From the moment that brake fluid is removed from a sealed container and put into your car, it begins to absorb moisture from the air. These quantities are very small to begin with, but over time the amount of water which can be taken into the fluid is staggeringly high. Every time that the master cylinder is opened, air and moisture can enter the reservoir and be absorbed by the fluid itself. This is why the cylinders are usually transparent, so that you can check the level of brake fluid in your car without having to open the reservoir and compromise the quality of the brake fluid.
Water doesn’t sound like it should be a dangerous substance to be trapped inside your car, but when mixed with the brake fluid, it can seriously reduce the boiling temperature of the fluid. In vehicles with many moving parts which generate a lot of heat, brake fluid needs to be able to retain its high boiling point, otherwise it could become extremely dangerous.
In the UK, with a climate which includes a lot of rain and humid air, replacing your brake fluid on a regular basis is even more important. Tiny pores within the brake hoses and the slightest of gaps on the bleeding valves regularly allow water and moisture to enter the brake fluid in our cars without us having any idea that it is happening.
Contamination of the brake fluid is not the only problem you need to look out for. For various reasons throughout your car’s lifetime, brake fluid levels may change. If there are gaps in the fluid hoses where moisture can get in, then it is reasonable to assume that some of the brake fluid could also leak out. It couldn’t be easier to check the level of fluid in your vehicle.
Your owners’ manual will give you a detailed diagram of exactly where the master cylinder is in your car and once you open the bonnet, you should be able to spot it fairly easily. There will be a line marked on the cylinder which shows where the brake fluid level should come up to. If the level is significantly lower than this line, then you need to do something about it, fast. It is easy to top up fluid levels, but the logic shows that if the brake fluid can get out, moisture and impurities can also get in.
If you find that your brake fluid levels are low then it will be worth taking your vehicle for a brake and hydraulics service, to replace the brake fluid completely, rather than just topping up the contaminated fluid which is already there. The brakes are your lifeline when driving. It is not worth taking the risk of compromising their effectiveness.
