Abstract: A motorization unit comprising two internal combustion engines able to run alternately or simultaneously.The two engines (20, 40) each comprise their own cooling circuit (21, respectively 41). These two circuits are each provided with an expansion vessel (26, 46) and are connected to a heat exchanger (30). The purpose of this heat exchanger is to keep the cooling circuit of one of the engines not running, at the right temperature by means of the cooling circuit of the other engine which is running, when the unit is operating in alternate mode.This motorization unit can be adapted to road, rail and aquatic vehicles.