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I am a little puzzled about a letter I received from the Honda dealership where I purchased my CR-V last year. The vehicle is a 2019, and the letter tells me that I need to bring it back for a brake fluid change. I have owned cars from different manufacturers for close to 50 years and have never had to change brake fluid. Is this something new?
I’m betting that if you were to check the reservoirs of a random sample of 100 cars at the wrecker’s yard, you’d likely find less than 10 that didn’t still have some of their original brake fluid still in them. So why is the dealer telling you that your CR-V needs its fluid changed? The fact is that brake fluid should be replaced regularly as a part of normal maintenance.
Certain automakers make a point of encouraging this service. Take BMW, which has had this as an item in its service-reminder system since at least the mid-2000s. It is also specified in most newer Hondas. It is item No. 7 in your CR-V’s Maintenance Minder, and it’s been included on the company’s service schedule for decades.
Brake fluid is hygroscopic, which means that it absorbs moisture. It will do so through the cap in the master cylinder and through the seals and hoses in your brake system. This characteristic is why fluid should be changed periodically. Automakers that schedule a change usually advise getting one every two or three years, regardless of mileage.
There are two reasons for this. First is the reduction in the boiling point of the brake fluid as it becomes contaminated by water. The DOT 3 fluid that’s commonly used has a specified minimum “dry” boiling point of 205 C and a minimum “wet” boiling point of 140. Note the substantial difference moisture saturation makes.
Under prolonged hard braking, repetitive stop-and-go traffic, driving on hilly terrains or when towing, brake temperatures could boil the fluid in the calipers. If that happens, the result can be anything from a soft pedal to an outright lack of braking force.
The other reason — corrosion — is relevant to all vehicle owners. Most brake components are made of aluminum, steel or iron. Internal corrosion can seize pistons and parking-brake mechanisms, and it can cause leaks at seals. Metal and rubber particles also add to the contamination of the fluid. Flushing it all out is relatively inexpensive, prolongs the lifespan of the brakes and maximizes the performance of this safety system.
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