Originally Posted by Gokhan
Originally Posted by painfx
Originally Posted by Gokhan
The fuel-economy improvement will probably result in the SP oils having a higher VII content and a higher viscosity index (VI) than the SN/SN PLUS oils.
Would that affect the timing chain wear?
Of course, wear and fuel economy are a compromise.
They need to lower the base-oil viscosity (BOV) in order to increase the viscosity index (VI) by adding more VII, which then improves the fuel economy. This is because when you increase the VII content and VI, the finished oil runs thinner in a wider temperature range and a wider temporary-shear range. The former is obvious from the definition of VI, and the latter is because when there is more VII, the base oil is thinner, and since the oil viscosity approaches the base-oil viscosity at very high shear rates beyond that of the HTHS measurement, it will be thinner at these higher shear rates.
ExxonMobil recently developed new base stocks to do specifically that and wrote an article on improving the fuel economy in SP/GF-6 by lowering the BOV and increasing the VII content.
If you watch the video, you will see that they advocate increasing the VII (VM) content from 4.1% to 7% by lowering the BOV:
Decreasing BOV and increasing VII to improve fuel efficiency for 5W+ engine oils -- ExxonMobil
However, when you lower the base-oil viscosity (BOV), valvetrain and timing-chain wear increases. To combat that problem, they have better AW/EP/FM additives in SP/GF-6 add packs. Better dispersants in SP/GF-6 add packs also help reduce abrasive particles aggregating and causing timing-chain wear. Likewise you need better detergents and more antioxidants to negate the increased amount of deposit formation by the higher VII content.
I am asking because they are stating GF-6 will help reduce wear on timing chains. So that is confusing...