Gear Oil

Gear oil and hydraulic oil are both types of lubricating oils, but they are designed for different applications and have distinct properties to suit their respective functions.

The main function of gear oil is to protect the gears that are working under high pressure and at high speeds.


Gear oils, which are available in many combinations, are used for lubricating gear contacts with the sliding and rolling motions used in industrial equipment, automobiles, and other machinery.
The oil exhibits anti-friction properties while it cools and removes the heat that originates with the friction between the parts.
Lowly loaded spur gears need only oils that provide protection against rust and oxidation, whereas, the heavy loaded ones need high levels of EP additives.
Higher-viscosity oils protect the gears well and transfer the lubricant throughout the gear train smoothly.
Such oils have a strong smell of sulphur due to the additives present in them, which helps maximum pressure protection.
The oils that contain EP (extreme pressure) additives have phosphorus or sulphur compounds and are corrosive to yellow metal bushings and synchronizers.
The GL-1 (Gear Lubricant-1) gear oils do not have any EP additives, and so they are used for applications on parts made of yellow metals, such as copper and brass.

What is the difference between gear oil and hydraulic oil

Gear oils are classified into several groups as per the GL ratings.
The advanced gear boxes require GL-4 oils; and, therefore, while selecting gear oils, it is good to ensure that they conform to the manufacturer’s specifications.
Today fully synthetic gear oils are used in vehicles, as they show more resistance to shear breakdown than the mineral oils.
However, high quality mineral oils are the best options, for they are thicker, having better viscosity coefficients than the synthetic gear oils. Identifying the appropriate gear oil for a specific application lies in evaluating viscosity, base oil, and the lubricant.

Hydraulic Oil

Hydraulic oil is a lubricating medium that transfers power through hydraulic systems, like excavator booms, hydraulic brakes, power steering systems, lift, etc.


It derives large amounts of energy using comparatively thin tubes and hoses.
The key elements of performance in quality hydraulic oils are their tough resistance to volume reduction under pressure and high viscosity.
To facilitate this, hydraulic oils are made of oils and additives to transmit the power smoothly and effectively while performing as lubricants and coolants as well.
Hydraulic oil can reduce wear, rust, and corrosion in hydraulic equipment. Since hydraulic oil is flammable, it is unsafe to bring it close to any ignition source.

In earlier times, fluid power mechanisms were run with water as the hydraulic medium.
Due to its corrosive nature and lack of lubricity, water was replaced by petroleum-based oil.
Water-in-oil emulsions are composed of emulsifiers, additives, 35-40% water, and 60% mineral oil.
Most of these mineral-oil hydraulic fluids are generated from dewaxed paraffin-based crude oil.
Additives are then added to get the desired properties.
Synthetic hydraulic fluids, which are fire resistant, are the latest in the array, finding places in more and more crucial hydraulic applications. Regardless of what is stated above,

The functions of hydraulic oils in any given application system can be summarized as:

(i) Transmitting power efficiently and cost-effectively
(ii) Lubricating the system
(iii) Resistance to foams
(iv) Capability to release air
(v) Thermal, oxidation, and hydrolytic stability
(vi) Resistance to corrosion, removing impurities, and anti-wear performance
(vii) Filterability
(viii) Heat dissipation
(ix) Viscosity
(x) Fire and flash resistance, and
(xi) Low coefficient of expansion and low specific gravity.

The key to predicting the behavior of a hydraulic fluid lies in the analysis of its viscosity while moving through a hydraulic system.
Low viscosity oils fail to seal properly, leading to pressure loss, seepage, and component wear. Fluids that are too thick will reduce the system’s efficiency.

Main difference between gear oil and hydraulic oil

Gear oil and hydraulic oil are both types of lubricating oils, but they serve different purposes and have distinct characteristics tailored to their specific applications.

Gear Oil

Purpose: Gear oil is specifically designed for lubricating gears and bearings in various types of gear systems, such as manual transmissions, differentials, and gearboxes.

Viscosity: Gear oils typically have higher viscosity compared to hydraulic oils. They need to maintain a stable film of lubrication between gear teeth under high-pressure conditions.

Additives: Gear oils often contain additives to enhance their extreme pressure (EP) properties, ensuring proper lubrication even under heavy loads and high temperatures.

Performance Characteristics: They are formulated to resist foaming and oxidation, providing effective lubrication in demanding conditions.

Hydraulic Oil

Purpose: Hydraulic oil is designed for use in hydraulic systems, such as those found in hydraulic machinery and equipment. These systems use fluid to transmit power and perform work.

Viscosity: Hydraulic oils generally have lower viscosity compared to gear oils. This allows them to flow easily through hydraulic components and maintain the desired pressure in the system.

Additives: Hydraulic oils may contain additives to improve anti-wear, rust and corrosion protection, and to enhance their overall performance in hydraulic systems.

Performance Characteristics: Hydraulic oils are formulated to provide consistent and reliable performance in a wide range of temperatures and operating conditions. They are also designed to transfer power efficiently without causing excessive wear on system components.


Can hydraulic oil be used as gear oil?
Typical hydraulic oils do not have these properties and cannot provide sufficient wear protection for the upper drivers of the gear teeth. Oils are usually formulated for use in specific applications. The right balance of additives provides the right protection for each application.

Are transmission oil and hydraulic oil the same?
Transmission oil is a type of hydraulic oil! It is a medium that transmits power from the engine to the transmission. Meanwhile, other types of hydraulic fluids include multigrade motor oil, conventional hydraulic oil and anti-wear.

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By Aditya

Hi, I’m Aditya Sharma, a professional blogger from Gurgaon, India and I launched this blog called aadityacademy on July 2021. is a mechanical Project-oriented platform run by Aditya sharma and I got the motivation to start aadityacademy blog after seeing less technical education information available on google.

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