cooling system voltage

[roadrunner1]

a while back there was a thread on how to check cooling system health by using a volt meter to check for milivolts. i have checked a few and have come up with differing results;
the negative lead from the voltmeter was placed on the negative post of the battery, positive lead was placed in coolant.
07 powerstroke -.127 john deere coolgard approx. 16,000 mi. on coolant
06 merc milan +.142 motorcraft gold factory fill 71,xxx
99 mustang -.108 john deere coolgard approx. 28,000 on fill
why am i seeing a negative reading with coolgard and a positive reading with the motorcraft gold?
i also checked a honda crv with unknown coolant or mileage on coolant and came up with a negative number. i remember seeing the graph in the post and anything less than .3 was acceptable but there was no mention of negative readings.

 

[bluestream]

I have no faith in that post about voltage. I checked my BMW that has not had coolant changed to 10 years and got .2V. I bit alarmed I checked my Ford and it was even higher, and I just changed that coolant a few months ago. These numbers have no meaning IMHO

 

[spasm3]

I wonder if you are getting readings that are just leakage to ground. Try measuring other areas than the radiator. It could be also galvanic voltage produced by dissimilar metals.

 

[J. A. Rizzo]

I suspect there can be a huge variability in these numbers depending on coolant chemistry, cooling system metallurgy and metal/metal contact points, meter type and sensitivity, temperature, and probably a host of other things I don't even know about. Yes, there is truth to the notion that corrosion and voltage are correlated, but the factors involved in accurately gauging it via a voltmeter and a dubious grounding scenario renders most simple testing useless IMO. There are more useful things to worry about in the world and on your car than the voltage in your cooling system.

 

[mechanicx]

Are you sure the + lead didn't touch any metal parts in the radiator? It has to be suspended in the coolant.

 

[roadrunner1]

yes, if the positive lead touches anything other than coolant voltage icreases/decreases depending if you had a +/- reading to start with

 

[XS650]

Originally Posted By: Bluestream
I have no faith in that post about voltage. I checked my BMW that has not had coolant changed to 10 years and got .2V. I bit alarmed I checked my Ford and it was even higher, and I just changed that coolant a few months ago. These numbers have no meaning IMHO


http://www.stangnet.com/images/stories/docs/s197_TSBs/06-21-19.pdf

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

http://www.rondavisradiators.com/tech.htm

 

[Craig in Canada]

Originally Posted By: Bluestream
I have no faith in that post about voltage. I checked my BMW that has not had coolant changed to 10 years and got .2V. I bit alarmed I checked my Ford and it was even higher, and I just changed that coolant a few months ago. These numbers have no meaning IMHO


No faith? It isn't a matter of faith. This isn't about "magic voltage" from the coolant - it's about electrolysis. Dirty ground points, poor vehicle design or other factors can result in electricity being forced to take a path through your coolant to complete a circuit. With dissimilar metals in engines you can get severe block or head erosion from the inside out and won't even know it until you take things apart and find a fraction of the metal that should be there. If I can find the links to pictures of thermostat housings that won't seal anymore due to serious electrolysis pitting I'll post them.

Perhaps an important instruction missing from where some people have read about this test is that the engine must be running and all electrical loads on. If you find voltage above a certain threshold you need to find the wiring/grounding problem to stop electricity from flowing through the coolant.

The coolant plays a role in that it is supposed to discourage electrolysis. These properties weaken as it ages, as a general rule. I'm not speaking of any particular type or formulation.

Personally I don't consider this test a coolant test. It's a way of finding an electrical problem with no other symptoms which can cause serious damage to the engine if left unchecked.

 

[mechanicx]

I completely agree. I would just add that even if you don't have a grounding problem or electrical problem, worn out coolant can still show electrolysis. Once the inhibitors and buffers are depleted the coolant stops passivating the metals and can become acidic. And with the dissimilar metals in the cooling system you can have a higher V than .3-.4 V.

There are several tests you can run:
1. Key off, battery leads disconnected and - lead on engine ground.
2. Key off, battery leads connected and neg lead at the battery then engine ground, then chassis.
3. Key on " " all accessory running.
4. while starting
5. engine running and coolant fan on etc.

Let me see if I can find a link.

electrolysis

 

[roadrunner1]

thanks for all of the replys, but i still haven't seen why i have a negative voltage on certain cooling systems.
i have first hand knowledge of electrolysis, having steel boats in fresh water we have to use magnesium to combat the issue. i use coolant test strips and on a couple of engines i send in a coolant anaylsis yearly, but i am still puzzled as to why i can get a negative voltage on one truck and a positive voltage reading on another, is it the coolgard?

 

[onion]

I don't see why it matters.

 

[Ursae_Majoris]

Were your multimeter wires plugged in correctly? Different sign means that electricity flow was reversed.

 

[Craig in Canada]

Originally Posted By: roadrunner1
thanks for all of the replys, but i still haven't seen why i have a negative voltage on certain cooling systems.
i have first hand knowledge of electrolysis, having steel boats in fresh water we have to use magnesium to combat the issue. i use coolant test strips and on a couple of engines i send in a coolant anaylsis yearly, but i am still puzzled as to why i can get a negative voltage on one truck and a positive voltage reading on another, is it the coolgard?


I wonder if the negative voltages you're seeing relative to chassis ground are "natural" or passive eletrolysis (dissimilar metals in an electrolyte - a galvanic reaction) and the positive voltages you're seeing are active electrolysis (improper ground causing electrical system current to travel through the coolant).

Any voltage reading from wiring or grounding issues will be elevated above vehicle chassis ground. There is no electrical system source for any voltage readings below chassis ground other than perhaps some limited use of DC-to-DC converters inside of some components. A galvanic reaction from dissimilar metals, however, is its own "battery" and may read potentials below chassis ground.

Also, the voltages are pretty small if I remember from your first post. Working with sensitive, high impedance, auto-ranging digital multimeters I've seen all kinds of readings induced during measurement from who knows what (induction from other equipment, static charge, dissimilar metals) that you wouldn't even see with a traditional analog voltmeter.

Just spit-balling...