Radiator Anodes: needed?
 

I was reading Codrus' build thread, and he mentioned a radiator cap anode.

I've not seen corrosion on well-maintained coolant systems.

Should we be concerned with cathodic protection of coolant parts? If so, what is the best method?

I'm kinda curious on other people's thoughts on this as well.

I always thought an anode would only do good in electrolysis, as some cars (ford, mostly?) like to eat the radiators from the inside. The anode is supposed to be a more reactive metal, so it is the sacrificial point of least resistance.

Stock miata radiators seem to last till the tanks blow up, no matter how they are maintained, so I'm not sure our cars were ever set up so electrolysis was a problem. I don't really see an anode doing any good, in other words.

With a all aluminum radiator instead of the plastic one though, maybe? Though the stock one isn't exactly electrically isolated it is a lot more so than an aluminum one.

Galvanic corrosion happens when you have two dissimilar metals in electrical contact with each other in the presence of an electrolyte. The greater the difference in the electronegativity potential of the two metals, the faster it corrodes. The canonical case is an iron and copper pipes/fittings screwed to each other with water flowing through them.

Galvanic corrosion - Wikipedia, the free encyclopedia

The block is iron, the head is aluminum, and the coolant is an electrolyte. That said, I dunno if having an anode in the radiator is useful or not, because I would have thought that the rubber mounts would prevent electrical conductivity between the radiator and the block. OTOH, the sacrificial anode that comes attached to the radiator cap in the TSE radiator has noticeably reduced in size, so... :)

--Ian

Ideally, you'd want magnesium.

There will always be some voltage in the cooling system, no matter how well you isolate everything. The typical max is 0.3v measured from the liquid at the cap to a chassis ground. Anything more than that and you're going to have a bad day. Even with low system voltage, however, the anode is a good idea, and it's a very good idea if you are running little or no coolant in the system (because race car).

Because of the lack of corrosion inhibitors that are supplied in the coolant?

True. Zn is between Al and Fe, Mg is above Al.

My PWR aluminium rad is eating away - unfortunately the PO didn't change the coolant enough and there is definitely significant corrosion occurring, it is eating away the radiator hose flanges in particular. Regular coolant changes since I bought the car have slowed the process but I would really like to use an anode.

Is there a commonly available rad cap that has an anode and will fit the PWR? I think the cap is the same as the standard Miata rad...

I have also had someone suggest earthing the rad using a wire from the rad to the chassis... Any value in doing this?

That, and the coolant acts as an anode itself.