Abstract: A radiator designed more especially for use with IC engines comprises a bank of coolant tubes extending between two coolant heaters. The bank of tubes contains not only smaller tubes with the same bore cross section but furthermore tubes with a larger bore cross section designed to reduce the resistance to flow between the two headers. The presence of such larger tubes in the radiator taking the place of tubes with a smaller cross section and having an equal cross section like the other tubes present in the bank of tubes, makes it possible to avoid using a coolant pump with a larger pumping rate and to avoid the design of the radiator to withstand a higher pressure. It is possible to accept a slight decrease in the radiator performance, such decrease being balanced by other means and in any case being offset by the cost advantages.