This topic is being discussed in the PCMO thread about the
base-oil viscosity, which I called HTFSV (high-temperature, full-shear viscosity):
HTFSV: high-temperature, full-shear viscosity
The very first base-oil viscosity (HTFSV) table I calculated doesn't have the density correction factor and VII adjustable parameter optimized. Refer to the later tables in the thread for more accurate values of the base-oil viscosity.
Chevron has a very nice brochure about their Group II oils. It's very informative indeed. One of its pages is dedicated to the base-oil viscosity. They explicitly and very confidently state that:
- "Heavier base-oil viscosity improves performance"
- "In HDMO (HDEO), wear decreases as (base-oil) viscosity increases (from 5W to 10W to 15W)"
- "Commercial proof: Proof that a heavier base-oil viscosity is critical to wear control."
Therefore, they go as far as saying that they have
proved the base-oil viscosity to be critical to wear control.
They did their tests on a mini traction meter (MTM) using both experimental oils (5W-30, 10W-30, and 15W-30) and commercially available oils (5W-40 and 15W-40).
The results were such that the 5W-30 produced more wear than the 10W-30, which in turn produced more wear than the 15W-30. The CJ-4 5W-40 produced more wear than the CJ-4 15W-40. The results are the same for both fresh and sooted oil.
Here is the full Chevron brochure:
Chevron Group II base oils: optimise automotive engine oils