After a cpc3l forklift has been running for more than two years, the engine water temperature is abnormal. After the cold car starts, the water temperature rises rapidly and boils in a short time. It returns to normal only after adding cooling water. After a detailed inspection of the cooling system (during which the water pump, thermostat and fan belt have been replaced successively), no obvious fault is found. Finally, the engine was disassembled and inspected, and a 25mm long crack was found on the cylinder liner of the third cylinder. After replacing the cylinder liner, the fault was eliminated.
The cooling system of domestic forklift truck is relatively simple in structure, which is generally composed of cooling fan, radiator, thermostat and other components. The cooling fan is often driven directly by the engine, and the fan speed is consistent with the engine speed. The control of cooling water temperature mainly depends on thermostat. This is quite different from the electronic fan controlled by temperature sensor and the radiator with adjustable shutter used in ordinary cars. This structure is characterized by convenient maintenance and low cost. The disadvantage is that the control of cooling water temperature is not sensitive. The water temperature of the engine is mainly related to whether the thermostat works normally, whether the water pump can establish sufficient pressure and whether the cooling fan can reach the standard speed. To judge the failure of the cooling system, we should also judge whether these elements work normally.
1. Inspection of thermostat
At present, the thermostat used in the engine is mainly wax thermostat. Its main performance index is that the thermostat should have different lift under different water temperatures. So as to dynamically control the cooling water temperature. For checking the thermostat without disassembling the cooling system, it is mainly judged by the temperature difference between the inlet pipe and outlet pipe of the radiator. There should be a significant temperature difference between the inlet and outlet pipes when touched by hand during the period before the cold start of the engine. After working for a period of time, the temperature difference is significantly reduced. When the engine reaches the normal operating temperature (80 ℃ - 90 ℃), there is no obvious temperature difference by hand. Of course, the most accurate detection method is to remove the thermostat, place it in hot water, heat it gradually, and check the opening temperature and lift of the valve.
2. Inspection of water pump
The power source of continuous circulation of cooling water in the cooling system comes from the water pump. Whether the water pump can establish sufficient pressure is the key to the normal operation of the cooling system. When adding cooling water, if the cooling liquid level decreases significantly with the increase of engine speed, it indicates that the water pump works normally. Otherwise, the water pump and impeller may be loose and the cooling water cannot be circulated. In domestic forklift engines, the water pump, generator and cooling fan share a belt, so the tightness of the belt directly affects the speed of the water pump, fan and generator. Press down the middle of the belt with your fingers, and the lower deflection should be 11-13mm (cpc3l model). If it is too high, the water temperature will be too high, and if it is too small, the water pump bearing and generator bearing will be damaged.
3. Cooling fan
For the detection of fan air volume, a thin paper can be placed in front of the radiator. When the engine is running, if the paper can be blown away, it indicates that the air volume is sufficient. This is different from the inward suction of the car fan of the front engine. The blades shall not be installed reversely, and the fan discharge shield shall be complete and effective.
4. Radiator
The radiator of the forklift is placed at the rear of the vehicle. Due to the low chassis of the forklift and the poor working environment in the factory, some sundries and dust are easy to accumulate on the surface of the radiator. If they are not cleaned in time, the heat dissipation effect will be seriously affected. After daily operation, the radiator surface shall be carefully cleaned, and the use of high-pressure water gun shall be avoided as far as possible. Because the tube wall of the radiator is very thin, if the cleaning pressure is too high, it is easy to shrink and affect the circulation effect. In addition, it is strictly forbidden to use "hard water" in the cooling water to prevent scale in the radiator, resulting in insufficient addition of cooling water.
After checking the above main components and judging that there is no obvious fault, the problems of other systems should be considered. For example, whether there is too much carbon deposition in the combustion chamber, whether the injection time of the diesel engine is too early or too late, whether the cylinder gasket is burned out or whether the cylinder block and cylinder liner have cracks. As listed at the beginning of this article, the fault phenomenon is that the cracks in the cylinder liner make the high-pressure gas rush into the water jacket and emit fierce bubbles, just like the boiling of cooling water. In short, the faults of engine cooling system are various, but as long as we keep a clear mind and carefully analyze the essence of the problem, we can still find a solution.
