Abstract: A heat exchanger has warm coolant or liquid, for example from the engine, flow through it to heat it up. Disposed on the fuel filter is an electrical heating element that can directly heat the filter space or fuel contained in the filter housing. The heating element can be activated and deactivated in a controlled manner, for example manually, only when needed. The heat exchanger is formed of a rubber hose with a helically wound tube coil surrounding it with a sleeve being provided which surrounds the tube coil. The sleeve is made of rubber and securely connected to the hose by vulcanization.