Voltage in Radiator Coolant

[PhilM]

I've been trying to get my MSPnP to stay tuned - so I ran another earth around all the engine earthing and back to the CPU.
I decided to check the coolant in the aluminium radiator for voltage and got 0.5V. disconnected the battery and it gave the same reading. Fitted an earth to the radiator - same reading. I took some coolant out and put it in a clean old aluminium saucepan an still got a 0.3 v reading.
Its a well known coolant concentrate in the right dilution with demin water - only 6 months old, in a new radiator and reconditioned clean internals engine.
I sent the coolant manufacturer an inquiry via their website on wed but have had no reply.
Anyone measured for stray voltages?

[gslender]

You're seeing the electrochemical reaction that would be common in old cars with old cooling systems. Definitely change/flush the cooling system and move on.

[sailaholic]

Your always going to have a voltage. Where you are placing your probes, what the probes are made out of and what the container your using (sauce pan, block, head) will change that reading.

It's not just about old cars, it's chemistry. Some things are more active then others, there for a voltage will exist. "Ground" can be very confusing here to conventional electrical knowledge.


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[gslender]

My point was that older cars tend to have more of that chemical reaction occurring - when too great, it will be a sign of fast corrosion and you need to flush more frequently


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[sailaholic]

Electrochemical potential isn't a sign of corrosion, only a potential difference between materials that can result in corrosion under the right conditions. Current flow in the corrosion circuit is the measurement of something happening.

The measurements can't be said to have relationship to the presence of corrosion, at this stage we don't even know if the measurements made were within a single corrosion cell.

Any engine which used mixed metals in in the cooling system (aluminium, steel, brass and iron in a bp at a guess) will have a an electrochemical potential to anything else. What the potential is will depend on what the reference point is.

Corrosion will occur to the most active metal in a physical position to influence the reaction (not the most active metal in the system) but is dependant on the ph, conductivity, presence of corrosion inhibitors, oxygen etc.


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[gslender]

So why is the common advice to measure and flush coolant fluids, blaming old coolant as being the reason - or is that method, in your opinion false?


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[sailaholic]

False method if the are saying to measure potential of the coolant in my opinion. There may be some method to it but it would need to be a lot more specific about how you do it.

My day job is to protect buried transmission gas pipes from corrosion. Natural Steel in soil has a potential of -550mv on average against a copper rod immersed in a saturated copper sulphate solution. This is called a Copper/copper sulphate reference cell.

If we measured the pipe against say an electrical earth grid in soil we would probably get a result of -350 millivolts (roughly it's a far less stable reference).

Against a zinc reference cell (treated block of zinc) the potential of steel would be about +500mV.

We can stop the pipes corroding (in a basic general sense) by pushing the potential 300mV more negative. Ie from -550mV to -850 mV against a copper / copper sulphate reference cell.

How much current we need to do that depends on soil conditions and quality of the coating (which breaks the conductive link of the soil). Current demand can be between 2mA and over 1000 amps.


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[PhilM]

Thanks for the discussion
The reading was done using a Digitech multi meter the -ve probe pushed on the aluminium neck of the radiator/saucepan and the +ve probe held in the coolant not touching any metal. I just had a look at the probes they appear to be chromed copper as the +ve probe has the chrome worn/corroded off it which cause a potential.
My B6 engine should be considered only 6 months old as the block was hot washed and degreased several times the new Al radiator only fitted 3 months ago. The heater was the only original part and it had been flushed several times.

I am considering using a product called Inter-ject Electrolysis Arrest it was recommended by a local mechanic/restorer, after I do a flush and add new coolant/demin water.

When I get a chance I am going to put some new coolant diluted correctly with demin water, in the sauce pan, then test tap water and then demin water to see what the potentials are.
There is an opinion that says demin water is too ion hungry so tap water should be used - but commercial premix coolant is mixed with demin water.

My Mech Engineering chemistry was 40 years ago, but a half volt potential did not sound right. In powerstations most of the heat exchangers/closed circuit coolers, use deminwater and they last for 30 years.

Yep I could just change it and move on but the hours I have spent on this bloody car trying to get it right I didn't want a new radiator corroding out before it should adding to the problems.

[sailaholic]

I'd definitely be going the demin water.


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