Breaking Down the DOT Ratings for Brake Fluid

Mar. 1, 2022

This video is sponsored by ADVICS. With over 30 years of OE expertise, ADVICS engineers and manufactures the aftermarket most advanced ultra-premium brake products.

Brake fluid is so important to the safe operation of vehicles that are regulated by the US Department of Transportation or DOT. Before it hits the shelf, the brake fluid must pass DOT testing for its ability to stay fluid at low temperatures, resistant boiling and high temperatures and other specifications. When you’re selecting brake fluid for a customer, you’ll see different options based on the product’s DOT number with each number indicating a higher brake fluid boiling point. For example, DOT 4 brake fluid will have a higher boiling point than DOT 3 brake fluid.

We can group brake fluids into one of two categories, glycol based, or silicone based. DOT 3, DOT 4 and DOT 5.1 are glycol-based brake fluids comprised of mineral oils, esters, glycol esters and synthetic oils. While DOT 3 brake fluid, DOT 4 brake fluid, and 5.1 brake fluid technically are compatible, it’s generally not recommended that you mix different fluid types, and your customers should never mix silicone and glycol-based fluids. Most vehicles use DOT 3 brake fluid. It’s been around since the 1980s and it’s designed for what you might call normal driving conditions. DOT 3 brake fluid absorbs less water from the air over time than DOT 4, which means it has to be changed less frequently. Certain types of driving conditions will accelerate the breakdown of DOT 3 brake fluid such as hard braking, towing, racing, or going downhill for extended periods. Compared to DOT 3, DOT 4 brake fluid has higher wet and dry boiling points, which yields better performance and higher braking temperatures and in high performance applications. Although DOT four is becoming more popular, you’re mainly going to see it in European nameplates. There are several different variations of DOT four brake fluid, so be sure that you’re selecting the correct type for your customer.

When you’re recommending a DOT 3 or DOT 4 brake fluid, keep in mind that quality does matter. In the previous video, we talked about the critical role that brake fluid plays in transferring hydraulic pressure from the brake pedal to the caliper or cylinder at wheel. New to the automotive aftermarket, DOT 3 and DOT 4 LV brake fluids from ADVICS are ultra-premium synthetic formulations that are designed for and tested by the OEMs. Distributed through Aisin, these American-made brake fluids offer industry-leading wet and dry boiling points, which we’re going to talk about in the next video.

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