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COS Blog

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All About Brake Fluid

Jennie McRae - Tuesday, December 02, 2014

We probably all agree that "braking" is one of the most important functions of our cars, and although adding brake fluid is not a part of routine vehicle maintenance, it's important to know when, and why, a brake fluid flush is necessary.


But first: what is brake fluid, actually?--


--It's a type of hydraulic fluid used in hydraulic brake and hydraulic clutch applications in automobiles, motorcycles, light trucks, and even in some bicycles.1 It transfers force into pressure, and amplifies braking force. Most brake fluids used are either glycol-ether based, mineral oil based, or silicone based.


And have you ever wondered what the DOT numbers mean?


DOT actually stands for the U.S. Department of Transportation, and DOT 3, DOT 4, etc., are just broad classifications that reflect concerns addressed by the SAE's specs, but with local details based on temperature and humidity ranges considered when making regulations.2


Specifically, DOT 3, 4, and 5.1 are polyethylene glycol-based fluids. These fluids are hygroscopic and will absorb water from the atmosphere. DOT 5 is silicone-based and is actually hydrophobic, so DOT 5 brake fluids have a more stable viscosity index over a wide temperature range.3


Basically, it's important to know which brake fluid your system requires. And just like you wouldn't skimp out on regular oil changes for your vehicles, it's important that you don't let your brake fluid get contaminated by particles, either. It's typically a good rule of thumb to have your brakes flushed about every 30,000 miles. It is also important to note that brake flushing and brake bleeding are two different procedures. Brake flushing could be compared to an oil change--it involves removing all the brake fluid from the system, and replacing it with brand new brake fluid. Brake bleeding is when just enough brake fluid is removed to get air bubbles out of the brake lines.4


If you ever notice your that your brakes aren't performing like they should, have them inspected immediately. For more information on what brake fluid is right for your car or your fleet's engines, give us a call at 1-800-883-8081.



1. ^ "Standard No. 116; Motor Vehicle Brake Fluids". U.S. Department of Transportation. 12 Apr 2013. Retrieved 22 May 2013

2.  "MSDS for DOT 3 brake fluid". Retrieved 2012-06-04.

3. ^ Standard No. 116; Motor vehicle brake fluids Code of Federal Regulations, Title 49 - Transportation, Chapter V - Part 571 - Federal Motor Vehicle Safety Standards (49CFR571), Subpart B, Sec. 571.116 Standard No. 116; Motor vehicle brake fluids

4. http://auto.howstuffworks.com/auto-parts/brakes/brake-tests/is-brake-flushing-necessary.htm


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