1. Phenomenon
When the engine is operating, the oil pressure gauge indicates an excessively high oil pressure value that exceeds the specified limit.
2. Cause Analysis
From the principle that the lubrication system generates pressure by the oil pump, it can be known that the lubricating oil in the system can generate pressure mainly due to the resistance of the oil flow in the pressure section within the system. The pressure level is related to the flow resistance of the oil in the system. When the flow resistance of the oil in the system is large, the oil pressure is high; when the flow resistance of the oil in the system is small, the oil pressure is low. Thus, if the oil pressure in the lubrication system is excessively high, it must be caused by the excessive flow resistance of the oil in the system.
In addition, if the oil pressure display device malfunctions and shows an inaccurate oil pressure value (i.e., indicating an excessively high oil pressure), it may be mistakenly believed that the oil pressure in the lubrication system is excessively high.
Common reasons for the increase in oil flow resistance include:
(1) High oil viscosity
The viscosity of the oil indicates the magnitude of the internal friction resistance when the oil flows. The viscosity of the oil is related to the engine temperature. When the engine temperature is low, the oil viscosity is high; conversely, when the engine temperature is high, the oil viscosity is low. When the oil viscosity is high, the fluidity is poor but the sealing property is good, and the leakage is small. If the oil viscosity exceeds the specified value, the flow resistance of the oil in the lubrication system will increase, and the pressure will rise. Thus, when the engine temperature is low or the oil itself has a high viscosity (due to improper selection of the oil brand, that is, the oil brand is not suitable for the ambient temperature, such as using a summer-grade oil in winter), the oil pressure will be high.
(2) Insufficient clearance at pressure-lubrication parts or blockage of the fine oil filter
From the oil circuit, it can be known that the flow resistance of the circulating oil circuit in the lubrication system is equal to the sum of the reciprocals of the flow resistances of the parallel branches. The clearance at pressure-lubrication parts such as the camshaft journal, connecting rod journal, crankshaft journal, and rocker arm journal, if the clearance is too small, the filter element of the fine oil filter is too dirty, and the oil circuit is blocked, as well as the adjustment pressure of the pressure-limiting valve being too high, will all increase the flow resistance of the oil circuit and raise the pressure.
(3) Improper adjustment of the pressure-limiting valve
From the composition and working principle of the pressure-limiting valve, it can be known that the pressure-limiting valve limits the oil pressure by relying on the balance spring and ball valve (or cone valve) and keeps the oil pressure within the specified value. When the oil pressure exceeds the specified value, it overcomes the elastic force of the spring and pushes the valve to release pressure into the system, and when the oil pressure is lower than the elastic force of the spring, the valve is closed under the action of the spring, thereby limiting the pressure within the specified range. Thus, the oil pressure in the lubrication system depends on the size of the spring elastic force. If the adjusted spring elastic force is too large, it will cause the oil pressure in the system to be excessively high.
3. Diagnosis and Elimination
(1) If the oil pressure is significantly high when a new construction machinery is put into use or after maintenance of the engine, it indicates that the clearance between the shaft necks and bearings (wedges) at the pressure-lubrication parts is too small, or the adjustment pressure of the pressure-limiting valve is too high. One should carefully check the clearance between the shaft necks and bearings at the pressure-lubrication parts. If the clearance is too small, it should be adjusted or scraped to avoid burning the mating parts due to insufficient clearance.
(2) If a diesel engine that has been in use for a long time shows an excessively high oil pressure, it indicates that the fine oil filter is clogged. It should be cleaned.
(3) If the oil pressure is excessively high when the diesel engine is at a low temperature, and the oil pressure returns to normal when the engine temperature rises, it indicates that the reason for the excessively high oil pressure is the low temperature of the diesel engine.
(4) If the oil pressure significantly increases after replacing the oil, it indicates that the oil brand selected is inappropriate. For example, using a higher viscosity oil in winter, which will often cause the oil pressure to be excessively high. It should be replaced with an oil suitable for the season.
The higher the oil brand (the larger the number), the lower the viscosity. The higher the oil viscosity, the greater the viscosity. Generally, in a normal environment, HC-14 grade oil can be used. In cold northern regions, HC-11 and HC-8 grade oils with lower freezing points can be selected. The oil pump is broken. Just replace it with a new one.
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Post time: Feb-24-2026