A method and apparatus for preventing an overheating of an exhaust gas purification block for internal combustion engines in case of a high proportion of combustible gas components in the exhaust gases, in which the exhaust gases are adapted to be conducted past the exhaust gas purification block by way of a controllable by-pass line; at least during the periods when the by-pass line is opened, air preferably in the form of an air jet directed opposite to the normal exhaust gas flow is blown into the line leading into the exhaust gas purification block whereby preferably the air jet passes over the inlet opening of the exhaust gas purification block in a transverse direction.