One other thing you need to watch out for is that the sacrificial material in
the reaction can sometimes be the coolant hoses themselves. I have seen a few
hoses suffer from ECD (electrochemical degradation). They get soft and have
what look like cuts on the inside of the hose. You can feel a hose that suffers
from ECD just by squeezing it. Usually it will be close to one end. A hose made
from EPDM rubber is usually resistant to ECD. Try to find hoses made from this.
It should say right on the hose what material it's made from.
Jim Moore
Sr. Product Engineer, Engine Electrical
BMW Group.
69 2000 RHD Fairlady......in billions of pieces(the middle of a frame-off) and
moving our way to NY......as some of you may have heard, BMW is consolidating
Land Rover into their offices in NJ, so I am moving up to the area...Orange
County, NY to be specific
Fred Johnson wrote:
> 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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