Brake fluid is an essential part of your car’s braking system, and keeping it in good condition is vital to maintaining vehicle safety and performance. Below, we explain what brake fluid is, how to maintain it, and how often it should be changed.
What is brake fluid?
Brake fluid is the liquid contained within hydraulic braking systems that transforms the force of you pressing down on the brake pedal into pressure which then forces the brake pads to squeeze the discs. On top of this, brake fluid also lubricates the braking system and helps to prevent issues with corrosion, which can have a big impact on the braking capability of your vehicle.
Unfortunately, the heat generated by the friction between the brake discs and the brake pads can cause water vapour to form and then condense within the brake fluid. This prevents it from working as well as it usually would by lowering the temperature at which the fluid boils. The braking function can also be affected by the fluid level being too low, which is why it’s important to regularly check the brake fluid.
How to top up brake fluid
In order to keep on top of your vehicle maintenance and avoid problems, it’s a good idea to check your brake fluid on a routine basis – every three or four months should be appropriate. Lots of car dashboards have a symbol that lights up to tell you when the fluid level is low, but as we’ve mentioned, this isn’t the only issue that can occur. Make sure to check the brake fluid when you notice the warning light, but don’t let that be the only time you do so. So how do you go about checking and – if needed – topping up your brake fluid?
- Step 1 – Perform a short test drive
A short drive around the block, remembering to test the brakes several times, helps to fill the braking system with fluid. This makes it easier for you to get an accurate reading when you check the level. It can also flag up any issues with your brakes, such as squeaking brakes, the car pulling to either side, or the vehicle not slowing as quickly as you’d expect. - Step 2 – Park somewhere level
In order to check the level of your brake fluid, you’ll need to park somewhere flat. If you park on a hill, even a slight one, this will affect the reading, so opt for a level area. If you don’t usually park on the flat, try a car park – these are usually level. - Step 3 – Locate and check the brake fluid reservoir
Once you’re parked up, open the bonnet and find your brake fluid reservoir. It should be a white container with a yellowish-brown fluid visible inside and minimum and maximum markers on the side – as pictured at the top of the page. If you’re struggling to find it for any reason, there should be a diagram in your vehicle’s manual that locates it for you.
If the brake fluid is somewhere between the minimum and maximum markers, you don’t need to do anything – although if it is close to minimum you should probably top it up anyway. If the level is below the minimum, add some brake fluid, being careful not to fill it past the maximum. If the level is already past the maximum, this could be a sign there is water in the system. You’ll need to have the brake fluid changed at your local Mr Clutch Autocentre to avoid braking faults.
It’s also important to have a look at the brake fluid inside the reservoir, even if you’re not going to top it up. If the fluid looks very dark, has bits floating in it, or seems thick, that’s a good indicator your brake fluid needs to be flushed out and replaced.
What brake fluid do I need?
There are two types of brake fluid typically used in non-commercial vehicles, and these are known as DOT 3 and DOT 4. The ‘DOT’ part stands for Department of Transportation, which is responsible for the categorisation of brake fluids. Both DOT 3 and DOT 4 brake fluids are poly glycol-based, with a moisture absorption rate of 2% per year. This means that in the space of a year, the fluid will absorb 2% of its volume in water.
So what makes them different? Well, DOT 3 can be thought of as your standard brake fluid to be used in the majority of cars driven primarily within a certain altitude of sea level. It has a wet boiling point of 140°C. DOT 4, on the other hand, has a higher boiling point of 155°C, and is designed for use at higher altitudes.
When it’s time to change your brake fluid or top it up, check your vehicle’s manual to find out which type of brake fluid is recommended for use in your car. You can also ask a mechanic for their expert opinion if you’re not sure.
How often to change brake fluid
It’s recommended that you change your brake fluid at least every two years, as it’s a vital part of the braking system. However, in practice it’s likely that it will need to be replaced before then, so it’s important to regularly check the brake fluid to make sure it’s in good condition. Your brake fluid needs to be replaced if:
- It’s very dark
- It looks thick
- It smells different to usual
- You can see debris floating in the liquid
- It fails a boiling point test – i.e. it boils at too low a temperature
Brake fluid checks are included as part of a car service. This involves checking the boiling point of the fluid (to determine whether it’s contaminated with water) and assessing the fluid’s colour and appearance. Regular car servicing can help to ensure your brake fluid is replaced promptly before further damage is done, keeping you and other cars safe on the road.