NOVELTY - The system (10) has a charging circuit (30) filled with fluid and closed via a heat accumulator (20) i.e. latent heat accumulator, and a heat exchanger (40). The heat exchanger is thermally arranged at a catalytic converter (50) in an exhaust gas device (12) of an internal combustion engine (11). A discharge circuit (60) is filled with another fluid and closed via the heat accumulator and the internal combustion engine. The charging circuit and the discharge circuit are decoupled from each other. A mixing device (70) i.e. diffuser, is arranged in the discharge circuit or heat accumulator.    USE - Heat accumulator system for an internal combustion engine e.g. petrol engine and diesel engine, of a motor car. Can also be used for a hybrid electric vehicle.    ADVANTAGE - The discharge circuit is filled with fluid and closed via the heat accumulator and the internal combustion engine, and the charging circuit and the discharge circuit are decoupled from each other, so that the accumulator system efficiently supplies waste heat in a waste gas system to the heat accumulator during operation of the internal combustion engine of the motor car in a charging process such that the heat accumulator efficiently accumulates the heat for other applications, and supplies the accumulated heat to the internal combustion engine via the discharge circuit during a discharging process of the heat accumulator to preheat the internal combustion engine. The system thus enables working of the internal combustion engine in an efficient manner.    DETAILED DESCRIPTION - The discharge circuit is selected from an engine cooling water circuit and/or an oil circuit. An INDEPENDENT CLAIM is also included for a method for operating a heat accumulator system for a motor car.    DESCRIPTION OF DRAWING(S) - The drawing shows a simplified schematic side view of a motor car with a heat accumulator system.    Heat accumulator system (10)    Internal combustion engine (11)    Exhaust gas device (12)    Heat accumulator (20)    Charging circuit (30)    Heat exchanger (40)    Catalytic converter (50)    Discharge circuit (60)    Mixing device (70)