Rick's Free Auto Repair Advice

Brake fluid 5.1

What is DOT 5.1 brake fluid?

It’s not DOT 5!

Many people think that DOT 5.1 brake fluid is just another version of DOT 5 silicone brake fluid. It’s NOT, and it’s not compatible with DOT 5. Do not mix DOT 5 and DOT 5.1

What is different about DOT 5.1 brake fluid?

It’s all about brake fluid boiling points. DOT 5.1 has a higher boiling point than DOT 3 or DOT 4. Brake fluid boiling points are rated on two scales; dry and wet.

Brake fluid dry boiling point

Dry boiling point is measured with the fluid containing 0% water by volume.

Brake fluid wet boiling point

Wet boiling point is measured with the fluid containing 3.7% water by volume


Brake fluid color

Fresh glycol brake fluid (DOT 3, DOT 4, DOT 5.1) is  translucent yellow color; almost clear as you pour it out of the bottle

Fresh DOT 5 brake fluid is purple color.

Over time, all glycol based brake fluids darken. But color alone is NOT an indication of brake fluid condition. What causes the discoloration? Moisture and normal rubber degradation.

The ONLY way to determine brake fluid condition is with test strips and a moisture meter or refractometer.

What is LMA brake fluid?

Low Moisture Activity brake fluid is designed to accumulate less moisture, thus resulting in a higher boiling point.

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Posted on by Rick Muscoplat


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