Best Synthetic Oil for Gear Box Lubrication | Mineral Oil Vs Synthetic Oil.


In this article, we are discussing the best synthetic oil for gearbox lubrication. We have already discussed Mineral Oil Vs. Synthetic oil & which is better to use in industrial gearboxes. So, today we will discuss which synthetic oil is best suited for high-loaded & slow RPM gearboxes.

Types of Synthetic Lubricants

Approximately 80% of synthetic lubricants used in the world are of three types. In order of volume used, they are polyalphaolefins (PAOs), organic esters, and polyglycols. The remaining synthetic lubricants are produced from other base stocks, including phosphate esters, polybutenes, silicones, perfluoroalkyl, and polyphenyl ethers.

So, in this article we will talk about two types of synthetic oil which is mainly available in the market & used by majority of industry peoples.


Polyalphaolefin (PAO) fluids are the most common major synthetic base oil used in industrial and automotive lubricants. These synthetic hydrocarbons provide superior lubrication performance over a wider operating temperature than petroleum oils and are typically less volatile. In addition, PAO-based lubricants generally resist creep and water washout and offer good lubricity across various substrate material pairings, including metal-to-metal and metal-to-plastic.

PAO fluids are classified as a Group IV base oil and are made by a two-step reaction process using linear alpha-olefins like 1-decene. The first step is the synthesis of oligomers (polymers with few repeating monomer units) from the linear alpha-olefin. The second step is to hydrogenate the remaining double bonds (unsaturation) in the oligomer and subsequent distillation to separate the unreacted monomer and light-viscosity grade PAO.

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Polyalkylene glycol and polyglycol are used interchangeably. These fluids can be manufactured to be either water-soluble or water-insoluble (oil soluble). The most common are the water-soluble fluids, and thus they can have some very different properties. Polyglycols are moderately polar, which gives them moderate film strength properties. In addition, they have a very high viscosity index (180 to 280) and can sustain its lubricating properties at low and high temperatures.

PAG base stocks are classified as a Group V oil, meaning a synthetic basestock that is not defined as a Group I, II, III, or IV base oil. Group V oils also include esters and naphthenic oils. PAG-based lubricants are commonly used in compressors, gearboxes, air conditioning systems, metalworking, quenching, and hydraulic systems where fire resistance or environmental acceptability are required.

Reasons to change from mineral oil-based lubricants to synthetics despite the increase in cost include:

  • Need fill-for-life lubricant or high relubrication interval.
  • Extend equipment life with less downtime. Increase production rate.
  • Meet regulations (fire resistance, environmental acceptability).
  • Address specific system site conditions (potential for water ingression).
  • Address new equipment conditions (higher operating temperature and pressure, greater loads and speed).
  • Heavy Load on the gears of the gearbox. Need lower co-efficient of friction gear oil to reduce the high proportion of sliding friction & maximize the gearbox service life.
  • Prevention of acidity, sludge, deposit formation.
  • Excellent protection against rust and corrosion, even during the shutdown.
  • Good foam control & higher wear protection.
  • Lower gearing losses due to reduced friction lead to lower energy costs.
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We have now understood that there are two types of synthetic oil available & understood the basic definition of synthetic oil. Now we will discuss which oil is best suited for gearbox lubrication & how you can choose the best oil for your gearbox lubrication, which can ultimately increase the gearbox life with high relubrication intervals.

How to select Polyglycol oil for gearbox lubrication?

Polyglycol oils are not compatible with any mineral or synthetic-based oil. So, when selecting Polyglycol oil, you must check the below-mentioned checklists.

Compatibility with the inside paint of the gearbox should be checked. Normal machine paints dissolve in contact with PAG oil. However, almost all reaction-hardening two-component epoxy resin paints are resistant to PAG oil.

Seals based on Nitrile rubber, also known as NBR , Hydrogenated acrylonitrile butadiene rubber (HNBR) and FKM (Fluro-Elastomer) are normally resistant up to the operating temperatures stated by the manufacturer for the elastomer or the PAG oil, e.g., up to 100 °C.

Positive results have been attained with 72 NBR 902 and 75 FKM 585. For other materials, compatibility should be tested, especially when they are to be used in dynamically loaded seals.

Oil gauge glass should preferably be made of natural glass or polyamide materials. Other transparent plastic materials such as plexiglass tend to be stress-cracking.

The filter elements should be replaced after the oil change and flushing. The filters used should be made of glass fiber or metal fleece. Paper filters tend to swell and clog rapidly.

When you are changing from mineral to PAG oil, if you do not go through the above checklist or situation is that you cannot go through the above list, you may go with PAO-based synthetic oil, which is compatible with all kinds of mineral oil & also does not have any bad effect with different types of gearbox internal paints & seal rubbers.

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Hope you have liked our article. Do share with your colleagues & friends who are always eager to learn something new about lubrication.

Also read:

What is Tribology, Tribosystem & Lubrication

Basics of Industrial Lubricants.

Lubricating Oils Vs Lubricating Greases | What to Choose & Why?


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