Why High-VI Base Oils Win Across Temperature Ranges

Lubricating oil is generally composed of base oil and additives. Base oil is the primary component of lubricating oil and determines its fundamental properties. High viscosity index (VI) is a core indicator of high-quality base oil.

What is Viscosity Index?

Viscosity Index (VI) is a dimensionless numerical value used to measure the extent to which a lubricating oil's viscosity changes with temperature. A higher VI indicates a smaller change in viscosity relative to temperature changes, resulting in more stable lubricant performance across a wide temperature range.

Why Pursue a High Viscosity Index in Lubricant Base Oils?

Ensures Lubrication Protection under High-Temperature Operating Conditions (Prevents Excessive Thinning)

At running temperature, a low-VI oil thins toward the edge of its film. High-VI oils drop less viscosity, so the oil film between sliding surfaces stays intact where a low-VI product would start metal-to-metal contact. The same thermal margin cuts oxidation: less carbon, less sludge, slower degradation, longer service life.

 

Ensures Smooth Operation under Low-Temperature Conditions (Prevents Excessive Thickening)

At low temperatures, high-VI oils exhibit smaller viscosity increases, maintaining good low-temperature fluidity and pumpability, which reduces cold-start wear and energy consumption.

 

Enables Multigrade Oil Capabilities and Broad Operating Condition Adaptability

High-VI oils hold their viscosity from cold start to running temperature. One grade covers both low-temperature startability and high-temperature film protection, so operators can drop the seasonal oil swap that single-grade oils still demand.

 

Enhances Overall Lubricant Performance and Service Life

High-VI base oils hold their viscosity across a wide temperature range. They tend to resist oxidation, evaporate less at high temperatures, and keep components cleaner - which suits high-temperature, high-pressure, and high-speed service while extending drain intervals.

 

How to Enhance the Viscosity Index of Lubricant Base Oils?

The core pathways to enhancing the Viscosity Index (VI) of lubricant base oils include optimizing base oil quality, incorporating viscosity index improvers, and optimizing formulation design. Optimizing Base Oil Quality (Modifying Molecular Structure)

1. Mineral oil hydro-upgrading: converting low-VI molecules (aromatics, naphthenes, and normal paraffin wax) into high-VI molecules (isoparaffins).

 

Process	Key Reaction	VI Improvement
Hydrofining	Aromatics→Cycloalkanes (Hydrogenation Saturation)	+10~15
Hydrocracking	Ring opening & Isomerization of Cycloalkanes	+15~20
Isomerization Dewaxing	Normal Paraffins→Isoparaffins (Same Carbon Number)	+10~15

 

 

2. Selecting Synthetic Base Oils (directly synthesizing high-VI molecular structures from monomers)

 

Type	Molecular Design Strategy	VI
PAO	Olefin polymerization, controlling ramification degree + regular isoparaffins	130~150+
Diester	Dibasic acid+monohydric alcohol, ester linkage increases chain flexibility	140~155
Polyol ester	TMP/Neopentyl glycol + monobasic acid, quaternary carbon center inhibits crystallization	140~160+
PAG	Epoxy alkane ring-opening polymerization, ether bond provides extreme chain flexibility	160~220+

 

 

Chorus provides a wide variety of high-Viscosity Index (VI) synthetic base oils for the lubricant industry. Used as base oils or co-base additives, these synthetic esters are formulated into a broad spectrum of lubricant products, including engine oils, hydraulic fluids, aviation lubricants, compressor oils, chain lubricants, gear oils, and other industrial lubricants. Welcome to contact us for detailed technical specifications and the latest price quotes.

 

Adding Viscosity Index Improvers (Formulation Enhancement)

 

Adding VI Improvers (VII): Incorporating viscosity index improvers into base oil is the fastest and most effective method. Through their characteristic "expansion" at high temperatures and "contraction" at low temperatures, VIIs improve the oil's viscosity-temperature performance, compensate for the base oil's significant viscosity variations across temperatures, and maintain viscosity stability.

 

Blending Polyalphaolefins (PAO) with Esters

Utilize the polarity-regulating effect of esters to enhance both the VI and additive compatibility of PAO.

 

Polymethacrylate (PMA)

Offers strong thickening efficiency and excellent low-temperature performance, making it suitable for a wide temperature range.

Olefin Copolymer (OCP)

Provides good thickening power and high shear stability, well-suited for multigrade internal combustion engine oils.

 

Polyisobutylene (PIB)

Delivers excellent shear stability, but features relatively poor low-temperature performance, requiring balanced formulation.

 

Controlling Dosage Appropriately
Adjust the treat rate of the VI improver (typically around 4%–9%) based on base oil viscosity, target VI value, and application scenario to prevent excessive addition that could cause high oil thickness or degraded shear stability.

 

Chorus supplies a wide range of viscosity index improvers, including polymethacrylate (PMA), polyisobutylene (PIB), olefin copolymer (OCP), hydrogenated styrene-diene copolymer (HSD), and polyalphaolefin (PAO), which are widely used in engine oils, hydraulic fluids, and gear oils. Please contact us for the latest pricing.

 

Optimizing Formulations and Processes (Synergistic Enhancement)

 

Achieve a balance between base viscosity and overall VI enhancement by blending high-VI and low-VI base oils (such as PAO and mineral oils) in precise proportions. Concurrently, select VIIs with good compatibility to work synergistically with additives like antioxidants to inhibit high-temperature degradation, thereby realizing long-term stability of the viscosity index.

 

What is a Viscosity Index Improver?

 

A Viscosity Index Improver (VII) is an oil-soluble, long-chain polymeric compound, which includes polymethacrylate (PMA), polyisobutylene (PIB), olefin copolymer (OCP), hydrogenated styrene-diene copolymer (HSD), and polyalphaolefin (PAO).

 

Core Performance Comparison of the Five VII Types

 

Performance Indicator	PMA	PIB	OCP	HSD	High Viscosity PAO
Thickening Ability	★★★ Medium	★★★★ Good	★★★★★ Highest	★★★★ Good	★ Low
Shear Stability (SSI)	25 –35% Good	15–25% Excellent	35–45% Medium	15–20% Outstanding	<5% Permanently Stable
Low Temperature Fluidity	★★★★★ Optimal	★ Poor	★★★ Average	★★★ Average	★★★★★ Excellent
Thermal Oxidation Stability	★★★★ Good	★★★ Good	★★★ Average	★★★★★ Outstanding	★★★★★ Excellent
Demulsification Effect	★★★★★ With Both Coalescence	★ None	★ Poor	★ None	★★★ Certain Degree
Cost	High	Medium	Lowest	High	Highest