Brake Fluids

Brake fluid is one of the most important but least considered fluids in the car. It transfers the effort applied to the brake pedal by the drivers foot to the components that stop the vehicle. The brake fluid used in most cars is known as polyglycol fluid, a substance that looks similar to oil.

Brake fluid deteriorates over time as it absorbs moisture from the atmosphere. This reduces the fluids boiling point and causes brake system components to corrode. Heat generated from the brakes can cause water-logged fluid to boil, which causes sudden and unexpected brake failure. This is why brake fluid needs to be changed at regular intervals.

Brake fluid is very sensitive to contamination and something as simple as dipping an oily finger into a brake fluid reservoir will contaminate the system, possibly causing brake failure.

It is important to check the vehicles handbook before buying brake fluid, as manufacturers have specific requirements. Most commonly, this will be a Department of Transportation (DOT) 3 or 4 fluid.

In theory a DOT 4 fluid can be used in place of a DOT 3 fluid. However, in practice this isnt always the case, as some brake system materials are incompatible with fluids other than those specified. A DOT 3 fluid should not be used where a DOT 4 fluid is specified due to their different boiling points.

Rolls Royce is one of a few manufacturers that dont use conventional fluids, instead specifying a specific mineral oil. These mineral oils are not compatible with conventional systems and will severely damage the brake system if used.

Brake fluid is particularly damaging to paintwork so never attempt to mop up, wipe or rub spills. Spills should be immediately flushed away with plenty of water.

Due to its affinity for moisture dont use fluid that has been stored for long periods after opening.

Its normal for brake fluid reservoirs to require an occasional top up, however, any vehicle demanding frequent refilling needs professional investigation as a leak may have developed.

For further assistance RACQ Members can call RACQ Technical Advisory Service on 1800 623 456.