Castrol SRF VS Motul 660: Which One Is The Best Brake Fluid

Thinking of switching your brake fluid? Well, we know how confusing and worrying it can be. Because it’s directly connected to your safety. 

So, which brake fluid should you choose between Castrol srf vs Motul 660?

Well, Castrol SRF is one of the best brake fluids in the market. The wet boiling point of this brake fluid is second to none. It doesn’t need to be changed too often which makes it more price efficient. But, if your vehicle is for racing purposes only, Motul 660 can be your pick.

This is just the summary of the whole discussion. You should get a better idea about this before making a decision. 

So, let’s head into the detailed comparison between them!

Motul 660 VS Castrol SRF: The Basics

The hydraulic fluid we use in our brakes is called “Brake Fluid”. Haven’t you always wondered how pressing the pedal makes the car stop?

Well, the force applied on the pedal is transferred by brake fluid to the pads. So, you can say it works as the “Mediator” or “Middle Man”. 

Now, Castrol SRF and Motul 660 are two most common brake fluids in the market. 

So, it’s common to wonder which is the best fluid. But it’s better to know the differences between them and choose accordingly. 

Thus, we have made a brief table to make their comparison easier-

FeaturesCastrol SRFMotul 660
Wet Boiling Point518°F or 270°C399°F or 204°C
Dry Boiling Point590°F or 310°C617°F or 325°C
Changing FrequencyLessMore

Castrol SRF VS Motul 660- Head To Head Comparison

Now, you have a brief idea about the two brake fluids. But it’s time to head into the detailed comparison. We’ve broken down each category and tried to explain it easily-

Wet Boiling Point

The wet boiling point is an important parameter of brake fluid. It’s the temperature at which brake fluid boils after absorbing 3.7% water. A higher value of this will mean better longevity of the brake fluid.

We can see a huge difference in this category between the two brake fluids. Castrol SRF has a very high ceiling at 518°F or 270°C. In contrast, the Motul 660’s wet boiling temperature is at 399°F or 204°C.

Anyhow, flushing your brake frequently makes the wet boiling point irrelevant.

Winner: In general, it’s better to use Castrol SRF. But, if you are a hard driver, any of these two oils will be fine.

Dry Boiling Point

The dry boiling point of brake fluid is a super important aspect for racers. It is the boiling temperature of brake fluid when it’s new, fresh, and unopened. It refers to the highest temperature, at which the oil won’t disintegrate.

So, the higher the dry boiling temperature, the better. As a matter of fact, Motul 660 has the highest dry boiling temperature. Castrol SRF isn’t far off from that standard as well. It has a dry boiling temperature of 590°F or 310°C.

Winner: If you are considering the dry boiling point, Motul 660 simply is the best. So, it’s better to use Motul 660 based on this category.

Changing Frequency

Changing frequency is how frequently you flush your brake fluid. It normally depends on which purpose you use your car for.

Now, you might be using your car on the race tracks. In that case, using Motul 660 can be costly. As you need to flush it after every event. It has a lower wet boiling point making it less durable.

On the other hand, Castrol SRF has a better-wet boiling point. Thus, making it more durable. It doesn’t need changing as often as you need while using Motul 660. You can change your brake fluid twice every season. 

But, in both cases, if you use them in the street, it’s totally fine.

Winner: It is clear that Castrol SRF is the better one. The reduction in changing frequency also plays a vital part in cost reduction.

Price Point

Price always plays a big impact in our decision-making while buying something. But, it’s never a bad decision to spend some extra on a better product.

Castrol SRF is a bit pricey at 74.5$ a litre. On the other hand, Motul 660 costs much less. The price is 54$ per litre. So, you must be thinking, Motul 660 is the one to go with.

But, you have to keep the changing frequency in mind. As we’ve discussed, Motul 660 will need to be changed more frequently. Therefore, this makes Motul 660 more expensive than Castrol SRF.

Winner: According to your purpose the winner in this category changes. If you want to race, then Castrol SRF is the way to go. Otherwise, go for Motul 660.

Can I Use Motul 660 Instead of Castrol Srf and Vice Versa?

Both of these brake fluids will give you great performance and safety. As you can see, Castrol SRF stands out in almost every category. So, It’s better to use this brake fluid in your vehicle. 

Motul 660 is slightly cheaper than Castrol SRF. But Castrol SRF will charge less because you won’t need to change it frequently. 

But if you’re not worried about price and you race frequently, go for Motul 660. It has a higher dry boiling temperature, giving it the edge between them. 

Can I Mix Castrol Srf and Motul 660?

We suggest against that. They have different boiling temperatures. This means they will have difficulties while merging. This will result in your car’s brakes not working properly. So, going with only one is the right choice!


Question: How much brake fluid is needed to bleed the brakes?

Answer: On a single set of cycle brakes, 50ml brake fluid is enough. This amount may increase if your old brake fuel is discolored. You will need to completely drain the old fluid and replace it.

Question: Which brake fluid should I use in my brakes?

Answer: You should use brake fluid according to your brake model. This is normally printed on the lever assembly or reservoir top cap.

Question: How does moisture get into the braking system?

Answer: The brake fluid is hygroscopic in nature. Meaning it absorbs moisture from the environment. This moisture can come through microscopic pores in hydraulic lines.

Ending Note

So, that was all about Castrol srf vs Motul 660. Hope we could help you to take this important decision.

See you next time with something else.

Until then, be safe while driving or racing!

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