As the temperature decreases, the fluidity of diesel fuel decreases and waxing occurs. Diesel fuel can become viscous, and its fluidity can be compared in this state to the viscosity of honey. As a result of thickening, the fuel filter becomes clogged. For this reason, diesel fuel manufacturers add additives to diesel fuel in winter to maintain the desired fluidity and ensure engine start at temperatures from -15°C to -22°C.
However, the use of additives does not always ensure perfect engine performance. So that the fuel filter does not clog during the cold season, it is heated by the so-called «return lines» - excess fuel flowing through the return hose back into the fuel tank. Fuel, passing through the injection pump, heats up. There is a bypass valve on the return fuel line, which, depending on the ambient air temperature, regulates the flow of fuel flowing back. At temperatures below +15°C, the fuel heated in the injection pump is fed into the fuel filter. When the temperature in the filter exceeds 31°C, the bypass valve closes and excess fuel is directed directly to the fuel tank. The bypass valve is located on the top end of the fuel filter.
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