The handling methods for the simultaneous excessively high oil and water temperatures of imported excavator engines

Solutions to the problem of excavator engine temperature

In the process of mechanized road construction, when the oil temperature and water temperature of the engine are both too high, how should it be handled? Based on years of experience, the author believes that if the quantity of oil and water is sufficient or only slightly lacking, the oil temperature should be reduced first, followed by the water temperature. The reasons are as follows.

Excessively high oil temperature is highly harmful to the engine

The so-called excessively high engine temperature refers to the oil temperature and water temperature of the engine exceeding 90℃. When both of these temperatures are too high at the same time, it will affect the normal operation of the engine and cause certain harm to it. The temperature of water mainly indicates the combustion of the engine and the thermal condition of high-temperature parts such as the piston and cylinder wall. Therefore, excessively high water temperature will deteriorate the combustion conditions, cause thermal expansion of high-temperature parts, reduce the gap between the piston and the cylinder wall, and result in severe wear or "cylinder pulling". The oil temperature mainly indicates that the crankshaft and bearings generate heat due to friction, and the engine oil dissipates most of this heat. The balance between the generated heat and the dissipated heat (manifested as stable oil temperature) is relative. When the heat generation exceeds the heat dissipation, the temperature of the bearing bush will rise, and the local temperature will reach the melting point of lead, causing the lead in the bearing bush to melt and precipitate. When a large amount of lead precipitates, the bearing surface of the bearing bush becomes smaller and more uneven, accelerating wear. In severe cases, the local temperature can exceed the melting point of copper (1083℃), and copper begins to melt, eventually leading to severe erosion of the crankshaft and bearing or the consequence of "bearing seizure of the shaft". According to the test, when the oil temperature reaches 110℃, the oil film temperature in the bearing clearance can reach 150℃. When the oil film temperature reaches above 150℃, it is prone to cracking and forming semi-dry friction. As the crankshaft bearing is a copper-lead alloy, if the reduction measures are inappropriate, the bearing temperature will be too high, causing the lead to melt and precipitate. The consequences would be unimaginable. Therefore, when both the oil and water temperatures are too high at the same time, the oil temperature should be reduced first.

Lowering the oil temperature can slow down the rate at which the water temperature rises

To lower the oil temperature, the method of "reducing load and lowering speed" is usually adopted. At this point, although the coolant takes a long time to exchange heat at the high-temperature parts, the water flow rate slows down, prolonging the heat dissipation time. At the same time, due to the reduction in load and the decrease in rotational speed, the heat generated by the friction of each moving part also decreases accordingly. Therefore, lowering the oil temperature not only reduces the heat generated by the engine but also indirectly decreases the heat absorbed by the coolant, thereby also slowing down the rate at which the water temperature rises.

Oil temperature is one of the main factors affecting oil pressure

When the engine oil temperature is too high, it not only increases fuel consumption (leakage, evaporation, combustion), but also affects the quality of the oil, making it difficult for the oil film on the friction surfaces of various engine parts to form and maintain, resulting in the inability to establish the oil pressure in the main oil passage, thereby accelerating the wear of the parts. The influence of water temperature on oil pressure can only be achieved through oil temperature. Therefore, it has a certain degree of indirectness and requires a certain amount of time.

Reducing the water temperature first has a significant impact on the establishment of oil pressure in the engine's main shaft oil passage

It is well known that to lower the water temperature, the method of "reducing load and increasing speed" is generally adopted. When the rotational speed is too high, it will increase the inertial force and centrifugal force of the piston coupling group, thereby increasing the load on the crankshaft bearing. At the same time, the relative friction speed between the journal and the bearing bush will also increase, causing the heat generated per unit time to rise, the oil volume of the oil pump to decrease, and a large amount of engine oil to be flung out from the main oil passage. As a result, the friction surfaces of each component will wear out more rapidly due to the lack of sufficient lubricating oil, and the oil temperature will rise further.