Brakes and running gear
When should brake fluid be changed?
Why brake fluid deteriorates over time, how often it should be changed, the difference between DOT 3, DOT 4, DOT 5.1 and DOT 5, and what to watch when changing it.
Brake fluid absorbs moisture from the air over time. As the moisture content rises, the fluid's boiling point drops. If hot fluid boils on a long descent or after repeated hard braking, bubbles form in the system and the pedal can go to the floor.
How often?
Most car manufacturers recommend changing brake fluid every two years, regardless of mileage. The exact interval is in the service schedule. At a workshop, the moisture content can be measured in a few seconds with a brake fluid tester.
DOT types
- DOT 3, DOT 4, DOT 5.1: Glycol-based. The higher the number, the higher the boiling point in general. Use the type your car requires; most modern cars need DOT 4.
- DOT 5: Silicone-based and must not be mixed with the others. It is rarely used in ordinary passenger cars.
The type to use is usually written on the reservoir cap. You can find suitable products in the oil, antifreeze, batteries & tyres category.
FAQ
How often is brake fluid changed?
Most manufacturers recommend every two years. The exact interval is in your car's service schedule.
Can DOT 5.1 be used instead of DOT 4?
Both are glycol-based and can usually replace each other. DOT 5 (silicone) must not be mixed with them. Check your manual first.
This guide gives general information. Torque values, fluid quantities and service intervals vary by vehicle; follow your owner's manual. If you are unsure about safety-related work, ask a mechanic.
