When to Change Brake Fluid?

When should you change your Brake Fluid?

Performing a similar role to that of a bicycle cable, brake fluid connects a car's pedal to the brakes. While the fluid within car braking systems cannot snap, it can still fail. As brakes convert motion to heat, the fluid gets hot. While conventional new brake fluid boils at around 275 degrees Celsius, its ability to absorb heat energy reduces as the fluid ages.

Why do I need to change my brake fluid?

Unfortunately, the fluid sucks moisture from the surrounding air. You cannot prevent moisture from sullying the fluid, because it enters through the semi-permeable flexible rubber brake line(s), seals, joints and the cap breather. When contaminated with just 3% water, brake fluid boiling points can fall by as much as 100 degrees Celsius.

Should the fluid boil, when you are braking, potentially lethal vapour-lock occurs. In this scary situation, depressing the brake pedal compresses not the fluid but air bubbles that form, instead. The brakes, therefore, release and the pedal will sink to the floor.

How do I check my brake fluid?

The only reliable method is to extract a sample of fluid from your car and measure the boiling point, by heating it with a special machine. Some inexpensive DIY testers measure the fluid's electrical resistance and calculate the moisture content but they tend to give misleading and inaccurate readings.

How often should I change brake fluid?

Most car manufacturers recommend brake fluid flushes every two years. Consult your car's handbook for clarification.

What brake fluid do I use?

Two main types of brake fluid exist: glycol and mineral-based. They must not be mixed. Most cars use glycol fluids of DOT 3, 4, or 5.1 specifications, which have different boiling and cold viscosity specifications. Consult your handbook for details about the carmaker's brake fluid recommendations.

How to change brake fluid

An adept DIYer can conduct brake fluid replacement at home. The optimum method is to purchase a branded brake pressure bleeding tool from a trustworthy source. These tools use compressed air to force fresh fluid through the braking circuit, which displaces the elderly liquid via the system's bleed nipples.

Ask the vendor if such tools are suitable for your car, before committing to a purchase.

How much does a brake fluid change cost?

Brake fluid is comparatively inexpensive. Garage labour charges comprise most of a brake fluid replacement invoice.

A typical cost is around £60-£75. However, some cars, especially hybrids and electric vehicles (EV), may need more advanced diagnostic activation to open certain electrically-controlled valves within the brake system, so fluid can pass through. Therefore, expect higher charges for these vehicles.

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