Testing coolant with multimeter
 

It's been three years since I last did the coolant service, so according to the Mercedes service recommendations, it's time to do it again. I have typically always done it every three years. However there are only about 5500 miles on it in the last three years. The coolant is nice and clear and good to -40. I want to check it with a multimeter, but need to know the numbers, i.e. what setting on the multimeter do I use and what results tell me to let it go for another year or two?

Thanks.

I don’t think you should see any stray potential.

What coolant did you use? Those with silicates will have some drop out over time.

Above .4v with engine running and warmed up above .44 and the coolant has picked up enough metal particles to be of concern.

What’s your basis and do you know the rationale?

If the engine (alternator) operating induces stray currents, that’s a different problem. I’d think of you saw that we would want to ensure that the radiator, heater core, etc are the same potential. Maybe that’s not 100% possible?

Using the multimeter to look for galvanic potential between dissimilar metals and components, where the antifreeze may be a conductive medium. Different phenomena. I thought the potential for that was much lower????

Here are my notes from 2020:

Coolant service done. Drained out almost 10 quarts. Replaced with 50-50 mix of Zerex GO5, distilled water and added a bottle of Water Wetter. Coolant was very clean.
Suggest maybe going four or five years for the next change. 220,873 miles

I'll try to take a multimeter reading tomorrow.

I was taught that in the 60's with large diesel equipment which needed to run continously for 9 or 10 months of the year. I was always under the impression the coolant became more conductive as metal particles became suspended in the coolant. As far as I know it's just a simple chemical reaction in a moving liquid so electro potential will result..

Thanks. The odd thing is that metal particles don’t affect conductivity for the electrochemical reaction; it’s the ions. So metal and the ionic components allow the transfer of current is what is dissolved in the water.

Decades ago when I was taught this the standard was .1 VDC .

I'm curious to see what is found in your testing .

I was curious to see what a "cold" not running test would yield. So this morning I just did a quick test of the coolant overflow tank and it read 0.0v. Is that useful at all?

Test Results
 

Maybe .

Detail where and how to placed the voltmeter's test leads .

Positive lead in coolant reservoir - negative lead to ground.

Yes but where did you attach the ground lead ? .

Be specific .

Nate - tell me more please. What do you mean by "attach the ground lead?" Do I not just stick the positive in the coolant and put the negative on a random ground spot?

I’d suspect that’s exactly the reason why it was asked. Consistency is key. And I suspect that the potential between certain spots and circulating currents locally to specific items could be the case.

I think the starting point would be the battery negative. But a bad connection to there may result in a different potential than say an aluminum head, iron block, etc.

That's My Question ~
 

Why I asked : where and how did you connect the negative lead ? .