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Under the hood: Is cheaper brake fluid as good as the higher-priced?

Published: Friday, July 20, 2012

Updated: Friday, July 20, 2012 09:07

 

Question: I want to flush the brake system and this will take several bottles of DOT 3 fluid (DOT 3 is embossed on the reservoir top). What do you think of picking a plain DOT 3 fluid by price? Or, asked another way, the SuperTech DOT 3 is the best price and is there any point in paying more for another brand? The alternatives are house brands (O'Reilly, Auto Zone, etc.) or Wagner.

Some would reply that they pay more for peace of mind. However, is the higher-priced product really better in some way? Does the Department of Transportation require that each lot be tested against the DOT 3 standards?

Answer: It's great you're interested in renewing your brake fluid. Brake fluid attracts moisture, perhaps as much as 2 percent per year, which can lead to corrosion issues and a slight chance of degraded brake performance. The complexity and cost of your antilock brake modulator certainly makes a good case for maintaining clean fluid, and should one encounter very high brake temperature, moisture in the fluid can boil (becomes compressible) which can lead to spongy braking, or worse. It's odd that domestic vehicle manufacturers typically don't specify a service interval for brake fluid, but a majority of Asian and European makers do. Most folks familiar with brake systems would like to see fluid renewed about every two to three years, regardless of how the vehicle is driven.

Federal Motor Vehicle Safety Standard No. 116 specifies brake fluid properties, as well as how it's contained and labeled. Fluid manufacturers self-certify their fluid meets standards for dry boiling point, wet boiling point, viscosity, PH value, temperature and chemical stability, corrosion resistance, effects on rubber components, appearance _ and more ... DOT 3 and DOT 4 are the two commonly specified brake fluid types. They are compatible, but it's best to use the one the brake system was designed for. Antilock and stability-control system equipped vehicles are particularly fussy about having correct fluid viscosity (thickness) for proper operation.

Brake fluid manufacturers have plenty of wiggle room in how they engineer their fluid as long as it meets the requirements specified by Standard 116. Some may just meet a standard while others exceed them by a wide margin. Inexpensive fluid, renewed regularly is arguably equal to or better than neglected/old high-price fluid. Other standards you might look for when comparing fluid are SAE J1703, ISO 4925, and JIS K2233. My personal choice for moderately priced fluid is Castrol's GT LMA brake fluid (meets/exceeds all of the above). Brake fluid doesn't store well in plastic bottles (moisture intrusion), don't buy it by the gallon and store the leftover! Check out www.aa1car.com/library/bfluid.htm for a great article on brake fluid replacement and testing.

You didn't mention the brand/model of vehicle this is or how you plan to renew the fluid. Bleeding/flushing procedures can vary widely due to the workings of the ABS system. In many cases a simple vacuum bleeder can be used to draw new fluid throughout the system to each wheel's caliper/cylinder, but a pro-grade scan tool may be needed to command ABS solenoids to purge old fluid from the brake modulator or to enable a path for front or rear bleeding/flushing. Be sure to follow the manufacturer's recommended procedure and observe safety precautions.

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ABOUT THE WRITER
Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at under-the-hood@earthlink.net; he cannot make personal replies.

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