A fuel injection system (1) with at least one fuel injector (1a) and a heatable adapter (1b), which is connected to a fuel rail (1c) and to the fuel injector (1a) of the fuel injection system (1); a thermoswitch (2) is provided in the fuel rail (1c), which is connected with an external door contact switch (3) and with the heatable adapter (1b). The thermoswitch (2) includes a thermosensor, so that a reliable cold start is ensured by the fact that, when a previously specified fuel temperature is fallen below, the thermoswitch (2) switches over and causes fuel (8) to be heated.