A fuel cell system including: a fuel cell stack including plural fuel cells sandwiched between two end plates; a fuel supply system supplying a stream of fuel gas to the fuel cell stack; an oxidizer supply system supplying a stream of oxidizer gas to the fuel cell stack; a closed loop coolant circulation system driving a cooling liquid through the fuel cell stack so that the cooling liquid enters the fuel cell stack, absorbs heat from the fuel cells, and exits the fuel cell stack. The coolant circulation system includes a circulation pump driving the cooling liquid, a heat exchanger removing heat from the cooling liquid and for at least partially transferring the heat to the stream of fuel gas and/or the stream of oxidizer gas. The heat exchanger includes a tube made from a heat-conducting material and inserted into a bore in one of the end plates, the tube and the bore defining at least a first fluid channel inside the tube and a second fluid channel in a space existing between the tube and the sides of the bore in the end plate, one of the first and second fluid channels being for the cooling liquid, and the other fluid channel being for the fuel or the oxidizer gas.