If you spent some time on BITOG, you must have got the idea that there is no such thing as the best oil or whether thin is always better than thick or vice versa. For example, we know that thicker oil usually tends to provide better wear protection.
One question I always wondered about was the relative base-oil quality of the thinner and thicker base stocks within the same base-stock family. In other words, is a thinner Shell Pearl GTL base stock of higher or lower quality than a thicker Shell Pearl GTL base stock?
My base-oil-quality index (BOQI ~ 1/CCS/NOACK), which has turned out to be extremely robust and useful, has long predicted that thinner base stocks are superior to thicker base stocks in base-oil quality. 0W-20 scores higher than 5W-30, which in turn scores higher than 10W-30, which in turn scores higher than 15W-40 in BOQI. Base-oil quality (BOQI) primarily relates to an oil's oxidation stability, which determines the OCI length and engine cleaning.
However, without actual data, we wouldn't know if this is an artifact of BOQI or thinner base oils indeed have higher base-oil quality (less oxidation). I've finally found a scientific study, which clearly demonstrated that thinner base oils indeed have more oxidation stability and leave less deposits and allow longer OCI's than thicker base oils.
Effects of hydroprocessing on structure and properties of base oils using NMR (PDF link)
In stark contrast to almost everyone's intuition on BITOG, within the same base-stock family, lower the NOACK (less the evaporation) is, the more the deposits the oil leaves on the engine and less the OCI length are! So, low NOACK by itself can be a bad thing!
If you are concerned about the base-oil quality, low NOACK by itself is not the answer and it can ironically work both for the base-oil quality and against base-oil quality. If you consider the NOACK and CCS together as in the BOQI, then you will get a more definite answer.
As an example, Pennzoil Platinum 0W-20 (higher NOACK) would result in better engine cleaning and allow a longer OCI than Pennzoil Platinum 5W-20 (lower NOACK) because they are made from the same base-stock family (Shell Pearl GTL) but the the 0W-20 has a thinner base oil, which results in less oxidation and deposits.
One question I always wondered about was the relative base-oil quality of the thinner and thicker base stocks within the same base-stock family. In other words, is a thinner Shell Pearl GTL base stock of higher or lower quality than a thicker Shell Pearl GTL base stock?
My base-oil-quality index (BOQI ~ 1/CCS/NOACK), which has turned out to be extremely robust and useful, has long predicted that thinner base stocks are superior to thicker base stocks in base-oil quality. 0W-20 scores higher than 5W-30, which in turn scores higher than 10W-30, which in turn scores higher than 15W-40 in BOQI. Base-oil quality (BOQI) primarily relates to an oil's oxidation stability, which determines the OCI length and engine cleaning.
However, without actual data, we wouldn't know if this is an artifact of BOQI or thinner base oils indeed have higher base-oil quality (less oxidation). I've finally found a scientific study, which clearly demonstrated that thinner base oils indeed have more oxidation stability and leave less deposits and allow longer OCI's than thicker base oils.
Effects of hydroprocessing on structure and properties of base oils using NMR (PDF link)
In stark contrast to almost everyone's intuition on BITOG, within the same base-stock family, lower the NOACK (less the evaporation) is, the more the deposits the oil leaves on the engine and less the OCI length are! So, low NOACK by itself can be a bad thing!
If you are concerned about the base-oil quality, low NOACK by itself is not the answer and it can ironically work both for the base-oil quality and against base-oil quality. If you consider the NOACK and CCS together as in the BOQI, then you will get a more definite answer.
As an example, Pennzoil Platinum 0W-20 (higher NOACK) would result in better engine cleaning and allow a longer OCI than Pennzoil Platinum 5W-20 (lower NOACK) because they are made from the same base-stock family (Shell Pearl GTL) but the the 0W-20 has a thinner base oil, which results in less oxidation and deposits.