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Discussion Starter #1
I dug up some old threads where someone mentioned using a voltmeter to measure the voltage produced in the coolant system, and to use the measurement as a way of telling how much damage (galvanic action?) was going on in the cooling system. A DC voltage of over 0.50 volts was a sign that the coolant should be changed. They called it "EME" measurement.

http://www.z06vette.com/forums/showthread.php?t=69411&highlight=EME

http://www.z06vette.com/forums/showthread.php?t=7250&highlight=EME

Anyway, I checked the EME level on my Zee with an expensive Tektronics TX3 DMM (Digital Volt Meter) and got around 120 mV (0.12 V). You will get a positive voltage reading when the voltmeter's + probe is on the engine head and the - probe in the coolant. You get a negative voltage reading when the - probe is on the engine and the + probe in the coolant. The voltage reading would float around some, but seemed to be around 120 mV.

Then I tried the same measurement on my truck. The voltmeter reading seemed to float around much more. When the measurement was first taken, it would read about 120 mV, but if I just watched the reading for awhile it would decrease down to about 30 mV and stabilize. If I reverse the leads it would start high again and come back down. So, I'm assuming that an accurate reading is when it's stabilized and not the initial reading?

Anyway, just trying to understand what this EME test is really telling me. Is there anyone out there who can explain exactly what's going on when with this test?

Thanks
:cheers:
 

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:jawdrop: Someone during one of the battery threads in the last day or two stated C5's have a current draw of some value. Don't remember how much it was but it can draw down your battery if it''s not charged. It looks like you are reading the conductivity of the coolant. Maybe? Or you may be reading a floating ground. Switch your VOM over to Ohms and see what you get. Do the truck too. This is interesting!!!!!!!!!! Try changing the grounding points and see what happens.

D.J.
 

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Discussion Starter #3 (Edited)
I've done a lot of parasitic current draw measurements on the battery. The C5 Vette will draw 18 to 20 mA of current when sitting in the garage. It would take about 2 months to discharge a healthy, fully charged battery with this amount of draw.

In those threads I listed in my first post, they say the EME voltage is produced by the reaction between the coolant and engine metal. It is like it's own battery source. It is not the current draw on the battery I described above. The EME level gets higher and higher when the coolant becomes old and worn out.

I'm just trying to determine how to accurately measure it, and exactly how there is a voltage produced from the reaction between the coolant and engine metals.
 

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I guess that's what I was trying to say. You would be measuring the conductivity of the coolant. Where the coolant would become more or less conductive as it ages. As I'm sure you are aware, galvanic corrosion happens with two dissimilar metals are present. I'm going back really far now, (early stages of My life). The two metals form a battery that generate a voltage. The coolant in this case would be the dielectric needed to form the battery or capacitor. The various metals that are in an engine will give themselves up over time and some may make the coolant more or less conductive. Boy does this sound like a lot of B.S. I'm sure this is a topic of someone's masters. When you place your probe into the coolant and connect the other end to the head bolt, (ground) you are measuring the conductivity of the coolant. Beware that I may be bordering on the fringes of science here. I'm just recalling the theory of a battery and galvanic corrosion. I'm sure if I am wrong someone will step up to the plate and correct me. A little knowledge is a dangerous thing.

D.J.
 
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