Hydraulic Fluid vs. Transmission Fluid – What Are The Differences?

Hydraulic fluid and transmission fluid are essential to the operation of automotive systems and are sometimes used interchangeably. There are some critical differences between the two fluids. We have done our research to find those differences. 

The main difference between hydraulic and transmission fluids is that hydraulic fluid transmits power while transmission fluid lubricates and cools the transmission. Hydraulic fluid is also a medium for heat exchange in some hydraulic systems, but transmission fluid doesn't have this property.

Using the correct type of transmission fluid in a vehicle, like hydraulic fluid, is essential. Keep reading to learn more about the significant characteristics and differences between these two fluids. 

What Is The Difference Between Hydraulic and Transmission Fluid? 

Repairman's male hands pouring brake fluid into the brake tank.

Hydraulic fluid and transmission fluid are two lubricants used in different vehicle parts. They differ in their functions.

Hydraulic fluid is for hydraulic systems, such as brakes and power steering systems. It transmits power by using pressurized fluid. Transmission fluid, on the other hand, is an oil that lubricates the transmission's moving parts. It transfers power from the engine to the transmission. 

Both oils have different characteristics that make them suited for their respective tasks. We explain some of these below. 

Characteristics Of Hydraulic Oil

Hydraulic oil is available in various grades and types, each designed for specific applications. The most common grades are mineral oil, synthetic oil, and biodegradable oil. 

Mineral-Based Hydraulic Oil

Mineral-based hydraulic oil is a type of hydraulic fluid made from mineral oil, a liquid petroleum product. It is commonly used in various industrial and mobile hydraulic systems because it is relatively inexpensive and has good lubricating properties.

Mineral-based hydraulic oil is refined crude oil without impurities. It is generally stable over a wide range of temperatures and has a long shelf life.

Still, it can break down and become less effective over time, especially if it is subjected to high temperatures or contamination.

Synthetic-Based Hydraulic Oil

Synthetic hydraulic oils are lubricants made from artificially produced chemical compounds rather than naturally occurring mineral oil. Manufacturers design them to offer improved performance and longer service life than mineral-based hydraulic oils.

Synthetic hydraulic oils have several advantages over mineral-based hydraulic oils. They tend to have a wider temperature range and are less prone to breakdown and degradation.

Check out this Quicksilver hydraulic oil on Amazon.

Biodegradable Hydraulic Oil

Biodegradable hydraulic oil is a type of hydraulic fluid made from natural materials that can decompose. It is less environmentally harmful than traditional hydraulic oils. Biodegradable hydraulic oils are typically made from plant-based materials, such as soybean oil.

They have similar lubricating properties as traditional hydraulic oils. But they are less toxic and can be broken down by bacteria and other environmental microorganisms.

Characteristics Of Transmission Oil

Transmission oil is typically a high-viscosity oil, and its primary purpose is to lubricate moving parts and prevent wear. Transmission oil sometimes contains additives that protect against corrosion and improve its performance.

There are two major types of transmission oils: automatic transmission fluid and manual transmission fluid. 

Automatic Transmission Fluid

Automatic transmission fluid (ATF) is a lubricant used in automatic transmissions. It lubricates the transmission's moving parts and transfers power from the engine to the transmission.

It also serves as a hydraulic fluid, helping to operate the transmission's internal clutches and brakes. ATF is typically made from a blend of base oils and additives and is available in different formulations, usually green or red. 

Click here to see Valvoline synthetic transmission fluid on Amazon.

Manual Transmission Fluid

Manual transmission fluid (MTF) is a specialized oil formulated to meet the specific requirements of a manual transmission. It is fully synthetic and is usually used in gearbox transmissions. 

Can You Mix Hydraulic Fluid With Transmission Fluid? 

Male hand filling car power steering fluid

You should not mix hydraulic fluid and transmission fluid. Hydraulic and transmission fluids are different fluids that serve different purposes in a vehicle.

Mixing these two fluids can damage the braking system and the transmission, leading to expensive repairs. If you are unsure which type of fluid to use, consult your vehicle owner's manual or a qualified mechanic.

Can You Use Automatic Transmission Fluid In A Hydraulic Jack? 

Car mechanic drain the old automatic transmission fluid (ATF) or gear oil at car garage for changing the oil in a gear box of car engine

Jack oil is a hydraulic fluid utilized for power production, sealing, heat transmission, lubrication, and other purposes. You can use automatic transmission fluid in a hydraulic jack. However, there are some factors you should keep in mind.

First, hydraulic jacks use hydraulic oil, so using transmission fluid may cause some problems. Transmission fluid is not as thick as hydraulic oil, so it may not provide the same level of lubrication.

Is Hydraulic Fluid The Same As Engine Oil? 

No, hydraulic fluid is not the same as engine oil. Hydraulic fluid is a type of mineral oil, while engine oil is a petroleum-based lubricant used to lubricate and cool engines.

It reduces friction and wear between the engine's moving parts and helps keep the engine cool by dissipating heat. While hydraulic fluid and engine oil are lubricants, they are formulated differently to meet the specific requirements of their respective systems.

What Is A Good Substitute For Hydraulic Fluid? 

Mechanic filling red hydraulic oil in service shop

Although using other fluids as a substitute for hydraulic fluid is possible, choosing a replacement compatible with the system is essential. It ensures that there's no damage to the vehicle.

Here are some of the best substitutes for hydraulic fluid: 

Check brake fluid,Hand open a tank for car maintenance., Hydraulic Fluid Vs. Transmission Fluid: What Are The Differences?

Brake Fluid

Brake fluid often acts as a substitute for hydraulic fluid. However, it is important to note that brake fluid is not a genuine hydraulic fluid and can only be used in specific applications. Additionally, brake fluid is typically more expensive than hydraulic fluid. 

Vegetable Seed Oil

In some cases, vegetable seed oil can replace hydraulic oil. Please remember that vegetable seed oils may not have the same performance characteristics as traditional hydraulic oils, especially at high temperatures or extreme conditions.


Water is a good substitute for hydraulic fluid because it is incompressible and has a high specific heat capacity. It can absorb heat without changing temperature, which is vital in hydraulic systems because they generate a lot of heat. Water is also a good lubricant, which helps to protect the components in the system from wear and tear.

Why Does Hydraulic Fluid Change Color? 

Hydraulic fluid can change color for a variety of reasons. Some of the most common causes include:


The fluid can become discolored if foreign substances like dirt enter the system. The color of the contamination will affect the color of the fluid. For example, liquid contaminants can make it a milky-brownish color.


Over time, hydraulic fluid can degrade and lose its original color. The fluid may darken or develop a yellow or brown tint as it becomes contaminated with metal particles or other materials.

Thermal Stress and Oxidation

High temperatures can cause the fluid to change color, often making it appear darker or more opaque. Certain chemical reactions can also cause the fluid to change color. For example, the fluid may turn dark if exposed to oxidation.

It is important to note that color change is not a definitive indicator of a problem in the system. To be sure, perform other diagnostic tests, such as viscosity checks, water detection, or particulate counts, to determine the system's health.

To Wrap Up

There are a few critical differences between hydraulic fluid and transmission fluid. Hydraulic fluid is a non-compressible fluid, which makes it ideal for use in hydraulic systems where high pressure is required.

Transmission fluid, on the other hand, is a compressible fluid used in transmissions to help transfer power from the engine to the wheels.

Check out other engaging articles relating to automotive fluids: 

What is The Best Oil For a 2 Stroke Transmission?

Does Hydraulic Fluid Go Bad?

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