Deposits refer to the formation of solid layers coating the walls of the cooling system or blocking narrow coolant passages as in the radiator and heat core. Depoits, called scale will form on the hotter zones in the cooling sytem due to the use of hard water containing containing magnesium and calcium. Deposits can also form when traditional corrosion inhibitor such as silicates, fall out of the coolant and are carried to narrow sections of the system where plugging may occur. Finally, deposits can be formed from corrosion products and lead to plugging. Solder bloom is one such deposit.