Antifreeze testing

Q I was interested in the mention of testing coolant with a digital multimeter in the November 2019 edition of Car Mechanics (page 10).

Could you please confirm the exact method, and also what readings would be acceptable? I have looked online but as usual the methods shown vary.

Martin Marsland

A The testing of coolant using a digital multimeter is only for an indication of its anticorrosive properties, not its ability to resist freezing. This reads the level of electrolysis in the coolant; the level needs to be kept low to ensure that the different metals within the engine are not attacked by the corrosive effect of electrolysis. This is one of the reasons that, when manufacturers specify coolant mixture, they advise using deionised or distilled water.

The acceptable level which I have always gone by is one third of a volt (0.33V), but it appears that this is an area that the manufacturers do not have a specification for. It must also be remembered that if the engine earth is poor, this can effect the test results.

The method is to place the negative terminal of the multimeter firmly on the negative terminal of the battery, with the engine switched off. Then, ensuring that the positive terminal of the meter does not make contact with any metal

within the cooling system, lower it into the coolant. You may also wish to repeat the test with the engine running; if the voltage rises, this will also be an indication of earthing problems with the engine or its ancillaries.