Common misconception
Many people find brake fluids to be a difficults problem to tackle in order to properly care for your vehicle. However, by using the Deparptment of Transportation's (DOT) safety rating, you can easily understand the differences betweeen brake fluids in a matter of minutes. The brake fluid that you use should be rated either DOT3, DOT4, or DOT5, or even higher. Look for information directly on your brake fluid product. These levels are based on the boiling point of the fluid, due to the excruciatingly hot environment that brake fluids are forced to perform well in. For example, a DOT3 product has the minimum boiling point requirement considered sufficient by the Department of transportation, while a DOT5 product will perform well in conditions of a more extreme nature. While a DOT5 product is considered the highest rated, this may not mean that these are the best fluids for your car. There are various advantages and disadvantages to all fluids. Below is a information on the pros and cons of DOT3-5 and DOT5.1 brake fluid ratings.
DOT 3pros: Cheap and available almost anywhere.
cons: This fluid is very hygroscopic, meaning its easily absorbs water vapor from the air. This is problematc due to the corrosion that water causes once it enters the braking system. You should not put DOT3 brake fluid into your car after it has been open for several weeks. DOT3 brake fluid also wears away paint. -boiling points are 401 F DRY and 284 F WET -polyglycol ether based |
DOT 4pros: Widely available.
DOT 4 fluid has a higher boiling point than DOT 3 gradients, making it perform better in hotter brake systems. Also, DOT 4 fluid is not nearly as hygroscopic as DOT 3 fluid. cons: DOT 4 fluid will still wear off paint and allow for oxygen exposure. DOT 4 fluid is still slightly hygroscopic, and more expensive than DOT 3. -boiling points are 446 F DRY and 311 F WET -polyglycol ether based |
DOT 5pros: DOT 5 fluid does not corrode paint, and is not hygroscopic at all. It also has a boiling point higher than DOT 4.
cons: DOT 5 fluid is very expensive. It also is the only silicone based fluid, rendering it incompatable with all other fluids. Therefore, if you wanted to convert your car to a DOT 5 product, you would essentially need to disassemble and reassemble your entire brake system.If moisture does get into a silicone based fluid system, it will cause deterioration of the mechanisms because the vapor is trapped and cannot get out. -boiling points are 500 F DRY and 356 F WET -silicone based |
DOT 5.1pros: DOT 5.1 fluid is a polyglycol ether based fluid, relating it back to, and making it compatable with, DOT 3 and DOT 4 compounds. It also prevails over the other three types mentioned here regarding performance and boiling points.
cons: Like the other two polyglycol based fluids, DOT 5.1 will deteriorate paint and absorb moisture. DOT 5.1 is also very expensive and difficult to find. -boiling points are 518 F DRY and 375 F WET -polyglycol ether based |