guys,
What is the correct viscosity index range of mono grade oils?95-120??
and for multi garded oils >120??
Am i right??
Original Post
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It depends on the type of base oil used as well ie is it PAO, diester, mineral etc...
NOn VII oils will be close to the original VI of the base oil
GPI-90-95
GPII-110-120
etc
GPI-90-95
GPII-110-120
etc
Multi grade with VII depending 140-170 or so
The official API specification ranges are 80-119 for both Grp I & II, though modern Grp I should run around 95 and Grp II around 110. Grp III will be 120+, PAO around 140 and up.
Of course, a pure PAO has such miserable solvency that it won't hold additives adequately, so it will have 10 - 20% cosolvent. If the cosolvent is a diester, that will drop the VI. Phthalates won't hurt VI as much & trimellitates are right in the same range as PAO's, but both of those are more costly & less available, plus phthalates are becoming a boogeyman. There are still more exotic cosolvents, but they are of limited availability rght now.
So, once you've dropped the VI by adding diester, most blenders add some VI improver to boost it back up to the 140 range.
I'm not sure why; except for mobile equipment or other exterior applications, VI isn't that critical for industrial applications, which tend to be isothermal. I think it's just become part of the synthetic cachet. For industrials, VI is a bit lot octane for auto fuel, people tend to assume that higher is automatically better, when often it's just more expensive. There are some applications where low VI more desirable, like transformer oils
Of course, a pure PAO has such miserable solvency that it won't hold additives adequately, so it will have 10 - 20% cosolvent. If the cosolvent is a diester, that will drop the VI. Phthalates won't hurt VI as much & trimellitates are right in the same range as PAO's, but both of those are more costly & less available, plus phthalates are becoming a boogeyman. There are still more exotic cosolvents, but they are of limited availability rght now.
So, once you've dropped the VI by adding diester, most blenders add some VI improver to boost it back up to the 140 range.
I'm not sure why; except for mobile equipment or other exterior applications, VI isn't that critical for industrial applications, which tend to be isothermal. I think it's just become part of the synthetic cachet. For industrials, VI is a bit lot octane for auto fuel, people tend to assume that higher is automatically better, when often it's just more expensive. There are some applications where low VI more desirable, like transformer oils
