Brake fluid

The immersion test

Updated October 2026

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The procedure The pass condition Why the cut is there What usually fails Run it before you buy the labels Direct marking avoids the adhesive question Keep the tested sample References

A packaging test you can run on a bench this afternoon, written into a federal safety standard.

The procedure

If the container has a label affixed to it, make a single vertical cut all the way through the label with the container upright. Immerse the container in the same fluid it holds for 15 minutes at 23 plus or minus 5 C. Within 5 minutes of removal, wipe the excess off with a clean dry cloth.

The pass condition

The required information must be legible to an observer with corrected visual acuity of 20/40 at a distance of 305 mm, and the label must not be removable without being destroyed or defaced. Both halves have to hold after the immersion.

Why the cut is there

It gives the fluid a path under the facestock, which is exactly how a label fails in a vehicle bay: a scuff or a nick, then fluid wicking behind the adhesive. Testing an intact label would not find it.

What usually fails

Ink that smears or lifts, a facestock that swells or goes translucent, and an adhesive that releases at the cut and lets a corner curl. Those are three different suppliers’ problems and the test does not care which one you have.

Run it before you buy the labels

A few blank or proof labels on a filled bottle, fifteen minutes, and a tape measure at 305 mm. It is the cheapest test in this property and it is the one that decides whether your print order is usable.

Direct marking avoids the adhesive question

Information marked directly on the container surface has no facestock to lift and no adhesive to release, which is why the rule allows it explicitly. It is a tooling and process decision rather than a print one.

Keep the tested sample

Immersed, wiped, dated and filed with the label specification. It is the evidence that the combination you bought was the combination you tested, and it costs one bottle.

References

49 CFR 571.116 S6.14, Container information: cut the label vertically all the way through, immerse the container in the fluid it holds for 15 minutes at 23 plus or minus 5 C, wipe it dry, and the required information must remain legible to an observer with 20/40 vision at 305 mm. law.cornell.edu

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

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.