Yes, very true, but since we are talking about a radiator, I decided not to mention that, unless you some how short an ignition coil to you raditor...

 

I don't think he was saying that air is not conductive. and last I checked coolant didn't have "air" floating around in it. I think his post was more to refute the inaccuracies stated by the OP's mechanic. so let's keep the discussions to things only relevant to this thread. adding more info than is needed will only confuse the matter.

 

Yes and no...

Going back to my bunch of small wires on the ground example, making those small wire close together does not make the air more conductive. It does, however cause a lowering of activation energy, or spark energy. In other words it becomes easier (read less voltage) to jump electron from one wire to the next. But in the voltage range that this meter is applying and reading, you could just set one wire on Earth and the other Saturn and it probably wouldn't make a difference.

The problem is this, in one case we are measuring ionic conductivity (the ethylene glycol breaking down) and in the other case electronic conductivity. Obviously electronic conductivity is dealing with electrons moving around. Ionic conductivity is not actually dealing with electrons, but rather ions. Ions are charged particles, they have extra electrons or are missing electrons, but in general they are not moving electrons from point A to B as in electronic conductivity. So in one case entire molecules are being measured and one case just electron are being measured, they can't actually "help" each other out because they are different units altogether, if that makes sense.

 

Here's my 02$ FWIW

I have worked on many boilers that have conductivity measurement of the water in the steam drum. This conductivity measurement is used to control blowdown rate and chemical injection rates.

While pure (distilled) water is non-conductive (infinite resistance), it becomes increasingly conductive (less resistance) as it gets saltier. Another point is conductivity = 1/ resistance (inverse).

Since the conductivity of the water does climb as salts get concentrated in the water, this is a big deal in a boiler. Because the steam leaving the drum is 100% pure distilled water vapor, but the feedwater coming into the drum is just treated water, with impurities, salts, sediment, etc.

So the sediments steadily feed into the drum, but only water vapor leaves. This tends to concentrate the sediments in the steam drum. As the salt concentration increases, the conductivity goes up. So you have to blow down (waste) a certain percentage of water in the steam drum just to flush out the salts and sediment.

So while the idea of checking conductivity seems sound at first glance, there are a few things that bother me about the mechanics test.

First, the auto cooling system is a closed loop. So unless you are consistently topping off the overflow tank with water from the tap or garden hose (NONO), then you are not adding more salts or sediments. Whatever exists in the auto cooling system is trapped. The only source (if you are topping off with distilled water) of sediment would have to be due to corrosion/oxidation of the metal in the system. Beyond me.

The biggest problem I see is that the units for conductivity are micromho's (inverse of micro-ohms) or micro-siemens. I don't know how the mechanic correlated the 0.4 volt reading back to conductivity. Come to think of it, that voltage reading is just noise anyway. I bet if he used an analog meter (they have a higher input resistance) then he would have read 0.0 Volts. Even if the coolant has gotten conductive, it doesn't generate power. There is nothing to generate the 0.4 volts. On a volt meter, neither lead is powered. And metal particles and salt cannot generate electrical power either.

On the other hand, if he had checked with an ohm-meter, and gotten a resistance measurement in ohms, you at least are dealing with the correct units (after inverting) and therefore the correct (electrochemical) phenomenon.

If he had used an ohm-meter, the red meter lead supplies the power for the loop, current is regulated by the resistance of whatever load you connect beween it and the other black meter lead.

 

Isn't resistance measured in ohms and conductivity in mhos. You have to apply a voltage to get those measurements. Like snakeeater, I believe trying to measure voltage across a pool of coolant is ridiculous. Perhaps engine coolant is the latest and greatest in battery technology.

 

it really isn't that ridiculous to measure it in volts. An ohm meter or multi meter applies a known current to what ever and then find the voltage drop (a current accross a resistance will cause a drop in voltage which can be esily measured). From there most multi-meter or conductance devices apply Ohm's law, V=IR rearranged into R=V/I where R is the resistance, V is the voltage drop and I is current. It is extrememly hard to measure resistance directly, so this indirect method is applied to almost every thing that measures resistance. So you can indeed get conductivity from volts, but it is very strange and I have never seen it done that way, and I deal with conductivity of some weird materials almost daily, but the theory still works, strange as it is.

As for the slat thing... when salt is in water it breaks down, for instance NaCl (table salt) breaks down in Na+ and Cl-, this goes back to what I said that metal ion can indeed make a solution more conductive. When ethylene glycol breaks down it is this very same thing that is making the solution conductive, like I said earlier OH- ions can make a solution conductive, both of these are case of ionic conduction.

 

"Conductivity" should be relative to the amount of electrolytes in solution. As far as OH- or H+ in solution, this is no different than measuring pH. A pH meter is just a conductivity meter, but the readout is in different units.
Conductivity of an engine coolant can vary depending upon the type of additives in the coolant or the amount of metal sloughing off into solution. In our case, this would be mostly aluminum and lots of rubber paricles. As such, I don't consider conductivity as a good indicator of engine coolant life (or what life remains).

 

^^jrfish did say that in one of his previous posts up there.

 

Yes, that is what I getting at, they are really just measuring pH, not electrical conductivity. Pure ground state metal particles will not effect the pH though, if they are in ion for they may, but I'm doubtful that there are ions floating around inside the raditor.