Can You Mix Synthetic Brake Fluid With Regular Brake Fluid?

We all know that brake fluid is essential to all hydraulic braking systems. You must ensure the braking system works as designed. It doesn’t matter whether you’re a spirited or regular driver. We all need brake fluids in hydraulic braking systems.

The question is, can you mix synthetic brake fluid with non-synthetic brake fluid? Can you use one in place of the other? This article will provide all the answers you need. But first, let’s see what synthetic brake fluid is.

can you mix dot 4 and dot 4 synthetic brake fluid

What is Synthetic Brake Fluid?

Synthetic brake fluid is made from the same base stock as its conventional counterparts. They all contain polyethylene glycol stock. When producing synthetic brake fluids, the producer will synthesize the base stock to make the molecules more consistent and better than the conventional ones.

The manufacturers typically add other molecules to improve the fluid performance. Synthetic brake fluid manufacturers use different additives in formulating their fluid. The addictive package includes anti-foaming, anti-corrosion, and other additional additives that offer the desired fluid characteristics.

Simply put, synthetic brake fluid is a mixture of base stock, tetraethylene glycol monoalkyl ethers, along with di-, tri-. They contain compounds that reduce oxidation at high temperatures and prevent corrosion.

Recommended vehicle to use synthetic brake fluid

It is best to consult your vehicle owner’s booklet to see the recommended brake fluid. If the manufacturer recommends a DOT 3 or DOT 4 brake fluid, I can use either regular or synthetic brake fluid that has the same DOT rating.

Also, if your car manufacturers recommend DOT 5, stick to the DOT 5 brake fluid.

Here’s the thing, brake fluid producers can formulate synthetic brake fluid to meet either DOT 3 or DOT 4 requirements. Synthetic refers to the compositions and performance characteristics rather than the DOT rating.

Pros of synthetic brake fluid

Synthetic fluid has advantages over non-synthetic brake fluids. The benefits of synthetic brake fluid over regular fluid include the prevention of rust build-ups, better lubrication abilities, lasting longer, being compatible with rubber components, and working better against corrosion.

Prevents build-ups: Synthetic brake fluid does not leave residues behind. In other words, it keeps the brake lines clean, which helps for optimal braking experience.

Prevents corrosion: Synthetic brake fluid provides a slim coating layer for the brake lines. It also prevents any particles, dirt, or grime from corroding the metal brake parts.

Better lubricating abilities: One of the crucial benefits of synthetic fluid is that it provides better lubricating abilities. It means that it provides extra protection to the brake parts, making them last longer.

Works better with rubber parts: Most brake system components use rubber seals to prevent fluid leaks. Over time, these seals start wearing out, leading to brake leaks. But with synthetic brake fluid, you don’t have to worry about replacing rubber seals often.

Also, you can rest assured that a leaking fluid will not cause any damage to the brake system components.

Last longer: Theoretically, synthetic brake fluid lasts longer than non-synthetic brake fluids. Yes, synthetic brake fluids do not pose any harm to rubber parts and prevent corrosion and build-ups. Another essential reason to switch to a synthetic brake fluid is that it lasts longer.


There are always merits and demerits to everything on earth. Synthetic brake fluid is no exception. The most common demerits of synthetic brake fluid are their cost and availability.

Cost: Generally, synthetic brake fluid is costlier than their regular counterparts. If you are on a budget, you may not want to spend that extra dollar on synthetic brake fluid.

Availability: Synthetic brake fluids are not widely available in some remote areas. So, if you live in a remote location, synthetic brake fluid may not be available there. Of course, this may prompt you to mix synthetic brake fluid and regular or use regular instead of synthetic fluid.

What is regular brake fluid?

Regular brake fluid is the most common type of fluids used in hydraulic braking systems. They are typically glycol-ether-based and has lower boiling points than most synthetic brake fluids. They can also absorb water from the air.

All regular brake fluids are either rated DOT3, DOT4, or DOT5.1. However, some synthetic brake fluids can be DOT5.1, DOT4, or DOT3.

Pros of regular brake fluid

Like synthetic brake fluid, regular brake fluid has its pros and cons. Here are the pros of DOT 4, DOT 3, and DOT 5.1 conventional brake fluids.

Wide availability: Regular brake fluids have been in existence since the inception of hydraulic braking systems. They are still needed in today’s vehicles. As a result, they are widely available in various automotive repair centers, online, and local retail shops.

Cost-effective: They are more affordable since they do not require additional additives in formulating them, making them affordable for everyday driver.

Common standard: Regular brake fluids meet industry standards sets by the Department of Transportation (DOT). Conventional brake fluids are typically DOT 5.1, DOT 4, and DOT 3. These standards ensure compatibility and consistency across all vehicles. However, most synthetic brake fluid follows this same industry standard.

Compatibility: Like synthetic fluids, regular brake fluids are compatible with various vehicle components. They do not deteriorate or cause damage to rubber seals, calipers, and brake pots.


Regular brake fluids have their cons. They include hygroscopicity, corrosive properties, and compatibility issues with silicone-based fluids.

Hygroscopicity: DOT 3, DOT 5.1, and DOT 4 non-synthetic brake fluids are hygroscopic. It means that regular brake fluids can absorb moisture over time. If this happens, there will be a vapor lock or reduced braking performance. It can also cause the fluid to degrade and require earlier replacement.

Regular replacement: As explained earlier, regular brake fluid absorbs moisture over time, which leads to degradation. Hence, the fluids need to be replaced regularly to maintain optimal performance. However, the replacement interval varies, depending on the manufacturer’s recommendation for your car. Most manufacturers recommend replacing regular brake fluid every two years.

Corrosive properties: Some regular brake fluids have some corrosive properties. The glycol ethers in conventional brake fluid contain corrosive properties. These corrosive properties can damage brake components.

Additionally, all regular brake fluids, such as DOT 3 and DOT 4, can eat away car paint. So, when working with regular brake fluids, handle it with diligence to avoid stripping off your car paint.

What’s the Difference Between Regular Brake Fluid and Synthetic Brake Fluid?

When looking at synthetic brake fluid or regular brake fluid, we concentrate at the compounds used in formulating them. It has nothing to do with the DOT rating.

Both synthetic and regular brake fluids are made with the same materials. Do not mistake synthetic brake fluid for only DOT 5. DOT 3, DOT 4, and DOT 5.1 can be regular or synthetic brake fluid.

DOT 5 synthetic fluids are made of silicone-based compounds, while conventional brake fluids are made from mineral oils. The mineral oils are extracted from petroleum products.

Regular brake fluids can absorb moisture from the air. This means their boiling point will decrease over time. On the other hand, synthetic brake fluids are not hygroscopic, meaning they do not absorb moisture from. This allows synthetic fluids to maintain a stable boiling point.

Another prominent difference between regular and synthetic brake fluids is how they are refined. Synthetic brake fluids are refined more to make them more consistent and reliable.

DOT 5 is a silicone-based brake fluid, and they are not recommended for older vehicles. As a result, manufacturers now produce synthetic fluids with the same mineral oils used for regular fluids, making it possible for old vehicles to use synthetic brake fluids.

The only difference between DOT 5.1, DOT 4, and DOT 3 synthetic brake fluid is the additives used in formulating them. They have the same base material. But DOT 5 synthetic brake fluid is way different from other DOT ratings, whether regular or synthetic.

Can you mix synthetic brake fluid with regular brake fluid?

Brake fluids can be either mineral or synthetic. You can mix them without issues, provided they are rated DOT 3, DOT 4, or DOT 5.1. Both regular and synthetic brake fluids are miscible.

So, if you are asking, can you mix synthetic DOT 3 brake fluid with regular DOT brake fluid? Yes, you can mix them without any issues.

However, you can not mix synthetic and regular brake fluid if any of them is rated DOT 5. DOT 5 brake fluids are silicone-based and incompatible with other fluids with different DOT ratings.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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