[passthebuck]

ok-back to highskool chemistry. aluminum is more reactive than iron & steel. Aluminum is the most reactive metal in the cooling system SO it gets attacked first by the acidic coolant. Coolant becomes acidic over time due to its rust inhibitors & the like breaking down. I had a similar problem - my aluminum thermostat housing was being eaten away SO I bought a MOTORAD radcap that hangs a piece of magnesium down into the coolant. Magnesium is MORE reactive than aluminum so it gets eaten first. The magnesium is called a sacrificial anode & it works. One could even do the same thing by throwing a pebble-sized hunk of magnesium down the neck of their radiator once or twice a year BUT you couldnt monitor how fast the anode is being eaten... A cheap source of magnesium are some old lawnmower decks (cast magnesium). Check out this link i found:

http://www.team.net/html_arc/datsun-.../msg00807.html

I know they're talkin about Datsuns BUT it is relevant to us too.