Can You Use Transmission Fluid For Brake Fluid?

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Brake fluid and transmission fluid are both essential lubricants for your vehicle. When it comes to fluid changes, it is an expensive service. Some car owners think brake fluid and transmission fluid are same, but there are significant differences between these two products.

The braking system is one of the most critical parts of a car. You may be tempted to use brake fluid for the transmission system, hoping to save money. After all, they both perform similar functions. So, it is essential to know the difference between these two fluids and use them accordingly.

In this article, I’ll cover whether can you use transmission fluid for brake fluid? And transmission fluid and brake fluid are interchangeable. Moreover and brake fluid and transmission fluid the same or different?

Can you use transmission fluid for brake fluid

What is brake fluid?

The brake fluid is a hydraulic fluid that transfers pressure into force in brake systems. This, in turn, helps braking systems work. Brake fluid is made from glycol ether/borate ester or silicone. They are non-petroleum materials. However, there are few petroleum-based brake fluids that are not used widely. When the driver pushes the brake pedal, this fluid transfer the pressure into the pistons and uses force on the brake pads to stop or slow down the vehicle.

In the market, we can see different types of brake fluid. The most common fluids are DOT3, DOT4, DOT5, and DOT5.1. These different types of fluids have different viscosity and boiling point values.

Brake fluid is a hygroscopic fluid; It absorbs moisture, which helps absorb moisture that may build up in the brake system over time. This will help prevent the calipers from rusting.

Viscosity is another important part of brake fluid. Viscosity is the fluid’s resistance to flow (deformation). When the fluid has a lower viscosity, it moves quickly. The viscosity of the brake fluids is important because it affects the reaction of the braking system. When the brake fluid gets thicker, you have to replace it.

The boiling point is another critical part of brake fluid. When braking the vehicle, its calipers and pistons generate high temperatures, and brake fluid has a higher boiling point to prevent vaporization.



What is transmission fluid?

Transmission fluid is the oil used to transfer engine power to wheels and cool the moving parts of your car’s transmission. The fluid helps to keep the transmission system gear shifting smoothly and prevents the components from overheating. Transmission fluid is a hydraulic fluid made of petroleum, and synthetic transmission fluid is made of chemical base oil.

Over time, the fluid can be contaminated, so it’s essential to check it periodically and change it as needed. You should also avoid using brake fluid for the transmission system, as it can damage the seals and cause leaks. Like the engine fluid, the transmission fluid can tolerate high operating temperatures. Transmission fluid is not hygroscopic; therefore, it does not absorb water and dissolves water.



Can you use transmission fluid for brake fluid?

The simple answer is No; you cannot use transmission fluid for brake fluid. These two fluids are made of different base oil types; therefore, brake and transmission fluids are not the same. The braking system has many rubber seals; these rubber parts swell, deform or damage when using mineral-based oil, and this will cause brakes to stick or leak fluids from rubber seals.

Moreover, brake fluids have a lower viscosity than transmission fluids, which means brake fluids are thinner than transmission fluids. When the fluid gets thicker, it has a lower reaction time. When the brake fluids get thicker, you have to replace them.

The braking system generates friction when slowdown or stopping the vehicle, which produces more heat. Therefore brake fluid has a higher boiling point than the transmission fluid. When you use low boiling point fluids in a braking system, it thins the fluid at high temperatures and can cause wearing metal parts and damage the rubber seals and gaskets. Furthermore, it can be forming deposits and sludge in the system.


Reasons that transmission fluids cannot use as brake fluid?

  • Brake fluid is developed to withstand high operating temperatures than transmission fluid.
  • Brake fluid has more corrosion inhibitors than transmission fluid.
  • Transmission fluids have high viscosity than brake fluid. High viscosity means thicker.
  • Mineral-based oils can cause brake system leakage from rubber parts due to deforming. Therefore, the transmission fluid is unsuitable for the brake system.
  • Brake fluid is designed to absorb water, prevent corrosion, and maintain proper lubrication. Mineral-based transmission fluid does not absorb moisture.
  • These two fluids’ base oil is entirely different, brake fluid is glycol ethers or silicone (non-petroleum), and transmission fluid is either petroleum or full synthetic.



What is the difference between brake fluid and transmission fluid?

Brake fluid and transmission fluid are both critical fluids in your vehicle, and they both have different functions and should not be used interchangeably.


Base oil.

Brake fluid is made of glycol ethers and is designed to withstand high temperatures, and this is a hydraulic fluid.

Transmission fluid is made of petroleum as base oil and is designed to withstand high temperatures, and it is responsible for lubricating and cooling your transmission system.

Brake system rubber parts can damage when using transmission fluid, increases metal parts wearing, and cause your brakes to fail.



Brake fluids have a lower viscosity than transmission fluids. All the brake fluids have 1.5 mm2/s viscosity, and transmission fluids have over 5.0 mm2/s viscosity. High viscosity fluids travel slowly and are resistant to deformation.


Boiling point.

Brake Fluids: DOT 3 brake fluids have a 401°F (205°C) boiling point, and DOT 4 has a 446°F (236°C) boiling point. The DOT standard is one of the most commonly accepted brake fluid ratings—the Department of Transport (DOT) standard categories have minimum boil point requirements. DOT3 and DOT4 are the automobile industry’s most widely used brake fluids.

Transmission Fluids: We can find different transmission fluids brands with slightly different boiling points on the market. Most transmission fluids have a 356°F (180°C) boiling point, and fully synthetic transmission fluids have over 420°F (215°C) boiling point (on average). Unlike the DOT standard, we cannot find a minimum boiling point in transmission fluids (ATF or MTF). Therefore this comparison uses two popular different transmission fluids brands.

Difference: You can see in the following table that DOT3 and DOT4 have higher boiling points than the transmission fluid, which is a significant difference between these two fluids. So there is a substantial difference between these two types of fluids’ boiling points.

If your vehicle manufacturer recommended DOT3 fluids, you should not use higher boiling point transmission fluids (like full synthetic) because they have mineral oil-based properties, which can cause problems to rubber seals.


Transmission Fluids vs Brake Fluids.

Type of FluidType Boil PointViscosity at 212 °F (100 °C )Composition
Brake FluidDOT 3401°F/205°C1.5 mm2/sGlycol Ether
Brake FluidDOT 4446°F/230°C1.5 mm2/sGlycol Ether/Borate Ester
Brake FluidDOT 5.1500°F/260°C1.5 mm2/sGlycol Ether/Borate Ester
Brake FluidDOT 5500°F/260°C1.5 mm2/sSilicone
Transmission FluidCastrol Transmax DEX/MERC424°F/218°C5.9 mm²/sConventional fluid
Transmission FluidMobil™ Multi-Vehicle424°F/217°C5.85 mm²/sFull synthetic
Transmission FluidValvoline Professional428°F/220°C15.4 mm²/sFull synthetic



What happens if you use transmission fluid as brake fluid?

Using transmission fluids for the brake system can damage the brake pistons’ rubber parts. Furthermore, transmission fluids are quickly thin at high temperatures, increasing metal parts wearing and building up deposits and sludge. This may cause brake failure and frequent fluid contamination, and sometimes, it can void your insurance and car warranty.

If you use the wrong fluid for the braking system, immediately flush it with the correct brake fluid. This is necessary for safety and protects damaged parts.



Can I use hydraulic fluid for brake fluid?

If the brake fluid is a type of hydraulic fluid, you cannot use hydraulic fluids for brake fluid, and this can cause seals to swell up, ultimately damaging the barking system. Therefore if you use the wrong fluid, immediately flush out and replace the correct brake fluid.


Can you use engine oil for brake fluid?

You cannot use engine oil for the brake system. All types of engine oils (including synthetic engine oils) are made from mineral oil. Brake system pistons have a lot of rubber parts. Using mineral oil-based products in the braking system defoams, swelling, and damages these rubber parts. Therefore if you use engine oil as brake fluid, immediately flush it out.


Can I put power steering fluid in my brake fluid?

Power steering and brake fluids are hydropic but have different chemical properties. Power steering fluids are made of mineral oil, silicone, or chemical (synthetic) base material. And brake fluid is made of either Glycol ether, borate ester, or silicone.


Is brake fluid the same as transmission fluid?

No, brake and transmission fluids are different fluids that serve different purposes in your car. These two fluids are made from different base oils. Brake fluid applies hydraulic pressure to your brake calipers, while transmission fluid lubricates and cools the transmission’s moving metal parts. Mixing these two fluids can cause damage to your vehicle, so using the correct fluid for each system is essential.


Can I Use Motor Oil For Transmission Fluids?

No. You cannot use motor oil for the transmission system. These two lubricants are used for different purposes. Motor oils are thicker, and transmission fluid (ATF or MTF) is lighter. If you use motor oil for transmission fluid, it will end in costly repairs. Furthermore, you may experience sudden downshift or shift to a higher gear and shaking movements when changing gears.



You can not use transmission fluid for brake fluid. These two products use for different purposes and are not interchangeable. Brake fluids are slightly thinner than transmission fluids. Moreover, these two products’ base oil is entirely different. Transmission fluid is made of mineral oils, and brake oil is made of non-petroleum oils like glycol ether/borate ester or silicone.

The brake system has a lot of rubber parts in the pistons. When using mineral oil-based fluids, these rubber parts defoam and damage. It can ultimately cause braking failure or leaking of fluid. Furthermore, it can void your car warranty and insurance policy.

If you mix transmission fluid with brake fluid, immediately flush out the entire system and use the correct DOT rating-based brake fluid recommended by your car manufacturer.

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