Technicians urged to use brake fluid testers with caution

Careful handling and regular calibration are required if results are to be reliable, according to Apec Braking

Technicians urged to use brake fluid testers with caution
Boil brake fluid tester (left) and a conductivity brake fluid tester (right).

Some electronic brake fluid testers have been passing dangerous-to-use brake fluid while failing new fluid straight out of the bottle, Apec reports.

In one of its Tech Mate bulletins, Apec said: “You should be aware that these testers are not all of the same design and some are very much better than others.

“We are aware of many incidents where electronic brake fluid testers have incorrectly failed new product straight out of a bottle, while under different circumstances passing product as acceptable which had become dangerous for use.

“In our experience any brake fluid tester which does not actually heat the fluid is likely to give misleading or even dangerous results.”

Dangerous results

Such testers will estimate the water content electronically by measuring the conductivity or occasionally the
capacitance of the fluid, which in theory increases as water is absorbed.

The tester then converts this measurement to supposed boiling point and indicates the result commonly as a display of green, yellow or red lights, depending on the conductivity.

Apec say this measurement principle is fatally flawed as the conductivity of new brake fluids varies substantially, from not only between DOT 3, DOT 4 or DOT 5.1 types but also from formulation to formulation within a DOT grade depending on the additives used.

It means that unless a conductivity tester is calibrated on one manufacturer’s product and then used for that
product only, it is likely to give very inaccurate results.

Heating samples

Apec added: “In contrast to this type of equipment, testers are available which actually heat a sample of the fluid to establish the boiling point, thereby getting away from the problem of varying conductivity.

“In our experience these provide the best balance of performance and economy currently available.

“Electronic devices to test automotive brake fluid when in service are becoming increasingly popular.

“Correctly designed and used, they can make a real contribution to road safety, while providing profit opportunities for garages.”

For further information about Apec and for Apec’s latest bulletins, click ‘more details’ below.

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