The effect of tolyltriazole (TTA) in H2SO4 (pH = 0.4) and Na2SO4 (pH = 6 and 11) on the corrosion of brass, carbon steel and aluminium used in automotive cooling systems was investigated by electrochemical methods, depending upon the pH, concentration and temperature. The corrosion potentials, corrosion rates, inhibition efficiencies and activation energies have been determined. The results have shown that TTA has the highest inhibition efficiency on brass at pH = 0.4, but the efficiency decreases with increasing pH, While TTA is used as an effective inhibitor for carbon steel at pH = 0.4, 6 and 11, efficiency reduces with decreasing inhibitor concentration. TTA accelerates the corrosion of aluminium at pH 0.4 = 0.4 and 11, whereas it inhibits the corrosion at pH = 6.