Brake fluid testers

Posted on January 2nd, 2019 by Rob Marshall

Brake fluid testers

Technology is a wonderful thing – in many cases, it has made tools that were once solely the preserve of the professionals more accessible to the enthusiastic car owner. A particular example of which is DIY brake fluid tools. Yet, we advise that you must buy with care.


The dangers of old brake fluid

Among the repair trade, elderly brake fluid is known as the ‘Silent Killer’. Its affinity for moisture reduces its high boiling point and this can cause contaminated fluid to boil in the braking system, creating vapour lock. This results in total failure of the hydraulic braking system, because the pedal will sink to the floor, resulting in zero retardation. Naturally, this experience for most motorists is nothing short of terrifying.


The solution is to have new fluid flushed though the braking system every two years, unless the car manufacturer (or your garage) insists on earlier intervals. Many professional workshops rely on brake fluid testers that collect a sample of your car’s fluid and heats it up to determine the temperature at which it boils. These testers cost a minimum of £300.


DIY testers (as pictured) work by assessing the electrical conductivity of the fluid and, using internal circuitry, utilising an algorithm to assess the water content. The results tend to be displayed as a traffic light system, with green for fluid in good order, through to red for brake fluid that possesses a water content of greater than 3%.


We assessed a sample of eight DIY testers on four brake fluid samples and we found that the readings varied wildly. The cheapest tester of which (that cost under £10) did not work at all and one of the other units rejected even a new sample of brake fluid as dangerous. Therefore, we do not recommend any of them but, unsurprisingly, the best of a bad bunch were also the most expensive; the Sealey VSO274 (£59.94) and the Laser 4875 (£50.35).


In short, you can use these testers as a rough guide but back-up any reading from a garage that possesses a professional test tool.