Two serious problems confront the automotive industry in connection with the present fuel shortage, the securing of a much higher degree of fuel economy with existing equipment and the matter of future designs. These problems are of nearly equal importance.Because its fuel bill constitutes the second greatest item of expense for the Fifth Avenue Coach Co., operating in New York City, it is constantly experimenting with devices of various kinds to improve fuel economy. Of the different devices that it has tested, the thermostatic temperature-control for the carbureter appears to afford greatest possibilities of saving, and the author presents the results of tests of this device in actual service on motor vehicles.The thermostat is shown and described and comparative tests made with and without this thermostatic-control device, using the same engine, carbureter and similar equipment, under the same atmospheric conditions, are discussed and analyzed with the aid of tabulated data and charts. The matters of temperature variation and the volatility of fuel are treated in a similar manner, consideration then being given to what the desired manifold temperature is. Volumetric efficiency is discussed in some detail.The paper was presented with the primary idea of bringing out constructive criticism. The company believes that the principle of thermostatic control is correct, but that its detailed application is still a matter for further experiment. That there are certain periods during the year when the average internal-combustion engine functions with the minimum amount of trouble is scarcely open to argument. This is because at that time the atmospheric temperature is right. The company's idea is to select this period and standardize it for use throughout the remainder of the year.