Does Brake Fluid Circulate?

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Brake fluid circulation is a matter which has steered a lot of argument, especially amongst those who love to speak from the background of physics. While there are theories and laws for and against brake fluid circulation, this article aims to clear up this misconception.

So, does brake fluid circulate? A simple yes or no may not do justice to this question given the amount of interest in this. However, there can only be one answer to this and that is brake fluid does not circulate. It is not however as simple as that, and here is why.

Even though most of this article goes on to explain why brake fluid does not circulate and how to confirm this, the circulation mentioned here is also to be differentiated from diffusion.

The amount of water seen in the brake fluid sample taken from the reservoir cylinder will most likely be the same as the brake fluid sample from the master cylinder or brake lines. This is because both the moisture and brake fluid are two miscible fluids and obey certain laws of diffusion.

Some may insist on circulation, believing this to be necessary for the transmission of force necessary to bring the car to a halt. However, this is not needed in the working mechanism of the brake fluid. 

A good way to understand the brake system is to see it as the nerve conduction process in the human body. The movement of the hand or any other part of the body is orchestrated by muscles, that is, the flexor and extensor muscles. 

However, there are a lot of processes that went on before the eventual movement of the limb, starting with the nerve impulse from the brain. The impulse is conducted through a series of interconnected axons which eventually link up with the muscles targeted for the message.

Similarly, when the brake pedals are pressed, parts such as the piston, brake fluid, brake line, calipers, rotors, brake pads, and others that are all interconnected work to see that the rotational motion of the wheel is slowed down or brought to a stop.

This is achieved via transmission of force through the brake fluid, which in this instance acts like a solid material, until the force gets to the calipers, and compresses the pads against the rotors, to create traction in the car.

This question is not only asked by the physics nerd, rather, it’s also a debatable topic amongst those intending to only swap the brake fluid in the reservoir cylinder and not bleed out the entering fluid. Here, you will learn why such practice jeopardizes your brake efficiency.

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Can you change the reservoir brake fluid alone?

It is hard to escape the advice about changing the brake fluid. This will often come from the guy at the maintenance shop who may or may not be an expert. Rather than assuming you know better or believing it’s a way of getting you to spend a few dollars, listen to the experts on this one.

Each time you step on the pedal or drive your car, the brake fluid suffers an enormous heat insult. The heat from the pads finds its way into the fluid and on some occasion cause the fluid to boil especially when the water content of the brake fluid is at a substantial level.

Now, I can start by reminding you of the adage which says “ whatever is worth doing is worth doing well. I hope that is how the adage is said. Anyway, the issue of refilling the brake fluid is much more serious than that. So, if you decide to only replace the reservoir brake fluid, then you have failed to understand how serious this is.

It is a mistake to consider the brake fluid in the reservoir as the state of the entire brake fluid. Have you ever seen fruits such as mangos or garden eggs appearing healthy externally and yet the inside is filled with worms and eggs from such worms?

This sometimes is the deception caused by the brake fluid in the reservoir cylinder because it suffers less insult. The brake fluid in the lines may have gas bubbles while the portion in the reservoir cylinder may still look okay at the same time.

Therefore, when you decide to swap only the fluid in the reservoir cylinder, you may have left out the portion of the brake fluid that needs to be replaced the most.

How often should you bleed the entire brake fluid?

The frequency of brake fluid flushing and refilling can be left to the discretion of the car owners. Most people maintain 3 monthly schedules or have this done every summer depending on maintenance practice.

The lifespan of the brake fluid is not really about the expiry date, rather, it is about the number of heat cycles as well as the moisture content of the brake fluid. These two factors impact the chemical composition of the fluid which in turn affects the brake’s pH, corrosiveness, and other properties.

So, aside from the expiration date, estimation of the lifespan of the brake fluid includes the type of vehicle, driving frequency, road condition, driving style, braking style, and maintenance practices amongst others.

On average, off-track cars can make use of the same brake fluid for a couple of years. This is safe if only the user has the fluid tested every once in a while for water, copper, and other determinants of contamination.

What contributes to the reluctance seen with most persons in respect to prompt replacement of the brake fluid with new fresh fluid is because you are unable to see for yourself the nature of the brake fluid in the brake lines. 

What will happen if you fail to bleed the brake fluid?

The physical properties of the brake fluid can be seen to change drastically when the brake fluid goes bad. The accumulating dirt, color change, change in pH, and increase in copper level amongst other chemical and physical changes is why you are being advised by all car professionals to take this matter seriously.

If the brake fluid was contained so that all portions can be seen and not only the portion in the reservoir cylinder, most people would appreciate better how different the current state of the fluid is from when it was poured in a couple of years ago.

With a couple of dollars, you can get new brake fluid and change it yourself if you can follow simple instructions. It only takes a few steps to have the brake fluid bleed out using a power or vacuum bleeder. The new brake fluid is simply poured in.

However, following the determination of the deteriorating state of the brake fluid, failure to change the fluid and continuous driving of the vehicle will lead to damaging effects on the calipers and other brake parts which will eventually cost more than what would have been spent on the brake fluid alone.

There are many ways you can decide to go about this process. The easiest and most common is to have an expert take a look especially if you do not want to have your hands dirty. However, can this be done by yourself without having to go to the auto shop? The answer is yes!

You can choose to bleed out the brake fluid without assistance from a vacuum or power bleeder if you do not have any of these. You can rely on gravity to help pull out the fluid. This however may take more time than when using bleeders.

Efficient flushing is emphasized when intending to stop the use of a certain type of brake fluid such as the glycol base and switch over to the silicone base.

Most of the argument about the circulation of brake fluid is only backed by physics theories without practicality. Rather than dwelling on proving whether the brake fluid circulates or not, endeavor to carry out a regular change of the fluid, do this properly and you will not have to worry about signs of a failing brake system.

How will you know when the brake fluid needs to be bled out and changed?

How long a brake fluid last is equally up for debate. The brake fluid, the tools needed to change the fluid, and the workmanship cost for changing the fluid does not cost much. There is therefore no sane reason for anyone to refuse to change the brake fluid when it is due for a change.

However, if the fluid is not changed, it is only a matter of time before you begin to experience the pedal sinking and not returning promptly after being pressed. This may cause the brake lights to remain turned on even when the foot is not on the pedal.

Aside from this, you may also have to deal with, smell, and noise from the brake system, plus the fact that you cannot drive with peace of mind knowing that the brakes cannot be trusted.

Does Brake Fluid Circulate – Conclusion

As for diffusion, there are laws and theories as well as for this. However, the brake fluid has not been demonstrated to circulate and should bleed out entirely when due for a change.

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