Testing acidity in coolant, using a multimeter to measure any voltage

[daverclasper]

Hi. Has anyone done this?, and is acidity harmful anyway, in a cast iron engine (maybe attacks the head gasket)?.

lot's of stuff online, about this so was wondering?, though never come across this in old school publications etc.

Thanks Dave

 

[Josef]

If you have acidic coolant yes it will eventually corrode metal. The way to test that would be to use pH paper / litmus paper or an actual pH meter. Measuring the freezing point of the coolant would also be a good simple way to confirm it hasn’t massively degraded. It is true that pH meters work by measuring a potential difference, but this is tiny compared to what a multi meter could read, and requires special glass cells, a reference probe etc. I can’t find any source I’d consider reliable suggesting you could measure pH with a multi meter, and I didn’t come across the idea once in 12 years of chemistry education and work. If you could do basic chemistry with a cheap multi meter then it definitely would’ve showed up in undergrad labs, anything to save a bit of money! Real pH meters are expensive…

https://chemistry.stackexchange.com/questions/177901/can-a-multimeter-be-used-to-measure-ph#:~:text=It is too basic for ordinary life%2C similarly as sodium carbonate.&text=The answer to the question,way to tell the difference.

[dougbgt6]

Running the cooling system for a couple of hundred miles with washing soda and then back flushing is a great way to clean it out. However washing soda does eat aluminium so don't leave it in too long. 

Doug

[JohnD]

Dave,

Using a multimeter doesn't test the acidity or not of the coolant, it tests for a 'galvanic' voltage potential in the system.

Because of their atomic structure, two metals in the same liquid will try to exchange electrons.   This was first discovered by a Signor Volta (hence Volts!) and developed into a battery by Signor Galvani.     A flow of electrons is an electric current and the direction of flow depends on the metals.   Today they may be arranged in  a "galvanic series":

Of two such metals, the one that is higher in the table will be attacked.     This is how galvanising works - the zinc coating is dissolved, rather than the steel underneath.

When radiators were made of brass and copper, the cast iron of the engine would be attacked, but those parts are massive and such erosion wasn't significant.  But today aluminium is far more commonly used for radiators, and that metal is attacked in preference to the iron.   The result may be blockages in the rad, or leaks    This happens because there is an electric potential between them, just like Signor Galvani's original battery, and that is what your multimeter can detect.

Clip the negative lead to the negative battery terminal, and dip the positive probe in the coolant though the radiator filler.   If there is a potential of more than 0.4Volts, then  you should change the coolant, for one that contains corrosion inhibitor.

John

[daverclasper]

6 hours ago, JohnD said:

Clip the negative lead to the negative battery terminal, and dip the positive probe in the coolant though the radiator filler.   If there is a potential of more than 0.4Volts, then  you should change the coolant, for one that contains corrosion inhibitor.

Thanks folks. That's what I did John. I did the test a few times and each time the voltage started at 0.7, then dropped to 0.3 after about 6 seconds. is this ok?

[Pete Lewis]

Dave    you need to sleep easy and less worrying   Ha ! 

Pete

[JohnD]

18 hours ago, daverclasper said:

Thanks folks. That's what I did John. I did the test a few times and each time the voltage started at 0.7, then dropped to 0.3 after about 6 seconds. is this ok?

Dave that might be due to a deposit on your clean meter probe, increasing the resistance to this small potential.    Perhaps repeat, first putting a separate probe  in the coolant (mustn't touch the filler cap), then touching that with your meter probe.   But if in doubt, replace the coolant.  A good antifreeze with corrosion inhibitor isn't expensive, but the inhibitor does 'wear out' after a while.   

John

[SpitFire6]

On 23/09/2024 at 19:11, daverclasper said:

Hi. Has anyone done this?, and is acidity harmful anyway, in a cast iron engine (maybe attacks the head gasket)?.

lot's of stuff online, about this so was wondering?, though never come across this in old school publications etc.

Thanks Dave

 

Hi,
Sounds like you are testing for galvanic current.
You need to measure the voltage with the battery connected & battery disconnected. With battery connected also measure voltage with different loads on.
Cheers,
Iain.