosity measurement fundamentally different for cSt than it is for SUS? For SUS it sounds like all that is done is the fluid is timed to see how long it takes to flow in a tube. Can someone comment more specifically how that is done?

 

[Al]

They are both known as kinematic viscosities (a measure of restrictive flow). Essentially one is ISO (Internal standards Organization) cSt is measured at 40 C and 100 C. SUS is the older "English" Measurement and is measured at 100 F and 210 F. cSt. is probably more common. An approximate equation is V=(.22S-180/S) where V is in cSt and S is in SUS.