Originally Posted By: CATERHAM
Originally Posted By: Gokhan
Originally Posted By: CATERHAM
The Toyota 0W-20 has a higher KV100 undoubtedly due to it's higher VII content.
Ah, actually I don't agree with that at all.
You can't simply dump a ton of viscosity-index improvers (VIIs) into an oil in order to obtain an ultra-high viscosity index (VI). There is a limit to the amount of VIIs you can add to the oil, and the oil blenders know that limit very well.
If you add too much VIIs, since they shear temporarily at high shear (high shear is fast and close moving parts; VIIs make the oil a non-Newtonian fluid, which has a lower viscosity at high shear than at low shear), they would result in an HTHS (high-temperature, high-shear) viscosity that is too low, which is not allowed by the SAE specification that limits it to a minimum of 2.6 cP for xW-20.
Also, VIIs are polymers (plastics) and too much of them would ruin an engine with sludge.
Sustina claims that the high VI of their oil is due to the W BASE of Nippon Oil they use, which is the new breed of ultra-high-VI Group III+ base oil. YUBASE of Korea, the largest manufacturer of Group III in the world, also makes the new breed of ultra-high-VI Group III+ base oil.
So, in most likeliness, the high VI of the Toyota 0W-20 is due to the special base oil they use. Is it Group III+, IV, V, or a mixture of them? I don't know and no one knows, except ExxonMobil. The best guess is that it's a mixture of YUBASE or Nippon Group III+ along with ExxonMobil's excellent Group IV and V truly synthetic base oils.
It still has a lot of VIIs.
Using the Sustina example, the VI of the GP III+ base oil is 145 but the finished oil has a VI of 229.
Optimistcally I'd guess that the Toyota 0W-20 base oil has a VI no higher than 130. So whether you consider the amount of VIIs necessary to bump the finished oil up to 216 as a lot or not, it's certainly a lot more than what is contained in a dino 5W-20.
It's much more complicated. You can't tell how much VIIs are in an oil just by looking at the VI. It's a complicated science, which has evolved a lot.
Lubrizol has a VII blending-calculator page
here. I used the ExxonMobil SpectraSyn 4 PAO basestock (KV40 19, KV100 4.3, VI 126) and SpectraSyn 6 PAO basestock (KV40 31, KV100 5.8, VI 138) and chose ISO-32 (roughly SAE xW-20). It popped out VII concentrations between 5.0 - 9.2% (depending on the VII type) to generate a ultra high VI of 216, which are pretty low concentrations for VIIs.
We don't know what the base oils used in Toyota 0W-20 are. They could be any combination of Group III, III+, IV, and V.
Amount of VIIs also affect the HTHS viscosity a lot (due to temporary shear of VIIs at high shear rates). Therefore, there are even more factors in choosing the right concentration of VIIs.
More references:
ExxonMobil Group IV/V base oils blending guide
YUBASE Group III base oils