Compatibility of the DOT 5 Brake Fluid

March 15, 2016 | Periodic Maintenance Info


The brake fluids are the ones which make the proper functionality of the brakes possible making them an integral part of a vehicle. Since the brakes in every vehicle are dependent on the brake fluids, it’s important to understand and comprehend their chemical nature. Understanding their chemical nature does not mean that you have to remember their chemical formulas and such stuff. You must know what sort of liquid materials are they made up of and their compatibility with other brake parts like reactions which may be harmful for the braking system.

The brake fluids are categorized with the DOT numbers like DOT 3, DOT 4, DOT 5 and DOT 5.1. The DOT is an abbreviation for “Department of Transportation”. The DOT 3 brake fluids are composed of the mixtures of glycols and glycol ethers. The DOT 4 brake fluids are also made up from mixing the glycols and glycol ethers with the addition of borate esters in them. The DOT 3 and DOT 4 brake fluids are considerably similar to the automotive anti-freeze which is made up of ethylene glycol which shows that they are cannot be counted among the petroleum fluids. The DOT 3 brake fluids are the standard brake fluids, DOT brake fluids are used for heavy duty braking systems and both the fluids are glycol based. DOT 5 on the other hand is silicone based. An easy identification of the DOT 5 brake fluids is their purple color which is due to the use of a dye.

DOT 5 Brake Fluids Compatibility

As mentioned earlier, the DOT 5 brake fluids are made of the silicone. One of up points of the silicone is that it does not absorb any moisture which means that the DOT 5 brake fluids do not get contaminated due to moisture with the passage of time unlike other conventional brake fluids like DOT 3 and DOT 4. Another advantage of the silicone is that it is chemically inert which means that no reactions between the DOT 5 brake fluids and the other parts of the braking system will take place. Its boiling point is higher than DOT 3 and DOT 4 as well and is non-toxic meaning it will not damage the paint of the vehicle like DOT 3 and DOT 4.

These features have given the DOT 5 the name of the premium lifetime brake fluid making it an ideal choice for the braking systems of the vehicles which are not used too often and to maintain the braking systems of the antique vehicles.

But all this does not make the DOT 5 a magical and perfect brake fluid since it has some limitations as well. First of all, it is very expensive and costs almost 4-5 times as that of conventional brake fluids. It will not mix with the DOT 3 and DOT 4 brake fluids as well due to formation of sludge in case of mixing. This makes the brake fluid change really difficult since all of the previous brake fluid will need to be removed before refilling the braking system with DOT 5. The physical properties and the compressibility of the silicone based DOT 5 is slightly different from the conventional brake fluids as well making it a bad choice for the ABS.

The materials used in the brake systems must have high compatibility with the brake fluids used in them. This compatibility is determined by the chemical and physical properties of the brake fluids. The DOT 5 is compatible with the most brake systems materials but there are a few exceptions where the silicone rubber external components like caliper piston boots are attacked by greases and silicone fluids.

Also Read: Burnt Automatic Transmission Fluid Symptoms

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