Rick's Free Auto Repair Advice

Brake Fluid DOT4

What is Brake Fluid DOT4

Brake fluid labeled as Department of Transportation DOT 4 is made with 50 to 65% glycol ether base with 20-30 % Borate Ester to resist boiling.  The boiling point of dry DOT 4 is 450°F and 311°F when wet. Those are higher boiling points than DOT 3, but DOT 4 absorbs water about 20% faster than DOT 3 fluid.

Are brake fluids interchangeable?

DOT 4 fluid can be used in a vehicle where DOT 3 is specified, but DOT 3 should never be used on a vehicle where DOT 4 is specified because the DOT 3 boiling point will be lower than the brake system’s minimum specifications.

DOT 5 fluid can never be used in vehicles rated for either DOT 3 or DOT 4

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