galvanic corrosion in automotive coolant system

[will123123]

I have been having some issues with galvanic corrosion in a coolant system of a race car (operating at approx. 120°C and 4bar), this causes problems of increasing coolant pressure due to the production of hydrogen gas in the system (accumulated gas made a pop sound when touched with a lighted match). The radiators are aluminium and there are other materials including steel in the system and a potential difference have been measured between different parts of the system. My next step is to get the coolant analysed for aluminium content after use to confirm whether it is the radiators corroding.

Changes to different coolant additives have not been successful. My colleagues are now keen to place 'earthing' straps between the different areas, however I not believe improving conductivity is the correct approach and in reality the opposite should be done, ie isolate each area.

Advice on the best way to go would be appreciated, as would any other ideas or comments.

 

[btrueblood]

Grounding straps would seem to be in order, if you are generating sufficient current to generate hydrogen gas.

 

[EdStainless]

The ground straps will help by reducing the electrical control between the metals on the inside of the system.
Have you looked at molybdate inhibitors? They are the least environmentally sensitive ones out there but they are very good in mixed metal systems.

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Plymouth Tube

 

[CoryPad]

Coat the cathodic materials (e.g. steel), it will have a bigger influence than coating the aluminium.

 

[SJones]

How were the potentials measured and were they measured from the outside by any chance? Look at the coolant formulation and assess whether the hydrogen could have come from degradation of the constituent chemicals. If all else fails, why not connect the radiator to the rest of the system via non-metallic, sheathed hoses (like a normal car!) - that should sort it.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[blacksmith37]

By "steel" I presume you mean cast iron; A great many autos use the aluminum/cast iron and commercial inhibitor/glycol systems with no corrosion problems. What can be different about yours? As previously suggested; I would concentrate on the inhibitor.
Over many years, the only galvanic problem I have seen is when the idiots at GM put on small aluminum fitting (intake manifold, water out ,elbow) into a system that was otherwise all cast iron /copper.

 

[will123123]

Thank you for the replies so far. Initially we ran a water additive recommended by the engine manufacturer, but that was not successful. We have now tried with using distilled water only and this proved much better - ie minimal pressure build up. We are going to keep monitoring using this for the time being.

 

[EdStainless]

You need to add something to the water, if not the inhibitor then at least some ethylene glycol in order to raise the boiling point.

Are you using a commercial coolant? (Prestone II) If not, then why not?

My hunch is that this system has some different metals connected to each other that they cannot avoid. Isolating each metal from the others will keep this from happening.

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Plymouth Tube

 

[tnatale]

Normally the coolant in those types of systems are a mixture on inhibitors in a water/glycol vehicle. A mixture is necessary because of the wide variety of metals typically involved in the cooling system, Al, Cu, steel, cast iron. As would be expected, inhibitors that work for one metal may not work for another. Modern formulations contain things like silicates, triazoles, molybdates, etc.

You're going to have significant corrosion problems if you don't have an inhibitor package. I'd go to some of the coolant companies and see if they have a specialty high temp/performance version of their product.