How is the Shear Stability of the Shell Tellus S2 VX 68? In comparison with other brands?

Shell reports that Shear Stability of Tellus S2 VX 68 is a 14% viscosity loss at 100 °C when tested via the CEC L‑45‑A‑99 method. That’s a strong result—Group II fluids typically target <20–25% loss, so 14% is well below this threshold.
 
What it means and how it compares
Shear stability indicates how well the oil maintains its viscosity under mechanical stress (like high-pressure pump operation). A lower percentage means the oil retains more viscosity, helping maintain proper lubrication film and system performance over time.
Shell Tellus S2 VX 68 (Group II) — 14% loss at 100 °C
ISO‑HM (Group I) oils (e.g., legacy HM fluids) often show 20–30% viscosity loss under the same conditions, making them more prone to thinning over time 
 
Why that matters
Viscosity retention: By shedding only about 14% viscosity under extreme stress, Tellus S2 VX remains closer to its nominal ISO VG 68, preserving protection of seals, hydraulic clearances, and wear surfaces.
Extended service life: With high shear stability, there's less viscosity drift, meaning longer maintenance intervals and safer performance margins, especially in demanding or precision hydraulic equipment.
Temperature resilience: Shell’s switch to a high-grade Group II base and robust viscosity modifiers enhances both shear and thermal stability compared to older HM oils.

Overall, Tellus S2 VX 68 is right in the upper tier of shear-stable hydraulic oils, outperforming standard HM oils and matching most premium Group II competitors.