Fuel filter — preheating system (VW Passat B3)

In order for the fuel to remain liquid even at low ambient temperatures, it is preheated. This is due to the excess fuel that is normally returned from the high-pressure fuel pump to the fuel tank. When flowing through the high-pressure fuel pump, this fuel is automatically heated. In the return fuel line there is a control valve that controls the fuel flow depending on the temperature of the fuel filter.

At temperatures below 0°C, heated fuel from the high-pressure fuel pump is directed to the filter. If the temperature of the fuel supplied to the high-pressure fuel pump in the filter rises above +10°C, the control valve switches the flow, and excess fuel from the high-pressure fuel pump is directed directly to the fuel tank via the return fuel line. The control valve is located in the upper part of the fuel filter.

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