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 but batteries die quick

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 great just the color is a little different.

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

Update June 2023: (There is an interesting video review of this tester, indicating abnormally high contamination levels in various samples of new brake fluid. The test appears to use a nearby bottle of ionized electrolyte drinking water in an effort to decontaminate the tester's probes between measurements. The ionized water could have a concentration of ions thousands of times greater than that of the contaminating water in the brake fluid. Microscopic amounts of the ionized water, shedding off the probe tips into the brake fluid samples, could be enough to alter the outcome of the conductance tests. It would be interesting to see that test rerun, with de-ionized water used to clean the probes, in lieu of the ionized water.) Original Review: While I don't have the resources to conduct an exhaustive evaluation, I was able to test the unit to my satisfaction. I started by testing the DOT 4 brake fluid in two high performance automobiles. The testing was performed by completely immersing the unit's probes into the master cylinders. Both vehicles had a brake fluid flush less than a year ago. Before immersing the tester, I switched the tester ON and verified that its green battery check light illuminated. For both vehicles, the tester showed a single yellow light, indicating water contamination of less than one percent. After bringing the tester indoors, I tried to approximate the tester's accuracy using various concentrations of tap and distilled water. When immersed in undiluted DISTILLED water, the tester illuminated only the battery check light (the expected result). When immersed in undiluted TAP water, the tester showed all of the lights, indicating water contamination greater than 4 percent (also expected). When immersed in a mixture of one part tap water and 19 parts distilled water (5 percent), the tester showed the expected result of greater than 4 percent. When immersed in a mixture of one part tap water and 39 parts distilled water (2.5 percent), the tester correctly extinguished the >4 percent LED, showing <3 percent contamination. Based on my evaluation, I have confidence in the levels reported by this tester. However, I'll add a few notes of caution: My testing showed only the contamination of fluid in the brake fluid reservoir. Unlike other automotive fluids, the brake fluid doesn't circulate, and the lack of contamination in one part of the system does not prove a lack of contamination in other parts. In my opinion, to measure the contamination with any degree of confidence, a sample of fluid from each of the brake calipers would need to be extracted and tested. Also, a part of my fairly unscientific testing was done at room temperature, and another part with only a single type of brake fluid. I've yet to determine the tester's consistency over its specified temperature range, or with other brake fluids.

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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