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Motul 660 Vs Castrol SRF: Which Brand Is Better?

With so many available options, settling on a single brake fluid can be challenging. Castrol SRF consistently outperforms the competition, but many people prefer to use less expensive braking fluids because of their high cost. Therefore, Motul 660 will be your best option if you’re looking for the best budget fluid.

I think the type of fluid you use should depend on your driving style, vehicle weight, horsepower, and more. First, before making any final selections, let’s look at how Motul 660 and Castrol SRF, two of the most common braking fluids used on track days, compare in terms of their technical specifications.

Motul 660 vs. Castrol SRF: Which Brand Is Better?

This section will focus on an in-depth discussion of two different brands. In this article, I will try to briefly overview both categories by dividing them into their component elements.

Motul 660 Vs Castrol SRF

Moist Boiling Point

This is a characteristic of all braking fluids. This is the point at which brake fluid will boil after absorbing 3.7 percent water. Brake fluids with a better quality rating tend to last longer.

When heated to 270 degrees Celsius (518 degrees Fahrenheit), Castrol SRF is at a higher temperature than Motul 660, which is set at 204 degrees Celsius (399 degrees Fahrenheit). However, if the brake is flushed regularly, this wet boiling point is a moot matter.

When it comes to regular driving, Castrol SRF is a good option for brake fluid. However, both of these oils are suitable for the most demanding drivers.

  • Changing Frequency

The term “changing frequency” refers to the frequency you should cleanse your braking fluid. With a lower wet boiling point, it’s more dependable. Using Motul 660 fluid will require two changes every season.  

Compared to Motul 660, Castrol SRF is superior. This less frequent replacement is a significant factor in lowering expenses.

  • Waterless Boiling Point

The waterless boiling point is a vital attribute for racers. It is the temperature of fresh, exposed brake fluid. Oil can usually withstand temperatures up to this point before melting. As a result, the maximum feasible temperature for dry-oiling is achievable.

However, Motul 660, in this instance, has a very high waterless boiling temperature. C Castrol SRF complies with this requirement, having a temperature of 310 °C (590 °F). Thus, Motul 660, which has a higher boiling point, is the best braking fluid to use with them.

  • Price Point

Spending a little more money to ensure you have the best possible product is not always a bad idea. Comparatively, Castrol SRF costs 74.5$ for one liter, and Motul 660 costs 54$ for one liter.

Knowing the price, you’ve probably decided that Motul 660 is your best bet. Before making a decision, think about whether or not you’d be open to varying the frequency. 

Earlier in the discussions, it was mentioned that Motul 660 brake fluid needs to be replaced more frequently than Castrol brake fluid. Thus, Motul 660 brake fluid costs more than Castrol SRF.

Motul 660 vs Castrol SRF- A quick comparison

  Brand  Motul 660  Castrol SRF
Product Dimensions3.3 x 7.25 x 2.15 inches11.02 x 7.19 x 3.24 inches
Liquid Volume500 Milliliters1 Liter
Car typeCar, MotorcycleRacing car
Item Weight1.28 pounds2.02 pounds
PerformanceSuperior aerodynamic performanceHigh-performance
Dry boiling point312 °C310 °C
Wet Boiling Point205 °C269 °C
Price Range$54.85$74.95

Motul 660 Wins

Let’s take a close look at this specific part to gain more about

the advantages of Motul 600 brake fluid.

Effective Even When It Rains

Since the non-silicone base fluid has a wide variety of wet boiling points (from high to comparatively low) and a typical Dot of 5.1, it aids in breaking due to rain. Brake fluids can always find in atmospheric moisture. Besides increasing the likelihood of vapor lock, it can also induce the boiling point to drop. 

Therefore, the wet boiling point is determined by including an additional 3.5% humidity in the air. The air vents’ wet boiling point is slightly more relevant, but both attributes can lower it.

  • The Highest Possible Temperature Stability and Resistance

Motul 660 brake fluid provides excellent performance in racing scenarios. It works as intended in braking systems even when subjected to extreme heat. As a result of its high resistance to heat and high durability, it helps boost overall performance. Furthermore, it can help make a solid brake even in the worst conditions.

  • Withstands Extreme Temperature

The whole structure of Motul RBF 660 is synthetic, in contrast to conventional brake fluids. This brake fluid can be used in any hydraulic clutch or brake system, regardless of whether it requires a silicone-based or non-silicone fluid. 

Moreover, Motul dot-4 is a fully synthetic brake fluid designed for racing that offers superior heat resistance. Further, these fluids are compatible with standard clutch systems and steel rotors.

Motul 660 Losses

Do not mix this brake fluid with polyglycol-containing fluids since the combined fluids will perform poorly. You can rectify this error by purchasing this item in bulk. However, it would be best if you didn’t mix this with brake fluids that include silicone or mineral oils. If you use Motul 660 fluids, they can degrade the fluid’s quality and performance.

Castrol SRF Wins

When it comes to “performance” braking fluid, Castrol SRF is your best bet. The benefits of Castrol SRF are outlined below.

  • High-Performance  Brake Fluid

Castrol SRF is on par with DOT 3 and DOT 4 brake fluids in terms of compressibility. This means that whenever mineral oil is called for, such as in brake and drum systems, Castrol can use with no problems.

Once this brake fluid is used, the brake pedal will feel “firm.” This outstanding Castrol product is patented in several countries for its superiority. They are particularly notable for exceeding JIS K2233, FMVSS 116 Dot 4 and Dot 3 criteria, and other US Federal laws.

  • High  Dry Boiling Point

Due to its high dry boiling point, SRF brake fluid is best used in challenging braking scenarios, such as racing. This feature can surpass the boiling point requirements for dot-5 fluids.

In road vehicles, SRF brake fluids provide a higher stopping force because they can withstand severe driving after a year or two of storage at 3.7 percent humidity.

  • High-Vapor Lock Point

There are additional advantages to using Castrol, such as its high vapor lock point and long service life. However, this brake fluid is suitable for use in any braking system that does not use mineral oil.

Castrol Losses

The consequences of using Castrol SRF brake fluid are listed


  • Costly

Castrol SRF costs a lot more than competing braking fluids. Although it is one of the most expensive braking fluids available, it is also one of the most frequently utilized. 

Mixing Castrol SRF with ordinary brake fluid can reduce the effectiveness of the Castrol SRF. Due to this, before replacing the old brake fluid with Castrol SRF, make sure to flush out the system completely.

Final Verdict

Regarding the above, I have done my best to provide as accurate and helpful information about Motul 660 vs. Castrol SRF as possible. This article will provide the details you have to make a wise choice. Castrol SRF and Motul RBF 660 are top-tier brake fluids that deliver excellent results.

As this article illustrates, Castrol SRF is the top fluid and the clear victor. This fluid, while notable, comes at a high price, yet it performs admirably even in the harshest environments. That’s why this fluid is such a good option for improving performance.

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