What is the phenomenon that the diesel overflow valve is broken?

Damage to the overflow valve of diesel engine will lead to high fuel consumption and difficult starting. 1. If the overflow valve is stuck in the open position, it will be difficult to start, because the fuel low pressure cannot be established smoothly and flows directly from the overflow valve to the fuel tank, so it is difficult to start. If it is stuck in the closed position, the fuel cannot flow back to the fuel tank, and the fuel injection quantity of the fuel nozzle increases, so the fuel consumption increases. 2. If it is difficult to start after replacing the fuel filter, it is necessary to remove the overflow valve for inspection. If it is stuck, replace the overflow valve. If there is anything dirty, clean it up first. After replacing the overflow valve, the oil pump should be drained, otherwise the vehicle cannot be started. 3. Diesel vehicles are easy to freeze, so the fuel with the specified label must be used. For example, if the weather gets cold, if the oil added before is 0# and the temperature is lower than 0℃, the oil pump and oil tank will freeze. As long as it freezes, it will also affect the oil return of the overflow valve. Even if-10# fuel is added, the overflow valve should be disassembled for cleaning.