A method for determining the cloud and solid points of summer and winter diesel fuels on a Fazafot photocolorimeter is described. The instrument was calibrated with solutions of individual waxes in naphtha to determine the absorption coefficient and calculate the wax content in diesel fuels based on their optical density. The temperature range of clouding of the solution is directly proportional to the distillation range of the waxes in the fuel and the hysteresis between the cooling and heating curves is inversely proportional to the width of the wax cut.