re: carbon black in O-rings...I suppose the the rubber gasket in the
water pump has the same problem.

About your statement "I think, the stainless is a much lesser problem
than any other metal around." I think misses the point. Its a more
noble metal than aluminium, and will cause dissimilar metal corrosion
in unprotected systems. The other metals present are plain steel and
brass. They are more noble than Al too, brass being more than steel.

but you can't overlook the surface areas involved, here is a"back of
the envelope" estimate:

lets just say, for the sake of argument, that pipes are 7 ft long,
(therefore 14 ft total).

ID of pipe is 1.75 inches right? or is that OD?

lets be conservative and say its OD with 0.065 " wall thickness, so
ID is 1.75 - 2(0.065) = 1.62"

the internal surface area is equivalent to external surface area of a
cylinder (excluding end caps) 7' long, 1.62" diameter, which works
out to be... 2 pi r * h

so for one pipe:

A = 2 * pi * 0.81 * 84
A= 427.51 square inches

so the combined surface area of the 2 pipes would be 855 square
inches, about 5.9 sq ft, right?

That's not a trivial amount.

alistair

the area is important as this determines the amount of current. the 2
different metals determines the voltage.
On 2-Nov-10, at 9:44 AM, Zolly wrote:

Well, earlier experiences show that the Carbon in the rubber is the
main cause of the corrosion activity at the head gaskets, where the
aluminium oxide builds up and pushes the parts apart well enough to
let coolant out. Being the largest rubber in the system, is why we
see that happen more obviously than other areas such as the water
pump O ring.
I think, the stainless is a much lesser problem than any other metal
around.
Zoltan