If you ever wondered what eles you can do with your volt meter I found this articile while looking for something else; you can use your voltmeter to test your engine coolant.
http://www.cadillacforums.com/forums/cadillac-forum/t-60843.html

mcowden
12-22-05, 01:47 AM
Antifreeze Analysis

In stead of using a coolant test strip:
“You can also use an ordinary digital volt meter for the same purpose. With the engine off, touch the voltmeter positive test lead to the radiator or engine (making sure you get good metal-to-metal contact). Then open the radiator cap and insert the negative test lead into the coolant. A reading of up to 0.2 volts is considered acceptable and indicates the presence of reserve alkalinity in the coolant. If the coolant reads 0.3 to 0.6 volts, it is borderline and should be recycled or replaced. A reading of 0.7 volts or more would tell you the coolant is overdue for a change.
Internal corrosion in the cooling system can occur regardless of the condition of the coolant if voltage from various accessories (alternator, starter, ignition, etc.) flows through the coolant to ground rather than follows the intended ground path through the ground strap between the engine and chassis or the ground cable between the engine and battery. You can check for this condition by also using your DVOM. Use the same hookups as before to measure the voltage of the coolant, but this time while cranking the engine, then with the engine running and lights and heater on. If stray current is grounding through the coolant, you'll get a voltage reading. More than 0.15 volts can corrode aluminum, and 0.3 volts can be harmful to cast iron. Check, clean and tighten the ground straps and/or battery ground connection to eliminate the problem.”

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84 300D, 82 Volvo 244Gl Diesel

Pretty important for Cadillacs considering they use Death-Cool.

Hi.

When i checked the coolant with that method,i read 0.7V at the voltmeter,but during 10 second after,the voltage,gradually,went down to 0.1V.
Should it needs to stay on 0.7V in order to identified as a problem?
Since in my case it didn't stay on 0.7V,it was 0.7v for 2 seconds and started to decrease,gradually, to 0.1V?
What is it mean?
Thanks in advance.

An automotive radiator IS a battery with the coolant acting as the electrolyte. The acidity of the coolant is reflected in the radiator's ability to store current just like the lead-acid battery used by the electrical system. I hadn't seen the voltage values listed but certainly can't disagree with them. I've always looked for very low voltage values and have actually seen a couple of systems that would light a 12V test light (not common).

If you're getting a bit of voltage that dissipates in a short time I'm inclined to think that the radiator isn't grounded (most ground thru the attachment bolts) so it's acting like a capacitor and temporarily holding power though I'll have to think about this a bit more (scratching head.....).

Dan

Your results will vary because of the input impedance of the meter. Since you are basically checking a capacitor by using two electrodes and electrolyte, a higher impedance meter will give you higher readings. The issue is coming up with a voltage "standard" without using input impedance ratings.

It is the same concept as a "lemon battery" or "potato battery".

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Sam

84 300SD 350K+ miles ( Blue Belle )

But what does my results mean?
Is the decreasing of the voltage from 0.7v to 0.1v means that the coolant is good?
while it should stay constantly on 0.7v in order to show that it is not good?

In a word....nothing. It's a nice idea but as I mentioned, without knowing the impedance rating of the meter, and using a comparable unit, you are just seeing "something". Sure the idea may help in troubleshooting a problem but trying to rely on any kind of accuracy is quite a stretch.

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Sam

84 300SD 350K+ miles ( Blue Belle )

I really confused
All the articles that i read through the net show exactly the same method and the same value:0.0v-0.2v=good/0.3v-0.6v=need a change/>0.7v=must be changed.
Even in this thread,i see the same method and value and now you said that it means nothing.
The problem that in all the articles they don't mention if the value should be steady.They only mentions the voltage value.
The issue is not the accuracy,the issue is if the voltage value should be steady or not?

I don't see why the test is compared with a capacitor. You have an electrolytic (galvanic) cell. One electrode is the metal parts of the radiator itself. The coolant is the electrolyte and the voltmeter probe that dips into coolant is the other electrode.

There are other variables, like the metal the rad and the probe are made from and the coolant composition that could affect voltage.

There is a ton of stuff on the internet about using this method. 0.3V is the magic number, it seems. You should be below that (I think this assumes aluminum rad)

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

"...voltage from various accessories (alternator, starter, ignition, etc.) flows through the coolant ..."

Nonsense.

I would like to mention that my main question is:
Does the gradually decreasing of the voltage(during 10 sec) in the voltmeter from 0.7v to 0.1v(while making the test) mean that the coolant is good?
while only if the voltage value stay steady 0.7v(in the votmeter),just then,it will show that the coolant is not good?

I just measured my 300D and the VW and the voltage also dropped slowly on both like yours till it stabilized to around 0.1 V. I know my coolant is good they were both recently changed. Neither radiator is grounded to the chassis. Are radiators supposed to be grounded? I do not see a radiator ground strap on neither car. I also used 3 different DVM's (2 HF's) and the readings were close on 2 of them. On one of the HF where I changed the probe tips to alligator clips (looks like shiny tin plated) the voltage was much higher (started at 0.3 V and dropped slowly). I think the material of the probe that touches the coolant matters in what voltage you get.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I think what was meant was sneak path through the coolant to ground due to bad main ground, not the entire current from the accessories going through the coolant. I've had a very loose ground strap which caused my instrument cluster trace to burn out while trying to repeatedly start the engine, which just clicked. Same phenomenom.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I would think that the initial value is the more accurate number. Or better still, the one with engine running.

There could be a number of reasons for the voltage to drop. Gas forming on electrode, corrosion inhibitors doing their job, passivation of the electrode.

One thing to consider, is that there is a difference between straight old 50/50 Ethylene glycol coolant and the modern G05 and Dexcool coolants. The latter are designed to be more acidic than the old types. Do any of those article suggesting 0.3V say what type of coolant and which rad/probe metals that applies to?

I don't see any good way of determining the corrosion protection of coolants. I doubt test strips would handle all types of coolant. The freeze protection can be checked with a refractometer or hydrometer, but neither are very accurate.

Best solution may be to just change coolant on schedule recommended by engine manufacturer or coolant manufacturer.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Those match instructions that came with a new heater core for a Ford truck. Measurements < .3 volts are considered ok. Anything over and the coolant needs to be changed. Supposedly electrolysis takes over at .3 volts.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.