Have you Measured Your Coolant's Voltage?
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Thread: Have you Measured Your Coolant's Voltage?

  1. #1
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    Have you Measured Your Coolant's Voltage?

    With engine cool and a voltmeter set to 1V D.C. resolution, stick the positive probe into the coolant neck and immersed a good portion of the probe into the coolant. With the negative probe, touch the battery ground or a good ground on the engine, read your voltage.

    With 30K miles on the Honda blue coolant, I got 0.269 volt.

    With 7 qts. new Honda blue coolant, I got 0.230 volt.

    This surprised the hell out of me because on my 4 cylinder Toyota, it was initially 0.28 volt then after coolant replacement, I got 0.169 volt.

    On my RX7 in which I run a coolant that does not have any water at all (Evans NPG+) I got 0.069 volt after 5 years and 30K miles.

    The lower the voltage the better because there is no cathodic reaction between dissimilar metals with the coolant acting as the electrolyte.

    What are yours with miles on the coolant etc..?

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  3. #2
    Registered User 0dyfamily's Avatar
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    269mV? Do you have any voltage leaks or bad ground straps? That seems pretty high. 230mV seems high, too.

    169mV on your Toyota seems high, as well.

    69mV with a propylene glycol coolant like Evans NPG+ seems high, too. Did you get all the water out before adding that new coolant? Still, a glycol is an alcohol, it will hydrogen bond and have some ionic potential....so I guess this is to be expected.

    It's been years since I studied this stuff (solutions chemistry and redox potential), but IIRC your potential for aluminum in conventional 50/50 coolant should only yield a number in the teens (15mV to 19mV).

    I'm wondering if today's engines have so many dissimilar metals wetted by the coolant that they simply give high readings like that.

    EDIT: Well, I did a little google searching... I found that Volvo recommends a coolant change at 0.9V (900mV!!!!) I don't think I could wait that long for that to happen. To me, it seems that high of a difference in potential in a fluid without additives would cause your radiator to destroy itself from the inside-out within a month. As well, I found that some Ford mechanics say that anything below 300mV is acceptable. I guess those coolant additives (like weak organic acids) do really work.

    I dunno. If I ever saw anything close to 1V (1000mV), I'd be pulling fuses (one-at-a-time) to see if the voltage reading on my VOM changed to confirm a current leak from a circuit, then get it fixed.

    When I change the coolant at the recommended interval, I may go with a propylene glycol type. I've known people who've used these for years with zero problems. Pricey? Yes. Reliable? So far.

    OF
    Last edited by 0dyfamily; 07-30-2009 at 08:08 AM.
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    Registered User coppertop808's Avatar
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    Thats pretty wild. I understand the concept but had never heard of doing this. Will have to give it a try....
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    When I change the coolant at the recommended interval, I may go with a propylene glycol type. I've known people who've used these for years with zero problems. Pricey? Yes. Reliable? So far.

    OF [/B]
    The PPG type coolant has only 2/3 heat transfer property of the normal EG coolant. Hence, if you run with the PPG type, you must have larger radiator and higher volume pump to get the same heat rejection.

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    won't it depend upon the metal used in the probe?
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  7. #6
    Registered User 0dyfamily's Avatar
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    Originally posted by pomanferrari
    The PPG type coolant has only 2/3 heat transfer property of the normal EG coolant. Hence, if you run with the PPG type, you must have larger radiator and higher volume pump to get the same heat rejection.
    Are you sure about this? I'm fairly positive that mass for mass, propylene glycol, whether it be a vicinal diol (this is the prevaling isomer you'll find in that gallon jug) or geminal diol, has a higher heat capacity than ethylene glycol. The longer hydrocarbon backbone (i.e., more covalent bonds) is the key. I'll bet the propylene glycol is more viscous than its ethylene glycol cousin, though.

    Originally posted by brians
    won't it depend upon the metal used in the probe?
    Yes. I guess you'd want a probe setup that uses aluminum at both ends (the one in the coolant, and the one pressed against the negative battery post).

    OF
    Last edited by 0dyfamily; 07-30-2009 at 01:49 PM.
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  8. #7
    Super Moderator dvpatel's Avatar
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    I am still scratching my head as to why some one would measure the voltage of the coolant and dump 120K mile coolant at 30K.

    When I use this smilie ===> I am NOT calling you stupid.

    The value of a forum such as this one is not in that one can post a question and receive an answer, but in that the question has most likely been asked before, and the answer is available to him that will but only use the search function.

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    I lost an engine using the long-life Dexcool orange coolant in the early 90s due to cathodic corrosion. From then on I have never trusted the so-called "long life" coolant. Hence, coolant change whenever the voltage rises to higher than 0.25 volt. It just happens that this is usually at 30K.

    The Honda Blue Coolant is supposedly 5 years 60K coolant, not 120K service life coolant.

  10. #9
    Super Moderator dvpatel's Avatar
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    Originally posted by pomanferrari

    The Honda Blue Coolant is supposedly 5 years 60K coolant, not 120K service life coolant.
    The original factory fill is the 120K coolant. The replacement blue is 60K coolant so I hear and read on here.
    When I use this smilie ===> I am NOT calling you stupid.

    The value of a forum such as this one is not in that one can post a question and receive an answer, but in that the question has most likely been asked before, and the answer is available to him that will but only use the search function.

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    ..... Tranny strarted slipping only 8,414 miles after the replacemnt.
    ..... 2nd tranny replacement 9/21/2009 @ 76,659 miles.
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  11. #10
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    Hello Pomanferrari,

    This is very interesting...

    When I put the negative probe on the battery negative post and dip the positive probe into the coolant, I end up with negative 0.230 volts.

    I also noted that when I moved the probe from the negative post of the battery to the positive post of the battery I got full battery voltage.

    In doing a little research on this, I noticed that there were several comments about checking older hot rods that had been modified with aluminum heads. I believe they use the older universal green coolant. I ran a check on 50/50 green and came up with about 0.180 volts, but this was not done inside a coolant system but in jars on the bench. I got 0.250 volts from tap water.

    At any rate, the hot rod recommendation is to be concerned when you read 0.500 volts, and be sure to change the coolant before it reaches 0.700 volts.

    I also checked some orange coolant in a diesel truck that was close to being due for a coolant change, and it came in at 0.360 volts. Recently changed orange coolant checked out at 0.240 volts.

    I am not convinced that this is a valid way to determine when to change coolant. Most people are more interested in PH and monitoring the concentrations of other chemicals in the coolant.

    Another thought is that the ORP (Oxygen Reduction Potential) of the coolant may give a better clue as to what is going on. ORP can be related to PH in most cases, but there are times when it does not correlate. This deviation may be a clue, but without extensive testing it is very difficult to know.

    ORP is measured in millivolts. Green 50/50 comes in at -25 mV, the Honda coolant comes in at +40 mV, and the orange coolant comes in at +70 mV.

    I really don't know what all of this means, but it is interesting. I will have to track my coolant over time and see what happens.

    Tom

  12. #11
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    SilverFox - thanks for your input. I agree that it isn't the end all and be all factor for replacing coolant. It is almost like the TDS meter, the TDS meter will tell you the ppm of total dissolved solids but not what those solids are.

    What got me concerned was that the drop off was not significant (from 0.269 to 0.23 volts) with 80% coolant change. But since your number is similar to mine, I'll sleep better at night.

    Question for you: how do you measure ORP?


    Originally posted by SilverFoxCPF
    Hello Pomanferrari,

    This is very interesting...

    When I put the negative probe on the battery negative post and dip the positive probe into the coolant, I end up with negative 0.230 volts.

    I also noted that when I moved the probe from the negative post of the battery to the positive post of the battery I got full battery voltage.

    In doing a little research on this, I noticed that there were several comments about checking older hot rods that had been modified with aluminum heads. I believe they use the older universal green coolant. I ran a check on 50/50 green and came up with about 0.180 volts, but this was not done inside a coolant system but in jars on the bench. I got 0.250 volts from tap water.

    At any rate, the hot rod recommendation is to be concerned when you read 0.500 volts, and be sure to change the coolant before it reaches 0.700 volts.

    I also checked some orange coolant in a diesel truck that was close to being due for a coolant change, and it came in at 0.360 volts. Recently changed orange coolant checked out at 0.240 volts.

    I am not convinced that this is a valid way to determine when to change coolant. Most people are more interested in PH and monitoring the concentrations of other chemicals in the coolant.

    Another thought is that the ORP (Oxygen Reduction Potential) of the coolant may give a better clue as to what is going on. ORP can be related to PH in most cases, but there are times when it does not correlate. This deviation may be a clue, but without extensive testing it is very difficult to know.

    ORP is measured in millivolts. Green 50/50 comes in at -25 mV, the Honda coolant comes in at +40 mV, and the orange coolant comes in at +70 mV.

    I really don't know what all of this means, but it is interesting. I will have to track my coolant over time and see what happens.

    Tom

  13. #12
    Registered User 0dyfamily's Avatar
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    TDS meters are conductivity meters. That's it. They may be some solids that contribute so poorly to solution conductivity that you end up with unrealistically low "TDS measurements." I don't think they use a reference electrode.

    These days you measure ORP with an ORP "probe" (it's really two electrodes, but since they're in the same casing, it looks like a single probe). If I'm right, one of the electrodes is a reference electrode made up of a particular metal.

    It measures the voltage across a circuit, the circuit being those two electrodes and the fluid in between the electrodes.

    Just to go back to basic solutions chemistry, good oxidizers are those chemical species that are good at taking electrons from other species (which are then "oxidized"). The oxidizer that gains an electron is "reduced"...I remember this by thinking of it this way: By picking up that extra electron, the oxidizer endures a reduction in the electrical energy that makes it able to get more electrons. This is the gist of redox (reduction-oxidation) in chemistry.

    Depending on the reference electrode (I am on shaky ground...do ORP probes manufactured today use a standardized reference?), in general, the more negative the number is (in millivolts), the greater the oxidation potential of the fluid. That's not good for our engine coolant systems. Positive numbers are on the side of having more reductive potential.

    I'm at the limits of my knowledge. It's been years since I used this stuff.

    OF
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  14. #13
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    Hello Pomanferrari,

    As Odyfamily indicated, you measure ORP with a PH meter that is able to display millivolts and an ORP probe. While it is possible to use a PH probe and just read millivolts, you get better results with the ORP probe because it has a reference junction inside it.

    Usually, ORP directly correlates to PH, but not always. Thus the need for the ORP probe. If you pick one up, be sure to also pick up some calibration fluid. The ORP probe has a limited life time, so it is necessary to check its calibration frequently.

    Be advised that ORP measurements can be difficult to interpret due to a lack of standards to compare the readings to. However, we may be able to break new ground by simply tracking the ORP of the coolant over time. If we can get several people to do this, we will end up with something close to a study.

    Tom

  15. #14
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    Hello Odyfamily,

    You are close, but you have it backward.

    Positive numbers indicate oxidation potential. Negative numbers indicate reduction potential.

    At least that is the way it is with the probe I am currently using.

    I picked up my meter and probe from Cole Parmer.

    Tom

  16. #15
    Registered User 0dyfamily's Avatar
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    Got it. It's been decades since I worked with this stuff. I can do the equations, but just can't use this newer gear (well, it looks newer, but it all works the same as it used to.)

    Cole Parmer is a great place to get test gear, or stuff for test gear (in my case, thermocouple jacks).

    OF
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