Abstract: This invention relates to motor vehicles having passenger compartment heating devices. The temperature of the cooling water of an engine may be increased at idling speeds and low speed states by throttling the engine exhaust to increase fuel consumption. A throttle device is controlled in accordance with cooling water temperature and passenger compartment temperature, in response to activation by manual control. Manual control is overridden by an accelerator pedal actuated control when the load of the engine rises. Heat is extracted from the engine cooling water by means of a heat exchanger, through which air is driven into the passenger compartment. A brake is connected to an independently actuated device to throttle the exhaust to brake the engine. This arrangement is particularly suitable for use with diesel engines.