Gear oils’ main objective is to provide lubrication for the gear system. They protect the transmission and gearboxes’ internal parts from wear, tear and excess heat. 

These lubricants serve to provide smooth functioning of the gears and bearings in the drive axles and differentials. They also help enhance the functioning of the gear set and the overall smooth operation of your vehicle

Gear oils work on transmissions, transfer cases, trucks, automobiles and other machinery differentials. They lubricate to give result to a seamless and hassle-free running of the gearbox.

These are high viscosity fluids that provide resistance against damage to critical parts of the gear system. Depending on various additives in them, gear oils provide specific properties and add to the performance of your car. 

The Ultimate Gear Oil Guide

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How Does Gear Oil Work?

Before we understand how gear oils work, let us briefly talk about gears. The gear system of your car includes a gearbox, propeller shafts, hypoid bevel gears, transmissions, live axle, bearings etc. Gearboxes in vehicles execute three primary functions. The first is the transmission of power from the crankshaft to the driveshaft.

Eventually, this powers and propels the wheels of your car. Secondly, it is also an application of speed and how drivers can control it. It helps you increase the speed of the vehicle along with the force. The third is about direction. Gearboxes will help change the direction as well as the force of the power with the help of the differentials.

As mentioned earlier, the gear system consists of critical parts which need proper lubrication so that there is no direct contact. This reduces undesired friction and wear. Moreover, gear oils are high in viscosity and often consist of organosulfur compounds. They lubricate and protect these internal parts to perform the above three functions smoothly. 

One of the main aspects to consider here is the viscosity of gear oils. Viscosity is a fluid’s resistance to flow. Gear oils tend to have thick film strength to allow adequate protection to the gear parts, resist wear damage and perform well at high pressure. 

That said, a change in temperature influences a change in viscosity and as these oils are high in viscosity, they resist thinning out at high temperatures. 

At normal temperatures, gear oils run from around 50℃ to 55℃. Lubricants that are operating on higher temperatures need to have a good viscosity and protection against foaming and oxidation. 

At extreme temperatures, mineral-based gear oils can be prone to breaking down. This results in lesser lubrication and gradually, leads to oil deterioration. 

For manual transmission, gear oils are far thicker in viscosity because of the amount of friction and heat generated in these gear systems. 

Thus, oils for this type of transmissions are manufactured to resist high temperatures and perform effective lubrication. On the other hand, automatic transmissions require automatic transmission fluids, ATFs. They cannot be used interchangeably.

What Are The Types Of Gear Oils?

Essentially gear oils need to have certain properties. For instance, they need to be adhesive to be able to stick to the metal surface and prevent wear. 

There also needs to be foam inhibition to allow smooth gearing. This is where antifoam agents resist foam formulation which is because of the rigid action of the gears. 

Third, low emulsion formation to tackle oxidation of the oil. Along with this, gear oils are also identified by their additive makeup. 

R & O (Rust and Oxidation) Gear Oils

Specially designed for corrosion reduction in the gearbox, they operate with regard to chemical stability, suppressing foam and demulsibility. Many gear oils are equipped with corrosion-reducing qualities.

EP (Extreme Pressure) Gear Oils

Also known as anti-scuff lubricants, these contain more superior properties as compared to R & O gear oils. They also endure extreme conditions heat and pressure. 

Compounded Gear Oils

Gear oils are mixed with fat (synthetic fatty acids) for better lubricity and film strength. These work well for high-pressure applications, low speeds and ensure good quality lubrication.

Synthetic Gear Oils

Synthetic gear oils are used in extremely high/low temperatures as well as high loads. These consist of a lower friction coefficient and an effective relationship between viscosity and temperature. 

Gear oils have a base oil depending upon whether you require mineral or synthetic. The base oil quality matters significantly to ensure your gear system functions ideally. 

Furthermore, these oils are mostly mixed with additives to promote the protection and performance of the gearset. They are as follows;

  • Extreme Pressure additives (EP)
  • Anti-wear additives 
  • Oxidation inhibitors
  • Rust and corrosion inhibitors
  • Antifoam agents
  • Pour-point depressants
  • Dithiocarbamate derivatives
  • Sulfur-treated organic compounds


Gear oils have a crucial motive to perform so that you get the smooth operation from your car, truck or any geared vehicle or machinery. Additionally, it is always better to be well-informed of the workings and properties of these lubricants.

Another important thing to note here is the OEM; Original Equipment Manufacturer recommendations. 

There are many gear oils that you think might work well for your gear system but it would be advantageous to use the one suggested by your vehicle owner or the one mentioned in the vehicle manual. 

To achieve the best running and driving experience, always use the lubricants recommended in the manual.  



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