Hey guys and gals,

While reading about electrolysis in cooling systems I dunked my multimeter probe into the expansion tank and put the negative terminal on the neg battery cable. Negative .25 V. It should be 0, or so Im told. This is with the key off, car having just been run. My coolant is Zerex G-05 50/50 with distilled water, and was completely flushed 9 months ago.

I then:
- dismantled and cleaned the battery posts, battery ground cable, and ground strap. Sanded all and coated with dielectric grease. No change in voltage.

- I removed the positive battery lead and re-checked. No change.

- 0V between engine and chassis ground. 0V between negative battery cable and chassis ground. 0V between engine and chassis ground.

Meter is a Fluke 289, in good working order, and Im well versed in its use.

Can someone clue me in as to what to do next or something to check?

dd

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

Next, stick your probes in a grapefruit.

stick both probes in the coolant.. .what do you get?

buy a piece of litmus paper, dip it in your coolant.


how do you get negative voltage?

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did you use distilled water?

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I just did the same thing.

Key-on vs. Key-off did not have much effect.

.20 vs. .19


both probes in coolant = .03 and slowly dropping

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That's bad. It means you are eating away at your radiator and heater core supposedly. Usually it means your coolant needs changing. My problem is my coolant is new.

With both probes in the coolant you aren't measuring anything, the coolant is all at the same potential.

I did use distilled water by the way.

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

http://www.awrracing.com/media/electrolysis.pdf

page 2 , top right.

You have a cast iron engine.... you're fine.

if you have an aluminum head, these numbers could mean trouble.

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http://www.awrracing.com/media/electrolysis.pdf

same numbers here as well

under .3 V is good to go.

Thanks for bringing this to attention. I was not aware of this.

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http://www.wjwatson.com/coolingsystem.php

same numbers. anything under .3 V is ok.

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What about my radiator and heater core?

And how can I get negative values?

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

I'm also curious about this. The articles trying to sell something make it clear there is a problem with those voltages.... otherwise, there is little mention.


I am going to pull fuses one by one and look for changes... if there are none, I'll be plenty happy.

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Just pull the positive battery lead. Thats like pulling the whole fusebox, right?

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

test from your engine block to your radiator.... what do you get?

The system is inherently a battery due to the nature b/w iron an Aluminum.


If you battery is disconnected, where is the "electrical leak' , that you think you have, coming from?

If I put a rotor and an intake manifold in a bath of water and check the electric potential, what will I get?

However, if those parts are touching in the bath, it might not be the same. Like your aluminum t-stat housing tested with your iron engine block...

Blame Mercedes for mixing aluminum and Iron... not your electrical system.

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by switching leads or adding a power source.

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there were minor changes pulling the fuses individually, nothing I could remember.

Once I pulled the battery and Voltage remained the same, I tested the radiator fins to battery Neg. = 0.4

Then it made sense.

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The result is more about what the end of the probe on yout multi meter is made of. You had electrolysis, one of the electrodes was your probe. Any smart college student doing chemistry can explain how the voltage comes about. If you swap the probes, you will get a +ve voltage. As soon as you have 2 different metals place in a solution and connected you have a voltage. What is important is how much current flows. The coolant contains chemicals that coat the surfaces over time and reduce corrosion. Its not a good idea to keep on changeing what brand of coolant you use. Get a good one & stick with it.