At last, a "roadster" subject that I'm qualified to talk about!!!
"The mechanic I mentioned suggested putting a small block of magnesium in the
trunk would work (outta sight)."
"No, just putting a chunk of magnesium in the trunk would not work. There has
to be an electrical connection between the sacrificial metal (magnesium or
zinc) and the metal to be protected. There ALSO must be a medium through which
the molecules of the sacrificial metal can move to the area of
corrosion. With marine application the "zincs" (as they are called) are
connected to the part to be protected and the medium for movement is the sea
water. In a radiator, it's the coolant, I suppose. This is an
electrical/chemical phenomenon, and you must have a complete circuit."
Yup, it's true. The "medium" mentioned above would actually be termed the
electrolyte, and the coolant works OK as an electrolyte. Any time there are
two dissamilar metals in contact, there is a weak electric current generated.
The galvanic potential between the two metals can vary depending on the metal.
Magnesium and alloys of magnesium are at one end of the galvanic scale; this
means they are anodic, or least noble. Zinc is next in line, and has the
advantage of being much less expensive. That's why so much steel is
"galvanized" which is really just a zinc plating or dip. The zinc acts as a
sacrificial metal and corrodes away first; when the zinc is depleted the steel
will begin to rust.
If you look at the galvanic scale you will see that certain aluminum alloys and
steel and cast iron are right next to each other on the scale, meaning that the
actual galvanic potential is pretty low. If they were farther apart, the
potential would be high enough that they probably wouldn't be able to mix
alumium heads with cast iron blocks. Of course, the higher the temperature
that the metals are subjected to the higher the galvanic current is generated.
That's how a thermocouple (like the one in your gas furnace or water heater)
works.
I personally don't know if I'd bother hanging an anode off the radiator cap,
since it would work much more effectively bonded tightly to the metal I wanted
to protect. I also doubt that it would help with head corrosion, but it might
protect the radiator a little bit. Others would be more qualified to talk
about the necessity of chaning your coolant on a regular basis, which can do a
lot to protect your radiator...
Fred Johnson
'69 SRL 009546 with the highly preferred teardrop side marker lights and high
windshield and sideways radio and.....still in pieces - but my wife's given me
the OK to start spending money on mine again! Hope to get the engine and
transmission done this spring/summer!
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