Base oil cSt relation to Gravity API ASTM D4052

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Hi, i have observe a very interesting relation between the Gravity API weight, pound per gallon with actual base fluid cSt. It seem that the thicker the oil, the heavier is the Gravity API weight and Flash point.

From the sample below, it seem that the Supergard 5w30 & 10w40 is spike with VII to increase it's cSt@100'c to meet 30wt and 40wt.

What do you guys think about this relationship between base fluid cSt and API Gravity theory? does it make sense?

Sample data sheet - Citgo
 
Yes, generally speaking, the specific gravity of the same API category base oils will climb as the viscosity increases.

However, specific gravity tends to fall as the VI index increases.

So a 4 cSt PAO is lower specific gravity than a 4 cSt Grp III, and the 4 cSt Grp III is lower than a 4 cSt Grp II, etc.

Reference this comparison of 4 cSt base oils at the Chevron website:

Chevron 4 cSt Base Oils Comparison
 
API gravity is older than me, it was used to denote difference or "quality, VI, base oil type" years ago.

good "oils" were API 28 low VI bad oils were 35 or whatever not used anymore much other than weight truck loads of oil and to convert the lbs loaded into gallons for billing purposes.
bruce
 
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