>Newsgroups: rec.autos.tech
>From: bohdan@cbnewsd.cb.att.com (bohdan.l.bodnar)
>Subject: Re: TESTING of antifreeze chemical balances?
>Date: Tue, 10 Nov 1992 14:51:22 GMT
>
>In article <1992Nov7.191310.1@sscvx1.ssc.gov> schludermann@sscvx1.ssc.gov
>writes:
>> What are the paramters to test in ethylene gycol antifreeze?
>
>These are the tests I use: 1). specific gravity 2). EMF generation.
>
>The specific gravity can be tested with a hydrometer (I use a REALLY cheap
>one); I set my mixture so that the freezing protection is roughly -25F.
>If you really want to be exotic, use a refractometer to check the specific
>gravity (you'll get the same results as with a good hydrometer). The
>second test is based on a SAE publication from 1980 (it's in a book whose
>title is something like COOLANT TESTING: STATE OF THE ART). You'll need a
>digital voltmeter (or a high impedance analog meter accurate around the 500
>mV range). One probe is grounded and the other one is inserted into the
>radiator's filler cap. If the read voltage (ignore polarity) is less than
>300 mV, the corrosion protection is good (on my cars, I read 100 mV). 300
>mV to 500 mV is marginal, and above 500 mV the coolant should be replaced
>immediately. The book also covers corrosion electrochemistry, corrosion
>protections, and a prototype corrosion sensor which, for some reason, never
>made it into the market. My recollection is that scientists at GM
>developed this test and this sensor.
>
>Hope this helps.
Lawrence Buja so eloquently asks:
"So do think that the voltage corrosion test is BS or not?"
Hmmm, ... don't know. My first thought is that, yes, it is BS. It would
seem that the metallurgy of the engine and its components would have more
to do with any voltage you would measure in this manner, not to mention the
composition of the probe tip you dipped into the anti-freeze. But, then
again, cathodic "corrosion" of dissimilar metals in an electrolyte is
really a battery, so if the antifreeze were not pH neutral, you could see a
potential, though I'm not sure if the probe tip would be the anode or
cathode, and what would make up the other side of the "battery": the
radiator; block; head; steel cylinder sleeves; etc.
So I decided to check out a few examples. First the family mini-van: This
has a 50%-50% mix of Prestone that I put in about 2 years ago after I
replaced the blown head gasket. (It also has an iron block, alloy head,
and a brass radiator with plastic end caps.) Putting a DMM probe tip into
the antifreeze in the top of the radiator gives a very low reading: +20 to
+30 mV. This seems reasonable, since the antifreeze looks clear and the
radiator clean. So I next tried the antifreeze in my truck, which is Real
Old. (I don't remember when it was when I flushed & replaced it - the
truck is 8 years old, so the Prestone in it could be as much as 5 years
old.) (The truck also has an iron block, alloy head, and a brass
radiator.) Sure enough, the radiator looks a bit scummy, like it could use
a good boiling out and a flush. And the DMM reads: +70 mV. Hmmm, I would
have expected more. Okay, last test: The TR4. I just flushed the cooling
system in it 2 months ago and put in a 50%-50% mix of Zerex. And it reads:
-250 mV! Wait a minute - why so high?? Could it be because the TR is
negative earth and I'm seeing some electrical leakage? I disconnected the
battery - no change. It's either because of the all iron construction of
the engine, or the chemistry of the Zerex versus Prestone in the other
cars. (Makes me want to pick up a gallon of Prestone, flush out all the
Zerex and test it again.)
So, my conclusion from this terribly non-scientific investigation is that
there are probably too many variables to use the "DMM test" to check for
the amount of corrosion protection in your anti-freeze.
I suppose there still could be something to the test, but I wouldn't expect
the newest anti-freeze to give me the highest reading, even though the
reading was still within the "Ok" range given above. I suppose I could
drain the cooling system in the TR and re-fill it first with vinegar, then
muratic acid, then sea water, and test each one of these solutions, but I'm
too lazy for that! (Thank goodness!)
If I do replace the anti-freeze in the TR4 with Prestone and re-test, I'll
let you know what I find out.
Pat Vilbrandt John Fluke Mfg. Co., Inc. Everett, Washington USA
UUCP: pwv@tc.fluke.COM or: { uunet, uw-beaver, sun, microsoft }!fluke!pwv
ARPA: fluke!pwv@uw-beaver.ARPA
"Can't wait until I get the car back into the condition I was
going to disassemble it to"
-TeriAnn J. Wakeman
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