Brake fluid

Grades, and the number on the label

Updated October 2026

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What the manufacturer has to give the packager So the information flows down the chain The grades Why wet, not dry Which makes the seal a performance matter Mineral oil is a different product Lot traceability is part of the package References

The grade and the wet boiling point are label content, and the inner seal is what keeps the second one true.

What the manufacturer has to give the packager

S5.2.2.1 requires the fluid manufacturer to furnish each packager, distributor or dealer with a serial number identifying the production lot and date of manufacture, the grade, the minimum wet boiling point in Fahrenheit, and certification that the fluid conforms to 571.116.

So the information flows down the chain

A packager cannot invent any of those four. If you are filling someone else’s fluid, that paperwork is the input to your label, and a missing certificate is a reason not to fill rather than a detail to chase later.

The grades

DOT 3, DOT 4 and DOT 5, with DOT 5 further distinguished as DOT 5 SILICONE BASE or DOT 5.1 NON-SILICONE BASE. The standard defines a silicone base fluid as one containing not less than 70 percent by weight of a diorgano polysiloxane.

Why wet, not dry

The wet boiling point is measured on fluid that has taken up water, which is the condition brake fluid reaches in service. It is the conservative number and it is the one the label carries.

Which makes the seal a performance matter

Absorbed moisture lowers the boiling point, so a container that breathes is quietly falsifying the figure printed on it. That is the clearest link in this library between a closure component and a published claim.

Mineral oil is a different product

Hydraulic system mineral oil has its own paragraph, its own designation in capitals at least 3 mm high, and a warning that it is NOT COMPATIBLE with the rubber components of systems designed for DOT fluids. Do not reuse brake fluid artwork for it.

Lot traceability is part of the package

A serial number identifying the packaged lot and the date of packaging has to be on the container. That is a filling-line discipline rather than a design one, and it is the item most often left as a placeholder.

References

49 CFR 571.116 S5.2.2, on certification, marking and labeling: seven required items on the container or a permanently affixed label, never on a removable part such as a lid, including the DOT grade, the minimum wet boiling point in Fahrenheit, a packaged-lot serial number and four verbatim safety warnings. S5.2.2.4 moves the labeling to an outer carton where the container is not normally visible. law.cornell.edu

49 CFR 571.116, Federal Motor Vehicle Safety Standard No. 116, Motor vehicle brake fluids. S5.2.1 requires every container of 177 mL or more to have a resealable closure with an inner seal impervious to the fluid and a tamper-proof feature destroyed or substantially altered on first opening. law.cornell.edu

Written from federal regulation and from measured catalog data, not from a blending bench. We sell containers and closures; whether a particular closure satisfies a particular clause is a question about that closure and its supplier’s testing, and nothing here certifies a package as compliant. Anything on these pages is a starting point.