Can You Mix Synthetic Gear Oil & Regular?

Gear oil is thick (high viscosity), heavy oil that is used to reduce friction, heat transfer and corrosion in units containing gears. Manmade or synthetic gear oils reduce engine wear and can be pumped to critical surfaces faster than regular, mineral (petroleum-based) oils.

Types of Synthetic Gear Oil

There are essentially two different types of synthetic gear oil, polyalphaolefin (poly-alpha-olefin), or PAO and polyalkylene glycol, or PAG. PAO oils are, in fact, enhanced versions of regular mineral oils and can be mixed freely with them.

Mixing

Indeed, some commercially available gear oils are a mixture of synthetic PAO oil and mineral oil in various proportions. This is a clear indication that synthetic and regular mineral gear oils can be mixed.

Polyalkylene Glycol

PAG oils, on the other hand, are polymers formed by the addition of ethylene or propylene oxide molecular units, or monomers. They offer superior performance when compared with mineral oils, but cannot be mixed with them.

References

• "Petroleum Fuels Manufacturing Handbook"; Surinder Parkash; 2009
• BASF: Performance Benefits of Polyalkylene Glycols in Lubricants