Can I Use Motor Oil As Brake Fluid

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When it comes to oil and fluid replacement, you may think you can use motor oil as brake fluid or vice versa. Although these two types of products are used for different purposes, they have similar properties.

These two products have different viscosity, additives, and boiling points. A motor vehicle’s engine and braking system are crucial safety parts. If you use the wrong oil or fluid in your car, you risk your life and money.

This post will discuss the difference between brake fluid and engine oil. Can you use engine oil as a brake fluid?

Engine oil refilling

What is brake fluid?

Brake oil is a hydraulic fluid used to transfer force into pressure to stop or slow down a car, and it is also used in small vehicles and light trucks. Brake fluid has a higher viscosity, and it’s used to transfer force into pressure. High viscosity means it resists flowing and sticking to surfaces, making applying pressure to the brake pads easier. These fluids are made of Ethylene Glycol-based fluids.

Brake fluids are synthetic with manufacturers’ added additives that improve performance and help prevent squeaks and other noises from being made while the car is braking. You have to change the brake fluid periodically, and these fluids generally include Oxidation Inhibitors, Corrosion inhibitors, modifier couplers, solvent diluents, and lubricant additives.

There are mainly three types of brake fluids on the market.

  • DOT 3: This is the most common brake fluid on many cars and trucks’ hydraulic brake systems. It is a Glycol Ether base. Compared with other products, this has a lower boiling point. It is a fully synthetic fluid without silicone-based. DOT 3 is hygroscopic, which means it absorbs water. Therefore, it has a short life and can quickly become contaminated by absorbing moisture if the fluid is exposed to air.
  • DOT 4: This product is similar to DOT 3 but has a higher wet & dry boiling point. It is made of glycol-based fluids, making it more efficient and suitable for high braking temperature vehicles. DOT 4 is a fully synthetic-based fluid without silicon. This fluid absorbs less moisture so it can be used more extensively than DOT3, but you should not expose the fluid to air. All the DOT 3 compatible cars and trucks can use DOT 4.
  • DOT 5: This product is made from silicon and has a higher boiling point than DOT3 and DOT4. This fluid is non-hygroscopic, which means it does not absorb moisture from the air. Silicon-based brake fluid is ideal for vehicles that operate in extreme temperatures (too low temperatures).
  • DOT 5.1: This brake fluid mixes glycol-based, borate ester, and silicone. It is a synthetic fluid, and it has the highest boiling point. DOT 5.1 is compatible with DOT 3 and DOT 4 but not compatible with DOT 5. This brake fluid can absorb moisture from the air, but even after absorbing water, it can be used for an extended period.


Brake Fluid Specification

Type Dry Boil PointWet Boil PointCompositionMixable
DOT 3401°F/205°C284°F/140°CGlycol EtherYes
DOT 4446°F/230°C311°F/155°CGlycol Ether/Borate EsterYes
DOT 5500°F/260°C356°F/180°CSiliconeNo
DOT 5.1500°F/260°C356°F/180°CGlycol Ether/Borate EsterYes


What are brake fluid’s wet and dry boiling fluids?

The boiling point of a pure fluid without water or other contaminants is known as its dry boiling point. The wet boiling point is the boiling point of a fluid containing water.


What is engine oil?

Engine oil (motor oil) is a lubricant used to reduce friction and wear of internal combustion engines. It helps to keep the engine running smoothly and prevents it from overheating. There are several reasons for using engine oil: Lubrication, Cooling, Protection against corrosion, and Sealing engine parts. This will ensure a long lifespan, good running engine, improve gas mileage, and reduce emissions.

Engine oils come mainly with two types of viscosity: single grade and multigrade. Overall there are over 11 viscosity ratings for engine oils. Motor oil has a higher boiling point.

There are mainly three types of motor oils in the market.

  • Mineral engine oils.
  • Semi-synthetic engine oils.
  • Synthetic engine oils.


Periodically we have to replace the engine oil, and we cannot mix different types of motor oils.


Can you use motor oil instead of brake fluid?

The simple answer is you should not use engine oil as brake fluid. These two products have different viscosity and different base oil and additives. These two products are exclusively developed for different purposes. The braking system is a hydraulic system, and motor oil is not developed for use in a hydraulic system. Using motor oil in the braking system will deform and damage brake system seals. It will result reduce the pressure on the braking system. Therefore, you should not put oil in the brake fluid reservoir.

The in-depth answer to this question is complex and depends on several factors. Brake oil is specifically designed for brake systems, while engine oil is used as a lubricant in various engines. The hydraulic braking system has a master cylinder and wheel cylinders. They have several pistons. Contaminated or using incorrect viscosity fluid can damage or deform the piston seals. This will result in bleeding fluids.

Furthermore, the caliber assembly has a rubber seal, and if you use the wrong fluid, this square-cut seal deform and can reduce the caliber pressure and leak fluids to other chambers. Furthermore, if your vehicle has an anti-lock braking system, it can damage its pistons if you use the wrong brake fluid. This will ultimately reduce the braking system pressure, and it can result in braking failure.

Braking fluid damage seals



What are the differences between brake and engine oil?

Brake oil and engine oil have different viscosity ranges, and these two products are developed for different purposes. Brake oil is used on brakes to help reduce friction and stop the car. It’s made of various compounds, including anti-freeze, which helps keep the fluid from freezing. Engine oil is used in engines to lubricate and protect parts and keep them running smoothly. It contains additives and metals like copper and zinc to help prevent wear and tear on your engine parts.


Is brake oil and engine oil same?

Brake oil and engine oil are not the same and cannot be interchangeable. Brake oil is a type of lubricant used in braking systems, while engine oil lubricates engine parts and reduces friction. Brake oil and engine oil are both lubricants that prevent friction and wear on moving parts. However, there are several significant differences between the two products. Brake fluid is used to stop or retard the movement of the brake system, while engine oil is used to reduce engine metal parts’ friction and wear.



You must replace your vehicle oil and fluid when scheduling car maintenance. Brake fluid transfers pressor in a hydraulic braking system, while engine oil is used to lubricate and protect the engine. Brake oil comes in different types, depending on your car type (eg, DOT3, DOT4, DOT5, and DOT5.1). Engine oil can also be divided into mineral, synthetic and semi-synthetic.

Overall, brake oil and engine oil are different types of lubricants that are used for different purposes. However, they both have essential functions in a car. Engine oil cannot use for the braking systems, and braking fluid cannot use as engine oil. When motor oil flows into the braking system, it can damage and deform hoses, squire cuts, lip seals, and plungers.

Here are a few more details about each type of oil:

  • Brake Oil: Brake fluid is a hydraulic fluid specifically designed for brake systems, and it’s made up of Glycol Ether or a combination of  Glycol Ether and Borate Ester with additives. This fluid help reduce friction and wear in the braking system.
  • Engine Oil: Engine oil is a lubricant that is used in a variety of engines. It helps reduce heat build-up and prolongs the life of your car’s engine. It has a different viscosity range and is made of mineral or synthetic base oil.

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