Technical Stray current in coolant

[Foodo]

Doing an oil service today on my 09 MAMY, I noticed the condenser fins were no longer where they should be, and had eroded away. Stray current jumped to mind.

Out with the multi-metre and with the neg in the expansion tank and the pos to the battery I saw 12v running in the coolant. I disconnected the fuses and relays one by one, and then the positive feed from battery to fusebox, this didn't isolate.

There is a further pos feed that goes round the back of the engine to I don't know where, didn't have time to investigate.

Can anyone comment/advise/share on this?

 

[DaveMcT]

The air con condenser is all aluminium. Loss of cooling fins is salt and weathering corrosion simply because the poor thing gets everything thrown at it.

 

[Foodo]

Thanks Dave, thats useful to know. I did think that modern ones were passivated.

I used to work on 100T dump trucks on mines, and when we had rad failures it was invariably due to a stray current. I don't know if Fiat designed the cooling system to include some cathodic protection - I was just surprised to see 12VDC running in the coolant, even when the ignition was switched off.

 

[portland_bill]

The positive cables can only attach to proper feeds that need them, otherwise you'd have a dead short, and either blow fuses or a hot exploding battery. A cable disappearing could be connected to the starter.

There are a number of sensors on the engine, plus the spark plugs if petrol, that use the engine block as part of their earth path. A common situation for over 100 years. There is therefore current running through the engine block on its way to the earth cables. Sticking a multimeter on the block anywhere is likely to show this if the other cable makes a circuit. As coolant conducts electricity, it'll be measurable there too.

I think you're chasing a non-problem. It is just normal age-related corrosion as Dave says.

 

[koalar]

not sure I understand the question. Condenser fins. Jumps to expansion tank


the coolant runs through the engine block which it connected via the gearbox to the battery negative.

I am probably missing something obvious measuring to the positive proves antifreeze is conductive

 

[koalar]

Thanks Dave, thats useful to know. I did think that modern ones were passivated.

I used to work on 100T dump trucks on mines, and when we had rad failures it was invariably due to a stray current. I don't know if Fiat designed the cooling system to include some cathodic protection - I was just surprised to see 12VDC running in the coolant, even when the ignition was switched off.

Aren't you just measuring battery voltage.

the coolant is in the engine which is ground

your other probe is on the positive

isn't it just the same as putting one probe on the minus and the other on the positive ?


I maybe wrong

 

[koalar]

I would have thought a better test would be to put you probe on negative and check the coolant is also at 0V

 

[Foodo]

koalar, dead right - in my haste i wrote the incorrect procedure. :bang:

@ Bill, Love your description of negative earth system, enjoyed reading that. Its a shame I can return the favour and share a URL to what the industrial rad guys say about stray currents in the cooling system. If you are interested, Ipswich rads have a very good article online.

 

[koalar]

koalar, dead right - in my haste i wrote the incorrect procedure. :bang:

@ Bill, Love your description of negative earth system, enjoyed reading that. Its a shame I can return the favour and share a URL to what the industrial rad guys say about stray currents in the cooling system. If you are interested, Ipswich rads have a very good article online.

useful URL added

https://www.ipswichradiators.com.au...tray_current_corrosion_in_cooling_systems.pdf

 

[09 johno]

So fitting and extra earthing strap directly to the radiator will solve the issue, if such an issue really exists!

 

[koalar]

So fitting and extra earthing strap directly to the radiator will solve the issue, if such an issue really exists!

if you had 12v at the coolant you'll have mega problems. Some or all of these and possibly more. Aluminium parts within the coolant would be eaten away in minutes . The battery would have died.The starter motor wouldn't work and possibly wiring melting.

If its a small amount above 0V I guess there would be a problem with the earth strap on the gearbox that's faulty and needs fixing or some antifreeze adding

the battery ground is connected to the gearbox. The engine is connected to the gearbox. The antifreeze is conductive. and connects the radiator to the engine

If the coolant isn't conductive its possible for the radiator itself to measure anything without any problem's its just at a different potential ground. Similar to when you touch something metal and you get a shock

 

[DaveMcT]

A voltmeter has a very high resistance. When connected directly between a battery positive and negative it will show the battery voltage. No harm done but indicates the potential (pressure) available if you connected a normal wire.

Electrolytic corrosion is caused by contact between dissimilar metals in the presence of an electrolyte. This causes a local battery effect and corrosion at the anode. Copper against iron corrodes the iron. Iron against aluminium corrodes the aluminium. Stainless steel against aluminium is especially corrosive to the aluminiumis especially destructive. **

Cooling systems contain an inhibitor which slows the rate of ion exchange. This degrades over time, allowing the coolant to become conductive. This will set off corrosion between the dissimilar metals inside the cooling system. If you are able to see the battery voltage by dipping the voltmeter prod into the coolant it's likely you need to drain and the flush the system and fill with new coolant.

Royal Navy protected it's wooden ships with copper sheathing attached with iron nails, until one ship returned with it's nails rusted away. They discovered the ship yard had removed the protective wax paper from the copper allowing metal to metal contact. Copper nails solved the problem.

 

[koalar]

A voltmeter has a very high resistance. When connected directly between a battery positive and negative it will show the battery voltage. No harm done but indicates the potential (pressure) available if you connected a normal wire.

Electrolytic corrosion is caused by contact between dissimilar metals in the presence of an electrolyte. This causes a local battery effect and corrosion at the anode. Copper against iron corrodes the iron. Iron against aluminium corrodes the aluminium. Stainless steel against aluminium is especially corrosive to the aluminiumis especially destructive. **

Cooling systems contain an inhibitor which slows the rate of ion exchange. This degrades over time, allowing the coolant to become conductive. This will set off corrosion between the dissimilar metals inside the cooling system. If you are able to see the battery voltage by dipping the voltmeter prod into the coolant it's likely you need to drain and the flush the system and fill with new coolant.

Royal Navy protected it's wooden ships with copper sheathing attached with iron nails, until one ship returned with it's nails rusted away. They discovered the ship yard had removed the protective wax paper from the copper allowing metal to metal contact. Copper nails solved the problem.

the original poster was concerned this was happening. The way everything is tied to ground is unlikely.

I should point out a couple of mistakes if you want to experiment yourself

use iron instead of stainless steel. Chromium and lungs don't mix

use bicarb not salt. Chlorine gas isn't great


https://www.youtube.com/watch?v=IjKFE2bKzl0

 

[DaveMcT]

Galvanic corrosion is a battery effect. The noble (cathode) side is not eroded while the anode (base) side is oxidised. Stainless steel is a common problem - only titanium, gold, platinum and graphite sit above it.

All the bad stuff happens to the base metals. Aluminium against stainless is one of the worst because the oxide (Al2O3) is about 2 times the volume of pure metal so its great for seizing threads.