Non EFI question, desperate for help, save my TPI manifold!

[George M. Dailey]

First off, excellent asci schematic by dn. I needed that info about 10 years
ago when I was attempting to build an EFI from scratch.

Not to cause a flame war, but I know of no other people to ask this question. 

I removed my original '68 chevy 302 (vintage) aluminium intake from my 350
engine and got a terrible surprise. Apparently, some type of
electro-chemical reaction has corroded the mating surfaces of the intake at
the water crossovers. I noticed a leak forming several months ago but did
nothing because of the planned TPI conversion. I thought it was a intake
gasket leak. The strange thing, is that the interior surfaces of the water
jackets show no evidence of this active corrosion.

Is this 'common' for aluminium intakes? It's new to me.
What caused this? And most important of all, how can I be sure the same
thing will not happen to my $$TPI$$ manifold?

The only thing different about my cooling system is that the inlet radiator
hose has a metal (steel) Tee installed with a two terminal temperature
switch in one port.  One side is attached to +12v (switched) the other goes
to the cooling fan relay. Both terminals are insulated from the coolant, I
think :{}   Could this be a possible cause?

I sure some one has seen this before. Any help would be greatly appreaciated. 

George M. Dailey
gmd at tecinfo.com