What does Viscosity Index (VI) measure?

Viscosity Index (VI) is one of the fundamental indicators of the suitability of your lubricant for the application. With modern synthetic base oils and viscosity modifier additives, formulators have more control over the viscosity-temperature relationship than ever.

Here at Lubrication Expert we take a first-principles approach to lubricants and greases; helping industry understand lubrication technology and pushing the limits of what is possible.

[rumial-afghani]

You saved me sir, my car require full synthetic and
I use my oem oil from dealership always and just realize the vi is 120, barely enough to call it synthetic, what a cheap trick.
Thank you, ill binge all your videos to educate myself

[chippyjohn]

When looking at Penrite oils for example, the viscosity ratings in Cst do not match up with the ratings. For instance a 5w oil is about 15cst at 40c, but according to viscosity charts a 5W should be about about 20 Cst at 40c. The same for 10W and 15W, their ratings seem to be lower than what the classification is supposed to be. Can you explain that at all? In their PAO oils the disparity is even higher. They state a 10W oil which is supposed to be circa 25Cst at 40c but their chart states it is about 15Cst at 40c. It seems their oils are thinner than what they are actually labeled. They have 5W oils which have the same viscosity as 10W oils. It seems labeling or product names are irrelevant. How does this compare with what a manufacturer recommends, if they state a 20W-50 but the 20W50 is actually more like a 5W-30 oil.

[foodadimachan]

I am reaching out to seek clarification regarding the measurement of the VI (Viscosity Index) for our application. As we know, the VI is typically assessed on a scale ranging from 0 to 100°C. However, I would like to understand why we are focusing on a range of 40 to 100°C in our VI evaluations.

Could you please provide insights into the reasoning behind this specific temperature range? Additionally, understanding the implications of settling on a VI within this range will be beneficial in determining the most suitable VI for our application.

Thanks in advance

[mohdsufiyanchauhan]

Will it be better if I use 10w50 instead of 20w50 ?

[fahdbanafa]

Is less saturated base oil better to tolerate more capacity of dissolving dirt & byproducts in the engine pathways???

[hasnainbaig]

Amazingly explained..
I have a few questions for you.
1. Can you please provide the relation between viscosity Index and Viscosity Grade? Is there any chart, formula or something

2. Also how can we know the actual viscosity by looking at the viscosity grade like what is the viscosity of 5W20?

3. What minerals/chemicals are employed in making these engine oils which makes them operable on cold and hot conditions simultaneously.

[Charkatak]

What do you think about the following oils: 1) Honda/Acura synthetic blend 5w-20 which has VI of 159, Kinematic Viscosity at 40°C is 47 and at 100°C is 8.5. 2) Pennzoil Platinum full synthetic (5w-20) which has VI of 167, at 40°C is 45.9 and at 100°C is 8.6. Which would be better overall for my vehicle when doing not more than 5k miles OCI and get better gas mileage?

[bruceparr]

I was using some old soviet stuff where cst was quoted at 50 degrees. I used an educated guess.

[robertogomez]

I have a question if you could help my it would be great:
I´m trying to see which low viscosity transmission fluid is better. Option A is Pentosin ATF 1 LV with a VI of 168 a Kinematic viscosity at 100ºC of 5.6 mm2/S and 25.3 mm2/s at 40ºC. Option B would be Motorcraft Mercon LV with a VI of 155, a cst @100ºC of 6.0 and a cst @40ºC of 29.6.
From what I could learned from your video I would say Pentosin because it´s VI is higher, but they seem to be very similar, am I right?, can they be interchangeable?
Thanks again for the information.

[bdykes]

Please label your graph axies with titles (and units if applicable.)