With the goal of enhancing diesel engine adaptability to low-temperature environments and exploring cold-start potential at - 50 °C, this paper develops a one-dimensional simulation model for the cold-start system. The model is based on a method that utilizes a diesel heater to warm the coolant, which in turn heats the engine block and oil. The heating condition of coolant and oil of a 10-cylinder V-type engine within a specified time under a -50 °C environment is studied through simulation. We further optimized the cold-start process by enhancing the coolant flow distribution within each circulation circuit to improve overall thermal management and start-up efficiency. The results show that: at an ambient temperature of -50 °C, with a heating power of 80 kW, a total flow rate of 110 L/min, and an engine block flow rate of not less than 54 L/min, the diesel engine can raise the coolant temperature at the engine outlet to 40 °C and the oil temperature to -35 °C within 20 minutes. Through flow optimization, by maximizing the flow rate of the engine block heating circuit and reducing the flow diversion of the intercooler, the coolant temperature at the engine outlet can reach 40 °C in 18.9 minutes, while the oil is heated to -34.9 °C, and the final heating coolant temperature reaches 44.4 °C at 20 minutes. Compared to the situation without flow optimization, the time for the engine outlet coolant temperature to reach 40 °C was shortened by 0.55 minutes, and the final heating coolant temperature increased by 2.2 °C. Based on relevant experiments and the dynamic viscosity curve of 5 W engine oil, this paper holds that the starting conditions of a diesel engine can be met when the engine outlet coolant temperature reaches 40 °C, and the engine oil temperature reaches -35 °C.