1. What is Viscosity Index?

Viscosity Index (VI) is a dimensionless number that indicates how much the viscosity of an oil changes with temperature. A higher VI means the oil's viscosity changes less with temperature variations.

2. How Does the Calculator Work?

The calculator uses the Viscosity Index formula:

Where:

• \( L \) — Viscosity at 40°C of oil with VI=0 (cSt)
• \( U \) — Viscosity at 40°C of unknown oil (cSt)
• \( H \) — Viscosity at 40°C of oil with VI=100 (cSt)

Explanation: The formula compares the viscosity-temperature relationship of an unknown oil to two reference oils with known viscosity indices.

3. Importance of Viscosity Index

Details: VI is crucial for lubricant selection in applications with wide temperature ranges. Higher VI oils maintain more stable viscosity across temperature variations, providing better lubrication protection.

4. Using the Calculator

Tips: Enter all viscosity values in centistokes (cSt) at 40°C. Ensure L and H values are different (L ≠ H) for valid calculation.

5. Frequently Asked Questions (FAQ)

Q1: What is a good Viscosity Index value?
A: Generally, VI above 95 is considered good, above 110 is very good, and above 130 is excellent for most applications.

Q2: Why is VI important for lubricants?
A: Higher VI oils provide better protection across temperature ranges, reducing wear and improving equipment performance.

Q3: How can I improve VI of an oil?
A: VI can be improved through refining processes or by adding VI improver additives to the base oil.

Q4: What are typical VI values for different oils?
A: Mineral oils: 80-110, Synthetic oils: 120-200, High VI synthetics: up to 400+.

Q5: Does VI affect oil change intervals?
A: Higher VI oils often allow for extended drain intervals due to better stability and performance across temperatures.