Abstract: A method is disclosed of protecting heated aluminum based metals subject to heat transfer through the metal to a circulating aqueous cooling solution in contact therewith. The initially constituted cooling solution contains an alkali metal silicate in an adjusted amount above 0.2 gram per liter. The solution while functioning in the cooling system is then exposed to an alkali metal silicate glass causing the glass to progressively dissolve and stabilize the silicate at a level of at least 0.1 gram per liter. The initially prepared solution may also contain ethylene or propylene glycol, alkali metal phosphates and tetraborates in a ratio greater than 4:1, and nitrate, mercaptobenzothiazole or tolyltriazole.