Originally Posted By: addyguy
Can someone tell me just HOW much difference their is between different group III's??
Most Group IIIs being used in motor oils are the "conventional" type, hydrocracked from petroleum distillates and having a Viscosity Index (VI) in the 120s.
Group III+ base oils are usually made from slack wax and have less ringed molecules (aromatics and naphthenics), thus having a higher VI (140s).
In addition to a higher VI, Group III+ base oils will have somewhat better oxidative stability, volatility, and low temperature properties.
The degree of benefits from Group IIIs is pretty much a function of the VI, which is a good indicator of the aromatic/naphthenic content and degree of molecular branching. A minimal Group III with a VI of 120 is only VI point above a Group II+, but crosses that magical (and mythical) line between "mineral oil" and "synthetic". A Group III+ with a VI over 140 is a significant improvement and approaches PAO in high temperature stability. Intermediate VIs will have intermediate performance.
Group IIIs from different suppliers with VIs in the 120s are going to be very similar in performance, with additive differences playing a much greater role. Those with higher VIs will be incrementally better, but again the differences can be wiped out by differences in the additive package. A good formulator will be able to bring forth the performance benefits available with higher VI Group IIIs.
SK is the largest supplier of Group IIIs with a 50% global market share. Their Yubase 4 base oil has a VI of 123. They have now introduced higher VI Group IIIs with VIs in the 130s and 140s.
SK's Group III+ base oils are about 20% higher in price than their standard Group III, which amounts to about 20 cents per quart. That is enough of a price difference to cause an oil marketer to resist using GROUP III+ base oils unless they have specific market claim or specification targets that absolutely require a higher level of performance from the base oil. If a marketer openly states that their current product is based on a Group III, then I would expect that marketer to openly and actively promote the fact that they are switching to a Group III+ in order to differentiate the new product, just as they would promote the word "synthetic" when they move from Group IIs to Group IIIs. Of course some marketers may choose to not offer that level of detail, especially if they are more keen on differentiating their Group III line from their Group IV/V line.
For further reading, see:
Yubase
Tom NJ