Are PAO’s the best synthetic base stock oil for engine oils?

Although PAO’s are commonly used, are they really the best synthetic base stock for engine oil? And why are PAG’s not commonly used as synthetic base stock for engine oils?

Polyalkylene glycols or PAG base oils are types of synthetic base stocks. While synthetic engine oils are becoming
increasingly common, they usually are not formulated with this type of base oil stock. (PAG)

While not traditionally used in engine oils, PAG oils are very common in refrigeration oils, brake fluids and various gear oils. That’s not to say that PAG oils can’t be used in engine oils.

Most engine oil base stocks are polyalphaolefin or PAO base oils, with some being synthetic blends. Blending of synthetic oils is a precise science and is normally done to aid in the formulation with additives.

Why would PAG’s be the best synthetic base stock for engine oil?

There have been studies done using these types of synthetics for all types of automotive lubricants including gear, transmission and crankcase oils.

Synthetic engine oils across the board offer a wide array of benefits in any application. More often than not they have a higher oxidative and temperature tolerance, so they last longer in service.

In mobile equipment that operates in extreme temperature environments, synthetics work extremely well as they generally have a higher viscosity index.

The viscosity index is a measure of how much viscosity changes over a temperature range. The higher the value, the less the viscosity is affected by a change in temperature.

PAGs have excellent lubricity and a high viscosity index (typically 100 to 200, depending on the formulation). They also have great thermal and oxidative stability. This equates to longer service life and functionality when used in high-temperature applications.

Beware of the following when using engine oils with PAG base stock.

Along with benefits, there are also drawbacks for any synthetic.

PAG based synthetics have the dubious reputation of not being miscible with mineral oils.

PAG and standard mineral oils do not mix well and form a thick toffee-like substance when they come in contact with each other.

Not only can they not mix with mineral oils, but certain polymers and paints are also incompatible with these fluids. PAGs can cause the shrinking or swelling of some seal materials, which can lead to leaks and/or allow contamination into the system.

Before using PAG oils in any machinery (engine, gearbox, hydraulic system, etc.), make sure all the materials are compatible. Likewise, if the system was previously filled with a mineral oil, the system should be flushed to ensure that all the mineral oil is removed to avoid any of the previously mentioned problems.

So while synthetics are becoming more and more widespread, different synthetics are used in different applications.

One of the biggest risks when switching from a mineral oil to a synthetic oil is the incompatibility. This should always be kept in mind.

If you have any questions about using synthetic engine oils, don’t hesitate to contact Habot Synthetic Lubricants for the best products and advice.