Galvanic corrosion in glycol solution

[TChronos]

I'm designing a thermoswitch adapter that will be used to control an electric fan in automobiles. The adapter mounts in a header tank, which can be steel, aluminum, or brass depending on model and vintage. The switches are always brass cased, and screw into the adapter.

The adapter is (or should be) immersed in a 50/50 antifreeze mix when the motor is hot, but can be exposed to air when the motor cools. At this point, my thinking is that brass would be the best material for the adapter, since it's important that the switch not corrode to the adapter. But if the tank is aluminum, would I be causing damage elsewhere? I can only choose aluminum or brass for the adapter.

 

[rnd2]

The last time I looked Glycol is not conductive. As long as your liquid is not an electrolyte galvanic corrosion is not an issue. Check the electrical properties of your liquid; particularly insulation resistance.

 

[moltenmetal]

50/50 glycol/water is most certainly conductive. Typical automotive antifreeze mixtures are heavily laden with corrosion inhibitors to deal with the many galvanic couples found in the coolant system. As to the correct choice of material in this application, I'll leave that to others here who are far more knowledgeable than I am.

 

[rnd2]

Source:

http://downloads.pennnet.com/pnet/misc/sst/tuma.pdf

"The best attainable resistivities for DI water and DI/glycol are about 107 and 108 ohm-cm, respectively. The resistivity of DI/glycol fluids can degrade quickly if the deionizing bed is not
properly maintained or if the fluid is spilled. The dielectric constants of ethylene glycol and water are 38 and 78, respectively [13], at 25°C."

 

[Metalguy]

Since the switch must be easily removable, use a brass adapter. Any galv. corr. would then be in the alum. closest to the adapter, *if* the owner lets the corrosion inhibitors get depleted.