How often should brake fluid be changed?

I've owned cars for the past 20 years and I've always made a point of changing brake fluid every two years regardless of mileage, as per my mechanic's recommendation. I recently purchased a new vehicle and notice the service requirements make no mention of this. Have modern brake systems evolved to the point where this two-year recommendation is no longer required? – Robin, Oshawa, Ont.

Some manufacturers still recommend changing brake fluid every two years, some have moved to three- or five-year intervals, and others, as you've noticed, have removed the recommendation for periodic flushing and refilling from their maintenance schedules.

Brake fluid transfers force to the various components of the braking system when the brake pedal is depressed, so you're right to be concerned about proper maintenance.

A friend recalls his older brother, circa 1977, cursing under his breath while honing out the pitted brake cylinders of his Datsun 510. Improvements in the corrosion-inhibitors added to modern brake fluids offer increased corrosion protection, but due to the dreaded water absorption issue, flushing and replacing of fluids is still required.

Traditionally, brake fluids have been glycol-based (commonly known types are DOT 3 and DOT 4). Over time, these fluids absorb moisture from the atmosphere which reduces their boiling point and therefore effectiveness – however, a water-repelling silicone brake fluid (DOT 5) has gained popularity over the past few years.

"We now use a DOT 5 most of the time in my shop," says Mike Salkus, owner of Speedy Auto Service in Victoria, B.C. "The silicone in this brake fluid doesn't absorb moisture as fast, and that was the main reason for doing brake-fluid flushes in the past – because they would attract a lot of moisture and boil at higher temperatures on braking which would cause brake fade. With silicone it doesn't get the moisture in as fast, it doesn't boil as fast, there is less corrosion in the system, and it has a longer life."

Brake fluid types aren't easily interchangeable; you'll need to stick with your manufacturer's prescription.

"It's not like the old days where one brake fluid, or one transmission fluid, worked in all makes and models. There are so many now that you have to be aware of, and different manufacturers have different recommendations," says Salkus, who recommends a brake fluid change every six years or 80,000 kilometres. "Silicone-based brake fluid is becoming more predominant on all the newer cars, but back six or seven years ago it would only show up in the BMWs, Mercedes, Lexus and high-end cars. Now it's starting to show up in domestics, like GM and Ford. With an ABS braking system, some manufacturers use silicone brake fluid, and some don't. It really is specific to the manufacturer."

It may be that your new vehicle requires a silicone-based fluid and therefore has a reduced requirement for flushing and refilling. Some manufacturers of glycol-based fluids also claim that special additives in their products make them lifetime fluids. In addition, some auto makers say the features of their modern brake systems make them comfortable with reduced flush and refill recommendations.

First and foremost, you want to satisfy your warranty requirements, and second, if you plan to hang onto the car once it's out-of-warranty you'll to want to keep the braking components in tip-top shape.

Given the high cost of certain brake components, the peace of mind gained through this relatively inexpensive procedure makes it worthwhile. As a side note, this is not a do-it-yourself procedure. The extremely high pressures generated by modern anti- lock brake systems can put you at great risk of injury if you fail to follow the servicing procedure to the letter.

Contact your manufacturer or visit your dealer service centre for further clarification on when to change your brake fluid. If in doubt, stop at any brake or repair shop, where they can determine if the fluid requires changing with a simple litmus test.