voltage test for coolant condition

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Oct 21, 2015
Hello folks. Has anyone done a voltage test on their coolant to test for additive depletion/electrolysis? I ran across this test on a few YouTube videos and internet sites. Basically, you measure the voltage between the coolant and the negative lead of the battery. Some sites say 0.3V or less is good and other say it should be much lower. https://www.youtube.com/watch?v=mBXZtfzHhig (change above 0.07V) https://www.youtube.com/watch?v=x-gceYx_3RE (change above 0.33V) http://www.ve-labs.net/electrolysis-101/how-to-test (change above 0.3V) So I was planning on doing a coolant change and when I ran across this test I tested the old coolant. I only got 0.005V (and noted the voltage dropped to zero within seconds unless I "stirred" up the fluid a bit again) . I also looked up the change interval in my factory service manual, I noted it says to change the green coolant every 30k or 24mo and it has been way over 24months, but also way less than 30K (probably 15-20k). So, I'm wondering: 1. why the discrepancy between these threshold values for good and bad coolant? 2. have I done something wrong in the test that I only got 0.005 volts (note I did it with engine cold and not running and ignition completely off - some sites say you should conduct the test with engine warm and running). Also I have a very inexpensive DVM from Home Depot but it works fine for checking my hobby LiPo batteries and the like. 3. is it possible the coolant formulation has changed since 1995 such that these coolants last much longer than 30k/24mo and the reading is truly accurate? I know this is true for engine oil quality which has certainly changed in 23 years! Very curious what values other folks have measured (if in fact anyone has!). Thanks!
Meter error. Measure 5-300mV with a cheap meter doesn't work. The tolerances are way too high. A calibrated Fluke meter or the like is required. Properly zeroing internal resistance of the leads should also be done before testing.
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Actually voltage numbers down to .005 require a laboratory with specially calibrated instruments. Buy a regular ball tester to test freeze/boil protection and change out at manufacturers stated intervals for additive protections.
I have a high accuracy FLUKE brand meter and I have gotten some screwy numbers at times doing this test. And it can vary with the point you use for the ground. Ideally it should work just as well with any solid ground point of the car in the engine bay area near the battery . It's helpful if you can get consistent readings on several successive tests. And for me, the longer I left the probe in the water....the more the number changes. When I tested some very old coolant it did give me in the 0.5 to 0.7 V range. So the test does have some value.
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Thanks all. My meter was definitely inexpensive but on the other hand, electronics are made more economically and affordable all the time. Also, I checked my owner's manual for the DVM and for the 0-200 mV range I used, it has a specified accuracy of +/- 0.5% of reading +/- 3 digits. So even at 10 mV for example, that would put the accuracy at 10.0 +/- 0.4 mV since the meter reads to the tenth of a mV on that range. I agree with 69GTX that a stable reading is not trivial to obtain probably because it is a solution measurement.
Obviosly we are measuring voltage created by acid reacting to certain metals in the cooling system so I measure from the center of the fill acess to the closest piece of metal. It would seem that a copper/brass radiator would give a higher reading than an aluminum radiator with plastic tanks. I use an inexpensive digital and a decent analog meter and if they don`t agree I trust the analog thats been compared to a friends Fluke. Digitals tend to hunt, the analog is damped.
Originally Posted by Dinoburner
... Digitals tend to hunt, the analog is damped.
But the analog probably requires more current, partially shorting the voltage you're trying to measure.
Originally Posted by Snagglefoot
Most coolants are good for 5 years and you can do a Bitogger strategy and lower that to what you want.
^This No harm in changing it early. It is a good way to get out of the house when one needs a break from the honey do list. And it helps to keep the car on the road. And the little syringe style coolant testers can be used as further evidence for the coolant condition. Personally I have more faith in them, vs a multimeter, for coolant condition. However I usually change mine at the recommended interval or less, so it is really a moot point for me.
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Don't forget that the meter leads and tips themselves have a small amount of resistance. When the voltage dropped over the circuit in the millivolt range is used there is already inaccuracy down to the second decimal place. When reading resistances this small, a device such as a wheatstone bridges is typically used. It seems maybe an instrument that reads conductivity should actually be used reading Siemens/Meter for accurate diagnosis.
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I don't subscribe to the .3v thing. My own rule is .2v or less. Well.. Actually .22v but most meters won't read that accurately. Check the electrode potential difference between Aluminum and Iron for why I say this wink
The analog meter we us is self powered with a 1 1/2 and a 9v battery but the meter test isn`t the be all end all in determining when to change antifreeze. My 1949 Farmall goes about 10 years without changing. It has no water pump using instead the thermosiphone principal. The Equinox will will not be changed until 100,000 passes, the 95 GMC was done at 95,000 when the water pump gave up.
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