Phosphate-containing, glycol-based coolant mixtures which are stable in hard water and are free of nitrites, silicates, amines and borates containa) 0.5-3% by weight of ammonium and/or alkali metal phosphateb) 2-5.5% by weight of ammonium or alkali metal benzoatec) 0.2-1.5% by weight of ammonium or alkali metal molybdated) 0.2-0.8% by weight of ammonium or alkali metal nitratee) 0.05-0.4% by weight of benzotriazolef) 0.05-0.4% by weight of tolyltriazoleg) 0.005-0.35% by weight of a water-soluble magnesium compoundh) 0.02-0.5% by weight of an oligomeric or polymeric carboxylic acid with a molecular weight of 1,000-100,000,i) 0.05-5% by weight of water and the amount of glycol necessary to make up to 100% by weight.