Engine high temperature is a common fault of construction machinery. In hot summer, the heat dissipation capacity of various water-cooled engines is reduced, which is prone to high temperature and even “boiling”. The construction conditions of construction machinery are poor, which is more prone to high temperature failure. Taking the small excavator powered by water-cooled diesel engine as an example, this paper analyzes the causes and Countermeasures of high engine water temperature in detail, so as to provide reference for the normal use of small excavator and reduce the high temperature of engine in summer.
Under normal conditions, the optimal water temperature for engine operation is 78 ~ 93 ℃. When the water temperature is greater than 95 ℃, it belongs to engine high temperature. Engine high temperature has the following manifestations.
(1) Small excavator operates under light load and the water temperature is normal; Once heavy load operation, the water temperature will rise suddenly, and when no-load, the water temperature will drop rapidly.
(2) During the operation of small excavator, high temperature suddenly occurs.
(3) During the normal operation of small excavators, the water temperature remains high, and even rises to about 95 ℃. A little carelessness will “boil the pot”.
Causes and Countermeasures of engine high temperature of small excavator
(1) If the water temperature of the engine is too high, the moving parts will expand by heating and damage the normal fit clearance and stick.
(2) The engine oil fails at high temperature, resulting in the lack of lubrication and jamming of the parts.
(3) The mechanical strength of the parts is reduced or even damaged due to high temperature.
(4) The decrease of combustion chamber charging efficiency leads to insufficient engine power.
(1) Insufficient coolant. When the engine is at high temperature, first check the amount of coolant. If it is insufficient, replenish the coolant.
(2) Water pump failure. Open the water tank cover, start the engine, make the engine run alternately at high speed and low speed, and check whether the water in the water tank has obvious rolling phenomenon. If there is no rolling, it can be considered that the water pump is faulty.
(3) Thermostat failure. When the engine temperature is too high, you can touch the temperature of the upper and lower water pipes to judge the fault. If the temperature difference between the two water pipes is very large, it can be judged that the thermostat does not work. Remove the thermostat and check the opening temperature of the thermostat. Hang the thermostat and thermometer in the water container, then heat the container, check the starting opening temperature of the thermostat, continue heating, record the full opening temperature of the thermostat, and check whether the two temperatures are within a reasonable range. Then stop heating. When the water temperature drops below 82 ℃, the thermostat should be in the closed position. Otherwise, the thermostat needs to be repaired or replaced. If accessories cannot be purchased temporarily, the thermostat can be removed for emergency use.
(4) Fan failure. Check whether the fan blade is installed reversely, whether the specification is correct (outer diameter), whether the fan blade is damaged or seriously deformed, etc. If so, exclude it. There is also an electromagnetic fan. Check whether the circuit is damaged. If yes, replace it.
(5) Fan belt failure. Check whether the fan belt is missing and whether the tightness is normal. Press the fan belt by hand to check whether the tightness is normal (adjust the tightness of the belt. It is correct to press the belt with your fingers, and the sag shall not be greater than 10mm. If it is too tight, the water pump will be damaged). If the belt is loose, further check the fan belt for slipping, etc.
(6) Water cooler (water tank) failure.
① The radiator of the water tank is blocked by oil sludge, dust, grass leaves, insects, etc., resulting in reduced heat exchange capacity of the inlet air, resulting in high water temperature. In such cases, blow with compressed air, flush with low-pressure water flow or remove for cleaning from the back of the water tank after the engine is shut down to remove sundries.
② The radiator of the water tank is deformed and stuck. Due to mechanical damage and other reasons, the heat sink is stacked or bonded together, so that the air flow cannot pass through the radiator core smoothly, resulting in poor heat dissipation. The solution is to carefully move the heat sink to the original position with thin steel sheet (such as waste hacksaw blade), restore the flat shape of the heat sink or replace the radiator.
③ The radiator core pipe of the water tank is blocked. The operator fills the cooling system with river water with high impurity content for a long time, so that the sediment and dirt in the cooling water adhere to the inner wall of the core pipe, resulting in the core pipe being blocked or blocked. The inspection method is: after the engine is hot, touch the upper and lower parts of the core tube by hand and pay attention to the temperature difference. Under normal conditions, there is a temperature difference between the upper and lower parts, but there is little difference. If the temperature difference between the top and bottom of the core pipe is obvious (because there is no hot water passing through the lower part), it indicates that the core pipe is blocked; If more than 15% of the total number of core tubes are blocked, the cooling effect will be greatly reduced. At this time, remove the radiator, wash it in hot water containing 5% ~ 10% soda (80 ~ 90 ℃), dredge the core pipe with a steel drill, and then wash it with hot water.
Causes and Countermeasures of engine high temperature of small excavator
(7) Oil cooler or intercooler is blocked. The heat sink of oil cooler or intercooler is filled with oil sludge, dust, grass leaves, insects, etc., which reduces the heat exchange capacity of inlet air, resulting in high water temperature. In such cases, blow with compressed air or flush with low-pressure water flow from behind the radiator after the engine is shut down to remove sundries.
(8) Air guide and cooling system failure. Water Cooled Engines mostly adopt suction cooling. The air on both sides of the water tank shall not have convection. Except that the cooling air duct of the water tank is connected, other parts shall be isolated. It can not be ignored that after many machines have been used for a period of time, the barrier materials are aging and fall off seriously, which makes there is an airway around the water tank, reducing the air flow through the water tank and causing high temperature. In addition, the hot air of the engine flows back, that is, the air inhaled by the fan is hot air, which will also cause high temperature. In actual maintenance, there are many such cases, so a new sponge should be installed again; In order to increase the ventilation, the side door on the water radiator side can be perforated (ventilation side door).
(9) The volume of the engine is too dirty. There is too much scale in the water cooling system, the heat transfer is blocked, and the heat cannot be dissipated in time, which will also lead to high temperature. The key to prevent and reduce scale formation is to reduce minerals and metal ions in scale and soften water quality. The main measures are as follows: ① magnetization of water quality; ② Using the softening characteristics of boiling water; ③ Adding softener method; ④ Preservative (potassium bicarbonate K2Cr2O7) method; ⑤ Good coolant is clean river water, rain water and snow water; ⑥ Add cooling water in time to prevent the liquid level of water radiator from being too low; ⑦ Use antifreeze all year round.
(10) The circulating water pipe is blocked. Due to long-term corrosion, the rubber in the upper and lower water pipes will fall off, preventing the circulating water flow and causing high temperature.
(11) Cooling system air resistance. If there is air in the cooling system, air resistance will be formed, resulting in poor cooling water circulation and excessive engine temperature. The following methods can be adopted to solve the problem: let the engine run at high speed, gently unscrew the water tank cover until the gas is just released, and then some cooling water will flow out with the gas. Repeat this for many times until you feel that the gas is discharged (at this time, the temperature of the upper and lower water pipes will be significantly different by touching with your hand). After troubleshooting, the cooling water shall be supplemented in time.
(12) Pseudo high temperature phenomenon. The display screen of small excavator shows that the water temperature is high, but it is actually not high. When the small excavator operates in gears 7 and 8 in normal S mode, use the infrared thermometer to measure the water temperature at the sensor and compare it with the temperature on the display screen to judge whether the water temperature is false high temperature? If it is a false high temperature, please check the display sensor and related circuits.
resulting in high water temperature. This situation is due to the abnormal operation of relevant parts of the engine or the high temperature caused by the change of working environment, such as the high temperature caused by factors such as reduced engine power, increased load and reduced boiling point in plateau areas, which is similar to the “inflammation” of relevant parts of the human body. There are several common reasons.
(1) The fuel supply advance angle of diesel engine is premature or delayed. No matter whether the fuel supply advance angle is ahead or behind, the contact area between high-temperature gas and cylinder wall increases and the time is prolonged during combustion, and the heat transmitted to cooling water increases, resulting in a sharp increase in cooling water temperature, which is often accompanied by difficulties in starting, black smoke from exhaust, engine weakness and other phenomena. The fuel injection timing shall be corrected again to reach the specified value.
(2) Excessive wear of moving parts. After excessive wear of cylinder liner, bearing bush and other components, additional heat will be generated during machine operation. If these heat exceed a certain value, the water temperature will also be too high. Excessive wear of cylinder liner is often accompanied by the following phenomena. ① Engine power decreases. ② Oil burning phenomenon. ③ Excessive exhaust emissions. When the bearing bush is excessively worn, it is usually accompanied by the following phenomena: the oil temperature rises faster; The oil pressure decreases obviously after the oil temperature increases; There was a dull knocking sound.
(3) Overload operation. Confirm whether the machine is overloaded for a long time. If so, immediately change to normal operation, and check whether the water temperature is normal after a period of time.
(4) Insufficient air intake, insufficient combustion, serious black smoke from the engine, resulting in high temperature: ① check whether the air filter element is blocked; ② Check whether the air filter inlet is blocked; ③ Whether the turbocharger is damaged; ④ Check whether the connection between turbocharger and engine air inlet is damaged. If so, take corresponding measures to solve it.
(5) Cylinder gasket damage causes high temperature. If the cylinder pad is burned by high-temperature gas, high-pressure gas will rush into the cooling system to make the cooling water boil. To judge whether the cylinder gasket is burned, turn off the engine, wait a moment, restart the engine and increase the speed. If you open the radiator water filler cap at this time, you can see a large number of bubbles, and small water droplets are often discharged with the exhaust gas in the exhaust pipe.
Therefore, it can be concluded that the cylinder gasket has been damaged and should be replaced with a new one. If the above methods are checked and the water temperature is still high, the heat balance may be insufficient in the design of the cooling system, and the following methods can be adopted for improvement.
(1) Reduce the diameter of the engine fan pulley, increase the fan speed and increase the ventilation.
(2) An electric fan is installed in front of the water tank to increase the ventilation.
(3) Increase water tank capacity, etc.
The above lists some causes and treatment methods of engine overheating. When the engine is high temperature, we must carefully observe, analyze and judge to find out the causes of high temperature, so as to quickly diagnose and eliminate the faults.
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