Electrolosis Q's

[3gress]

I'll likely try to isolate the brass fittings from radiator as best as is possible and keep the rad isolated from chassis ground, run corrosion inhibitor coolant with distilled water, and in the absence of finding a two wire coolant temperature sensor with the same characterisitics as OEM sensor, simply clock the dash temp gauge needle to an appropriate degree and pretend it is working! It is not like it gives an accurate reading or indeed warning of impending doom anyway.
I have a modified engine watchdog with engine block mounted thermocouple tied in with a low oil pressure switch to give an early warning of coolant or engine temperature issues and the davies Craig electric water pump controller has it's own warning system so coolant temp gauge is redundant anyway.
An occasional check on stray currents will be employed to keep electrolysis at bay.

Still, those zinc anodes are a small percentage of the cost of radiator plus mods performed on it.

[97 MXV]

Still, those zinc anodes are a small percentage of the cost of radiator plus mods performed on it.

We have now gathered definitive evidence that Zn anodes in an alloy rad would be at best a placebo.

So 3gress have faith and don't believe in the snake oil. Clearly they are not worth tuppence. Stories of Zn anodes rotting out are likely more to do with low PH coolant which is ok for aluminium anyway than anything to do with electrolysis.

Anyway look the cheap alloy radiator anodes come with brass fittings......how hopeless is that ?.......I rest my case.

[3gress]

The problem now is to source a new plug for redundant threaded bung in radiator as the plug previously in-situ was donated to sparkley!

[97 MXV]

The problem now is to source a new plug for redundant threaded bung in radiator as the plug previously in-situ was donated to sparkley!

Sparkley is very grateful for your willing sacrifice.

[Guran]

I'm a Materials Engineer with close to 30 years experience with corrosion of metals. Inevitably I have a few things to add to this discussion!

First thing is terminology. Electrolysis is NOT the issue here. Electrolysis is when a DC electric current is used to drive a chemical reaction. For example water electrolysis is used to split water into hydrogen and oxygen gases. Yes you can use electrical currents to reduce corrosion (cathodic protection) or accelerate corrosion (anodic polarization), but that's not a feasible solution in this scenario.

The phrase you want is galvanic corrosion. This is caused when dissimilar metals are in electrical contact in the presence of an electrolyte (eg. water with dissolved salts). There is an Australian Standard on this (google AS4036) ... some of my lab work from 1989 is in it.

The EMF series gives a rough indication of galvanic susceptibility. However it only indicates thermodynamic trends, does not factor in kinetics (reaction rates) and only applies to pure metals not alloys. A more useful tool is the galvanic series.
https://en.m.wikipedia.org/wiki/Galvanic_series

Unfortunately these tables are specific to the electrolyte considered and only loosely apply to other systems eg. in radiators with glycol, corrosion inhibitors, etc. So treat the published galvanic series as a rough guide for activity vs passivity.

If you're looking to use a sacrificial anode then your best choice would be zinc or magnesium as they're abundant & cheap and very low on the galvanic series. But keep in mind they will sacrifice themselves to protect the less active metals (iron, stainless steel, brass, etc). You need to replace them when they're used up. That's why hotwater systems have a finite life.

There are a few other simple factors to consider. Keep your cathodes small and anodes large. Cathodes are the more noble metals (stainless steel, brass) and anodes are the more active metals (zinc, iron). If you cannot avoid a large cathode then you should coat it to reduce the exposed area that can drive galvanic corrosion of anodic metals.

Next factor is electrical contact. Galvanic corrosion can only happen if anodes and cathodes are in electrically conductive contact, ie. touching. If you can isolate them from each other then you'll eliminate galvanic corrosion. You can achieve this with insulating connections eg. rubber hoses, grommets. The key is to avoid having dissimilar metals, but if they're inevitable then seperate them. That includes isolating from the electrolyte.

Another essential factor is ionic transport via the electrolyte. This closes the electrical circuit in a galvanic reaction as the movement of ions is required to compensate for movements of electrical current. When a car is running, the coolant is constantly flowing in one direction. Galvanic corrosion is unlikely to happen when the car is running because the ions need to move in both directions. So your main concern is when it's stopped.

Aluminium is tricky because it's a very active metal but forms a very protective oxide film and is highly passive and corrosion resistant in most cases. Stainless steel is similar in this regard. Since both need oxygen to work, both are susceptible to pitting and crevice corrosion in areas of differential oxygenation. This tends to occur at joints and laps.

Lastly is the corrosion inhibitor. Cooling systems present a very complex corrosion problem and inhibitors are designed to minimise corrosion issues. Don't skip them.

[3gress]

Nomination for reply post of the year!
Thanks mate for the comprehensive explanation on first what likely issues are to be of concern, and then going on to explain possible solutions.
My main concerns were the different metals reacting, and stray currents in the plumbing increasing the risk of corroding the expensive alloy radiator.
I had assumed a sacrificial zinc or other appropriate alloy anode would help to reduce the radiator degrading, much as in alloy boats using zinc anodes as a form of protection however web searches revealed many conflicting opinions on possible remedies.
Thanks to all replies and the wealth of knowledge graciously offered.

[Lokiel]

Great response Guran.

Will read again!

[97 MXV]

I'm a Materials Engineer with close to 30 years experience with corrosion of metals. Inevitably I have a few things to add to this discussion! There is an Australian Standard on this (google AS4036) ... some of my lab work from 1989 is in it.

Thanks Guran for joining the eggheads and weighing in on a concluding argument to give it heaps more factual perspective.




Below are Lessons 1 to 8 learnt from your input so far and I at least have changed my post title in deference to your input.

First thing is terminology. Electrolysis is NOT the issue here. Electrolysis is when a DC electric current is used to drive a chemical reaction. The phrase you want is galvanic corrosion.

Lesson 1 - Don't neglect proper taxonomy. There were two concerns we spoke about and identified, electrolysis from earth leakage currents and galvanic corrosion...clearly they need to be explicitly differentiated.

The EMF series gives a rough indication of galvanic susceptibility. However it only indicates thermodynamic trends, does not factor in kinetics (reaction rates) and only applies to pure metals not alloys. A more useful tool is the galvanic series....treat as a rough guide for activity vs passivity.
https://en.m.wikipedia.org/wiki/Galvanic_series

Lesson 2 - Use proper Galvanic Series not EMF Series. This particular Galvanic Series for metals in stagnant sea water rough guide, like AS4036 means maybe the significance of zinc anodes in aluminium radiators swimming in coolant containing inhibitors might differ by orders of magnitude, but like EMF it does suggest Magnesium anodes are a better choice than zinc if belt and braces technology embraced.

Keep your cathodes small and anodes large. Cathodes are the more noble metals (stainless steel, brass) and anodes are the more active metals (zinc, iron). If you cannot avoid a large cathode then you should coat it to reduce the exposed area that can drive galvanic corrosion of anodic metals...zinc or magnesium...they will sacrifice themselves to protect the less active metals (iron, stainless steel, brass, etc)

Lesson 3 - This lesson sounds like a copper pipe/brass fitting cathode vs zinc anode in hot water system perfectly explained.

Keep your cathodes small and anodes large. Cathodes are the more noble metals (stainless steel, brass) and anodes are the more active metals (zinc, iron). If you cannot avoid a large cathode then you should coat it to reduce the exposed area that can drive galvanic corrosion of anodic metals...

Lesson 4 - This lesson sounds like an alloy radiator/brass fitting cathode vs zinc anode in proper coolant system not perfectly explained.

Next factor is electrical contact. Galvanic corrosion can only happen if anodes and cathodes are in electrically conductive contact, ie. touching. If you can isolate them from each other then you'll eliminate galvanic corrosion. You can achieve this with insulating connections eg. rubber hoses, grommets. The key is to avoid having dissimilar metals, but if they're inevitable then separate them. That includes isolating from the electrolyte.

Lesson 5 - This lesson seems to make the case for an aluminium radiator with plastic tanks (like OEM) or for keeping electrical brass fittings separated entirely or at least keeping them dry.

Another essential factor is ionic transport via the electrolyte. This closes the electrical circuit in a galvanic reaction as the movement of ions is required to compensate for movements of electrical current. When a car is running, the coolant is constantly flowing in one direction. Galvanic corrosion is unlikely to happen when the car is running because the ions need to move in both directions. So your main concern is when it's stopped.

Lesson 6 - Very interesting that 3gress can heed this lesson by keeping his electric water pump going 24/7 perhaps

Aluminium is tricky because it's a very active metal but forms a very protective oxide film and is highly passive and corrosion resistant in most cases. Stainless steel is similar in this regard. Since both need oxygen to work, both are susceptible to pitting and crevice corrosion in areas of differential oxygenation. This tends to occur at joints and laps.

Lesson 7 - This lesson begs the question...Why not forget dubious cathodic protection ?...loss of oxide layer protection sounds like the real issue.

Lastly is the corrosion inhibitor. Cooling systems present a very complex corrosion problem and inhibitors are designed to minimise corrosion issues.

Lesson 8 - This lesson begs the question...Why not forget dubious cathodic protection ?...loss of coolant effectiveness sounds like the real issue.

Seems to me the only thing missing is to establish levels of significance to the competing mechanisms explained in the context of a detailed System Description including functional and detailed specifications of what might now might be actually proposed.
Is that something you might like to offer up at some stage 3gress ?
(Knowing how much I love zinc anodes.)

[3gress]

You are assuming first that i finish putting the car back together and second am in a physical state to drive it!
The probability that i can actually drive it for any reasonable length of time, enough for radiator corrosion in any form to be of concern, is so small that it should be placed way further down the list of nightmare fodder.
How I'm going to manage the clutch with dodgy knees should warrant more attention, coilovers and fixed back bucket seats more so!!!

White paper time Keith

[97 MXV]

radiator corrosion in any form to be of concern, is so small that it should be placed way further down the list of nightmare fodder.
How I'm going to manage the clutch with dodgy knees should warrant more attention, coilovers and fixed back bucket seats more so!!!
White paper time Keith

Given your expressed need Dan, the least I can do is start with research on coolant from its origins, beginning with the scientific premise that Life on Earth evolved from the sea.
Therefore coolant having its primitive origins in sea water has thus evolved over the eons into today's modern high tech coolant as the lifeblood for the modern alloy radiator containing "antibodies" protecting it from corrosion and pure water to help transfer the heat.
My friends at Penrite were good enough to whip this preliminary white paper together to begin to demonstrate that coolants ain't coolants.

The thrust of that Penrite white paper seems to indicate the need for the right coolant type and regular coolant testing.

Looking at coolant properties, I would further suggest that your large radiator size and large fans for an atmocharged engine together with high coolant flow rates possible with your electric water pump, means that you may not need much pure water (high specific heat value) in your coolant for cooling effectiveness using a lower specific heat coolant (pure ethylene glycol) based on a time differential of this fundamental formula.



I am not sure but imagine that elimination of water from your coolant (if possible) might also be a good way of eliminating galvanic corrosion and electrolysis based on the enlightening insight provided by Guran.

[lonesailor]

Using distilled water with the coolant is important when considering galvanic corrosion. Many years ago I got caught out using floatless level controls, which rely on the conductivity of the liquid to operate, in a steam condensate return system in a factory. It worked fine on startup then failed. Turned out that as the condensate became pure,i.e the water became distilled, the conductivity of the water became so low as to prevent the system from working. We had to retro fit float switches. No current flow,no galvanic corrosion.