Know the Difference Between DOT3, DOT4 and DOT5 Brake Fluid

You rely on a good braking system to safely operate almost any powersports vehicle, and for that braking system to function properly it needs to be maintained with the correct type of brake fluid. Failure to maintain the braking system or using the wrong type of brake fluid could cause the brake system to deteriorate or even fail unexpectedly.

To understand brake fluid ratings we have to touch on what brake fluid does. Vehicles with hydraulic brakes (as opposed to brakes actuated by a cable) use brake fluid to transfer force from a brake pedal or brake lever to the brake caliper or wheel cylinder, which converts the force to pressure. When the caliper or wheel cylinder exerts pressure on the brake pad and rotor combination, or the brake shoe and drum combination, the friction slows the vehicle down.

That friction creates heat, and that’s where brake fluid ratings come in. The DOT (Department of Transportation) rating for a particular brake fluid represents its boiling point temperature in degrees Fahrenheit when dry or wet. Brake fluid with a DOT3 and DOT4 label contain glycol, which attracts water. Over time it is normal for brake fluid to absorb a small amount of moisture from the atmosphere. The “wet" boiling point rating is the temperature at which the brake fluid will boil with a moisture level of about 4 percent. Because it’s a liquid, brake fluid is not compressible; when you push the pedal or squeeze the lever, almost all of that force is turned into braking power. However, if there is water in the brake fluid and the brakes get hot enough to cause that moisture to boil the moisture becomes a gas (steam), which can be compressed. This can cause the brake control to feel “mushy" and reduce braking performance. In an extreme case your brake lever might go right to the handlebar. Moisture in the braking system can also cause corrosion in the brake calipers or cylinders, which can lead to brake fluid leaks and other inconvenient problems.

Keeping brake fluid as “dry" as possible is why most vehicle manufacturers recommend changing the brake fluid on a regular schedule. Check your owner’s manual or consult a service professional for brake system service intervals for your vehicle. The owner’s manual will also show you how and when to add brake fluid to a master cylinder reservoir. That level can go down as new brake pads wear. Finally, the owner’s manual will tell you which type of brake fluid is compatible with the brake system in your vehicle. It’s very important to only use that type of fluid when servicing the system or topping off the reservoir. The specified type of fluid is also almost always printed on the cap of the reservoir.

Most applications call for a DOT3 (401 F dry/284 F wet) or DOT4 (446 F dry/311 F wet) fluid. DOT4 brake fluid, such as Quicksilver DOT4 Brake Fluid, is considered a higher-performance fluid since it can handle more heat. While both fluids are glycol ether based, DOT4 contains a certain amount of borate ester, which allows it to handle more heat.

DOT5 is a silicone-based fluid that was developed for use where moisture or water is almost certain to be a factor in the braking system, such as motorcycle applications. While DOT5 fluid, such as Quicksilver DOT5 Brake Fluid, has a higher boiling point (500 F dry/356 F wet) than DOT3 or DOT4, it exhibits more compressibility than glycol ether brake fluid.

DOT3 and DOT4 should never be mixed with DOT5 fluid. They're incompatible, and brake failure may occur if mixed. Moreover, there are serious compatibility issues when using DOT5 in a system that was engineered to use DOT3 or DOT4. Also, users should take care not to mix DOT3 and DOT4 fluids as there could be brake system compatibility issues. Always consult your owner’s manual and use the type of fluid specified for your vehicle.

Premium Quicksilver Brake Fluid products meet applicable Federal Motor Vehicle Safety Standards and manufacturer specifications. Each is packaged in a convenient 12-ounce, pour-top bottle. You can shop Quicksilver Brake Fluid products online. 

Once the container is opened, brake fluid has a very short shelf life. If you need to add some fluid or are servicing your own brake system, always use brake fluid from a fresh, previously unopened container.