A water-cooled combustion engine has a pump-operated cooling water circuit passing through the cooler when the engine is hot. The cooler is rendered inoperative by a thermostat-controlled by-pass line when the engine is cold. The heating means for the intake system for the engine has a cooling water chamber whose supply line is fed with heated cooling water. The circuit of the heating means is arranged parallel with the cooling circuit through the by-pass line. This heating means is automatically switched off without additional aids as the engine temperature rises, when the by-pass line is shut off by the thermostat valve.