Improving the viscosity index (VI) of oil means enhancing its ability to maintain a stable viscosity over a wide temperature range—less thinning at high temps, and less thickening at low temps. This is critical for performance in engines, hydraulics, gearboxes, and more.
🔧 How to Improve Oil Viscosity Index
1. Add a Viscosity Index Improver (VII)
The most common and effective method.
| Type of VII | Description |
|---|---|
| Olefin Copolymers (OCP) | Common in engine oils; good shear stability |
| Hydrogenated Styrene-Diene Copolymers | High-performance VIIs (used in synthetic oils) |
| Polymethacrylates (PMA) | Used in hydraulic fluids and gear oils |
| Styrene-Isoprene Copolymers (SIS/SIBS) | Very high VI and oxidation stability |
📌 Typical treat rate: 1% – 10% (depends on base oil and target VI)
2. Use High-Quality Base Oils
Higher base oil groups have naturally better VIs.
| Base Oil Group | Viscosity Index (Typical) |
|---|---|
| Group I | 80–100 |
| Group II | 90–115 |
| Group III | 120–140 |
| Group IV (PAO) | >140 |
| Group V | Variable |
💡 Switching from Group I to Group III/IV will significantly improve VI without as much dependence on VIIs.
3. Minimize Shear Loss of Additives
Use shear-stable VIIs to maintain VI over time (especially in engines or high-shear hydraulic systems). Poor-quality VIIs can degrade and reduce effective VI.
4. Formulate with Synthetic Esters (Group V)
Synthetic esters have very high natural VI and provide:
- Excellent low-temperature flow
- High-temp film strength
- Biodegradability (in eco fluids)
5. Optimize Blending Strategy
Blend multiple base stocks (e.g., small % PAO into Group II) to increase VI cost-effectively.
🧪 Example: Improving a Hydraulic Oil (ISO VG 46) from VI 95 to VI 140
- Start with Group II base oil (~VI 95)
- Add ~4–6% PMA-type VII
- Resulting oil reaches VI ~135–140
⚠️ Notes
- Adding too much VII can reduce oxidation stability and shear resistance
- Always test in high-temp and long-term shear simulations (ASTM D5275, D6278)
- Base oil quality is as important as additives for long-term viscosity retention
Oil viscosity index is an important parameter to measure oil performance and has an important impact on engine lubrication, hydraulic transmission and other fields. Increasing the viscosity index of oil can have significant advantages in improving the lubrication performance of equipment, reducing energy consumption, and improving efficiency. Therefore, this article will explore how to improve the viscosity index of oil, including its concepts, influencing factors and improvement methods.
The concept of oil viscosity index
Oil viscosity index refers to the ratio of the viscosity of an oil under certain temperature conditions to the viscosity of a standard reference oil. Viscosity refers to the strength of the intermolecular interaction of a liquid when it is subjected to shear force, while the viscosity index is a physical quantity that represents the degree to which the viscosity of an oil changes with temperature. The higher the viscosity index of the oil, the smaller the change in viscosity of the oil when temperature changes, so it has better high-temperature lubrication performance and lower energy consumption.
Factors affecting oil viscosity index
Temperature: Temperature is one of the main factors affecting the viscosity index of oil. As the temperature increases, the interaction between oil molecules weakens and the viscosity decreases. Therefore, equipment working at high temperatures needs to use oil with a higher viscosity index to ensure good lubrication and protection.
Oil types: Different types of oils have different chemical compositions and molecular structures, and therefore have different viscosity indexes. Generally speaking, synthetic oils have a higher viscosity index than mineral oils, so they are often a better choice in harsh operating conditions such as high temperatures and pressures.
Production process: The production process also has a certain impact on the oil viscosity index. For example, the viscosity index of an oil can be improved by adjusting its molecular structure and chemical composition during the refining process.
Methods to improve oil viscosity index
Use high-quality base oils: Different base oils have different viscosity index values. By choosing a carrier oil with a higher natural VI, you can increase the VI of your final oil blend.
Optimize oil formulations: By carefully selecting and blending different base oils and additives, you can create formulations that maintain stable viscosity over a wide temperature range.
Choose the appropriate production process: During the production process, by adjusting the production process and formula, the molecular structure and chemical composition of the oil can be changed, thereby improving its viscosity index. For example, the deep refining process can remove impurities and wax components in oil and reduce the viscosity index, while adding an appropriate amount of polymer additives can increase the viscosity of the oil, thus improving its viscosity index.
Adding additives: Additives can improve the viscosity and viscosity index of oil. For example, the addition of polymers, organic metal compounds and other additives can increase the molecular weight of oil and improve its viscosity and viscosity index. At the same time, some antioxidants, preservatives and other additives can also improve the oxidation stability and anti-corrosion performance of the oil and extend the service life of the oil. The use of shear stabilizing additives helps to improve VI by ensuring that the viscosity of the oil remains stable under certain conditions. Shanghai Minglan Chemical Co., Ltd. has VI improving additives that can improve the VI of lubricants. These additives help reduce the rate of change in viscosity with temperature.
Use synthetic oil: Synthetic oil has a higher viscosity index and a wider operating temperature range, so it can show good lubrication properties at both high and low temperatures. In situations where high-temperature lubrication is required, the use of synthetic oil can improve the lubrication effect and efficiency of the equipment.
Avoid contamination and oxidation: Regular oil analysis and maintenance can help identify and resolve contamination and oxidation problems. Unwanted contaminants and oil degradation can negatively impact VI, so it is critical to keep the oil clean and within recommended operating conditions.
Improving the viscosity index of oil is of great significance to the lubrication, energy saving and efficiency of equipment. By selecting appropriate production processes, adding additives, and using synthetic oils, the viscosity index of oils can be improved to a certain extent. However, these methods are not isolated, but require comprehensive consideration of factors such as the use, working conditions, and chemical composition of the oil. With the continuous development of science and technology, I believe that there will be more efficient, environmentally friendly and economical methods to improve the viscosity index of oil in the future, making greater contributions to the lubrication and energy saving of equipment.
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