Fuel heating device (Audi A6 C5)

As the outside temperature decreases, the fluidity of diesel fuel decreases due to paraffin crystallization. For this reason, additives are mixed into the fuel to increase fluidity to temperatures of -15°C and -22°C, respectively (Super-Diesel).

However, this is not always sufficient, so the fuel filter is heated. This is ensured by the fuel returning from the fuel pump to the tank. This fuel is heated by compression in the fuel pump. There is a valve in the fuel return line that changes the direction of the heated fuel flow depending on the filter temperature. At temperatures up to +15°C, the filter is heated by the heated fuel. If the fuel temperature rises above +31°C, the valve switches and the heated fuel returns directly to the fuel tank. The valve is mounted directly on the fuel filter.