PAO Oil / Polyalphaolefin

Table of Contents

PAO, or polyalphaolefin, is one of the most common base oils for lubricants. Also, PAO oil is generally superior to mineral oil in terms of stability and other characteristics. Understanding these characteristics will help you succeed in choosing and using the ideal PAO-based lubricants for your specific lubrication needs.

What is PAO Oil?

Polyalphaolefin oil is a type of synthetic or “man-made” lubricant. Developed in the 1930s, PAO oil’s first commercial use was in the 1970s as a base for engine oils. Since then, PAO oil applications have reached a broader range. Current PAO oil applications include compressor, hydraulic, and turbine fluids, gear oils, and metalworking fluids.

The manufacturing of PAO oil involves a two-step process: synthesis and hydrogenation. First, alpha-olefins are used to synthesize oligomers. Next, the double bonds in these oligomers are hydrogenated to form polyalphaolefin. The PAO is further isolated by distillation to remove the unhydrogenated oligomers.

Characteristics of PAO Oil

The suitability of PAO oil as a base for lubricants comes from its properties and characteristics, including:

High Viscosity Index (VI)

Synthetic oils such as polyalkylene glycol, PAG oil, and PAO oil have a high viscosity index. A PAO-based lubricant has a naturally high VI and does not need additives to improve its VI. A high VI means that PAO-based lubricants can withstand high and low-temperature conditions without drastic changes in viscosity and performance.

Low Volatility or High Flash Point

PAO oil has a low volatility or tendency to evaporate. This resistance to evaporation means lower oil usage, which means less frequent refilling or replenishment. This low volatility also comes with a high flash point, which makes PAO-based lubricants less likely to oxidize or catch fire when exposed to high temperatures.

Low-Temperature Fluidity  

PAO oil maintains low viscosities even at low temperatures. This beneficial lubricant property is also described as having a low pour point. In simpler terms, PAO-based lubricants are least likely to become too thick even at freezing temperatures.

High Oxidative Stability

PAO oil is stable against oxidation which is the root cause of oil degradation and subsequent machine damage. High-temperature oxidative tests show that PAO-based lubricants can maintain viscosity and prevent sludge formation better than mineral oils.

Excellent Corrosion Stability

Due to its high oxidative stability, PAO oil shows excellent resistance against corrosion. This property makes PAO-based lubricants ideal for machine parts that experience constant exposure to high heat, water, and dirt. 

PAO Oil and Mineral Oil Compatibility 

Among all synthetic base oils, PAO oil has the highest compatibility with mineral oil. PAO oil’s high solubility in mineral oil makes it ideal to use in machines that also use mineral oil-based lubricants. This compatibility means that changing between these lubricants would not require costly cleaning or laborious methods. 

Seal and Paint Compatibility

Because of its solubility in mineral oils, PAO oil is also compatible with mineral oil-based seals and paints. Thus, there is no danger of damaging the critical seals and paints of your machine when using PAO-based lubricants. 

Disadvantages of PAO Oil

PAO oil is one of the top choices as a base oil for lubricants for its cost-effective and safe properties. But, there are also important downsides to using PAO oil-based lubricants, including:

Limited Biodegradability

Most grades of PAO oil are not biodegradable and require careful handling. Improper storage, use, and waste disposal of PAO-based lubricants may result in harmful effects on the environment. Refer to the manufacturer’s storage and handling instructions or current local regulations when using PAO-based lubricants.

Limited Additive Solubility

PAO oil’s low polarity makes it difficult to dissolve a wide range of lubricant additives. It is a common practice for lubricant manufacturers to blend PAO oil with other base oil types with higher polarity. This practice lets common anti-wear and viscosity additives become more soluble in PAO oil.

Seal Shrinkage Risk

Another downside to using PAO oil is its tendency to allow the shrinking of elastomers in seals. Esters are often added to a PAO-based lubricant formula to compensate for this negative property.

Limited Wear Properties

Compared to other synthetic lubricant base oils, PAO oil has limited wear properties. Thus, PAO-based lubricants are best for rolling wear protection, like on bearings or similar disk-like surfaces.

Is PAO Oil an Ideal Lubricant for Your Lubrication Systems?

The success of your lubrication system depends on your choice of lubricant. But, because every lubricant works differently to varying lubrication systems, you have to have a system that monitors the performance of your chosen lubricant. Redlist’s Lubrication Management Software is a tool that can ensure the success of your lubrication system. If you’re curious as to how we can do this for you, a free demo is just a click away!

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