Originally Posted By: Tom NJ
The coking test used in the reference link combines
thermal stress (540F), oxidative stress (air flow over oil film), hydrolytic stress (water saturated air), volatility (thin film at high temperature), and solvency (oil flowing over residues). Solvency plays a major role in coking and often reverses the correlation of coking to other high temperature properties. A polar oil with good solvency will dissolve or disperse degradation by-products before they can polymerize into insoluble carboneous deposits.
The coking test at 540°F seems to be relevant for upper ring carbon formation. The
Redline Motor Oil Information Sheet suggests that the upper ring area can see temperatures in the range of 600°F.
Originally Posted By: Tom NJ
In a motor oil, all else being equal,
higher groups would give longer life and less oil thickening than Group I. In theory they would not be as clean as Group I, but in reality the additives are adjusted to correct this deficiency. But no, they
would not give less coking than Group I based oils unless dosed up with esters or high detergent levels.
Aren't PAO oils normally dosed up with POE esters for seal conditioning anyway?
Would a PAO-based CJ-4 HDEO have the esters and detergents that would provide the coking resistance of a Group I oil?