Fuel heating system (VW Passat B5)

To increase the fluidity of diesel fuel at low outside temperatures, it must be heated. Heating is performed by additional pumping of fuel, which returns from the high-pressure fuel pump to the fuel tank. Passing through the high-pressure fuel pump, the fuel is heated. A regulating valve is installed in the fuel return line, which controls the fuel flow depending on the temperature of the fuel filter. At an outside air temperature below +15°C, the fuel heated by the high-pressure fuel pump is directed to the fuel filter. At an air temperature above +31°C, the regulating valve directs the fuel heated by the high-pressure fuel pump directly to the fuel tank. The regulating valve is located on the upper side of the fuel filter.

If the engine does not start at low air temperatures due to thickening of diesel fuel, do the following:

• remove the fuel filter and warm it up with steam;
• replace the fuel filter with a new one;
• warm up the injection device by pouring hot water over it.