The behaviour of three types of steel with a variable carbon content (from 0.2 to 0.4%) is studied in medium of methanol -10% ethyleneglycol - 5% propionic acid with water concentration between the values 1% to 5%. The weight losses are measured; also the polarisation anodic and catodic curves are plotted and the corrosion parameters are established. The methods used for the analysis of the corrosion compounds are IR spectra, X-ray diffraction and chemical analysis. Finally, a corrosion mechanism is proposed and the optimum ratio between water and acid is established in order to obtain the passive oxyhydroxylic layer.