Brake Fluid Liquid Tester Pen with 5 LED Indicators, Calibrated For DOT3 DOT4 Brake Fluid

Except for the battery cover which needs some scotch tape to stay put (!!), this is indeed a very reliable and accurate brake fluid tester, and surprisingly so. Looking at the poor snap lock design of the battery cover I did not have high hopes for the rest of this device under $15. I was indeed very surprised by its accuracy to exactly measure water content in brake fluid, which is its intended purpose. I ran multiple calibrated tests with new and 3-year old brake fluid all stored in tightly sealed containers. Took exactly 5mL brake fluid samples each time being very careful in handling the sample so the sample's glass beaker was totally dry and any sample transfer syringe was also totally dry. Tested to a baseline of 0% water content. Added a drop of tap water into the brake fluid sample and thoroughly mixed it. A drop of water is generally 0.05mL, so achieves 1% water content with a drop of water added. It read exactly 1% on the tester! Then added another drop, thoroughly mixed it and tested, and it read 2% water content! Added another drop of water likewise and it read 3% water content! Added yet another drop (the 4th drop) and it read 4% water content, all as they should appear! The sensors are calibrated to be highly sensitive and accurate. Probably the only purchase I can ever recall less than $15 that is so darn accurate. Now if you all (nice manufacturer in China though they may appear German to some based on the German words on the tester) will only fix that battery cover so the AAA battery does not pop out during a test without scotch tape on it, you will really have an all-round superlative winner, and not desperately try to pass as German quality. I also looked at the brake fluid boiling point testers which are much more expensive and cover a wider range of brake fluids. Those are touted to be the most accurate. Question really is if those are even necessary for the most common every-day use with such a low cost and highly accurate electrical conductance tester available. Ultimately the boiling point of brake fluid is inversely related to its water content, and electrical conductance infers the water content based on known conductance testing references.

Works great just the color is a little different.

Perfect!!! easy to use tester

Seems to work. Indicated 3% moisture. Difficult to get the batter cover off. The on/off button is intermittent. However, once on I got an immediate reading. Of course, there is no way to verify the accuracy. I just have to trust it.

Works as it should..

I bought this back in May 2025, when I was doing one of my cars. it worked perfectly when I got it and helped me identify that I had water in my brake fluid. now in March 2026, I want to do the second car, and when I turn it on, it lights the green light with no issues, but it doesn't light anything else. I tried all possibilities, I tried cleaning the electrodes, praying them with brake cleaner, replaced battery, removed battery for few minutes and put back in. Nothing worked. So one star because it wasn't supposed to be a one time use.

Simple to use. Accurate results

El producto llego en el tiempo previsto, el contenido cumple con lo indicado en el anuncio.

Muy fácil de usar, para uso personal está excelente, para un taller usaría uno mejor. Por el precio vale la pena.

Esse produto informa, com uma certa precisão, o momento em que o fluído de freio deve ser substituído.

Quick easy way to test brake fluid.

Worked as advertised. It proved that my brake fluid was perfect, no reason to replaca all with all the work of bleeding brakes etc. I now only topped-up my brake fuid reservoir with a little fresh brake oil. So an immediate payback here.

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