Under "running losses", one understands the separation or evaporation of fuel, oil, washer water, underfloor protection or engine fumes.
A small and a large fuel circuit serve the purpose of preventing fuel overheating. The large fuel circuit is required during the starting phase in order to flush the fuel injection rail with the complete delivered quantity of fuel. Power is applied to the 3/2-way valve (fuel circuit changeover valve) for this purpose. The 3/2-way valve is then deactivated, i.e. power is no longer applied, and the small fuel circuit assumes fuel supply As a result, the surplus fuel delivered by the fuel pump now only flows through the small fuel circuit and is returned to the fuel tank via the return line. Only the amount of fuel that is used by the engine is now delivered up to the injection rail. In this way, the quantity of fuel in the small circuit which is located outside the engine compartment is heated up to a far lesser extent so that fuel evaporation is also reduced.