Analysis of the Causes of low engine Oil pressure

When a excavator was in operation, an alarm for an oil problem suddenly appeared on the dashboard. The driver immediately stopped the machine for inspection and checked whether the oil level and viscosity were normal through the oil dipstick. Disassemble the oil filter element and check if it is functioning properly? The inspection results show that both of the above items are normal. However, due to the lack of appropriate detection tools, further inspection cannot be carried out. The customer hopes that we can assist them in conducting further checks to eliminate faults and restore the machinery to normal operation. What causes abnormal oil pressure during the operation of an engine? First, we will conduct a detailed analysis of the causes.

The lubrication system of a diesel engine mainly consists of the oil pan, oil pump, oil filter, heat exchanger, main oil passage, distribution oil passage, low oil pressure alarm sensor, high oil temperature alarm sensor, pressure limiting valve and bypass valve. The main reasons for low oil pressure are as follows:

The engine oil level is insufficient

If the oil level is insufficient, it will reduce the oil pumping capacity of the oil pump or prevent it from pumping oil due to the entry of air, causing the oil pressure to drop. As a result, the crankshaft and bearings, cylinder liners and pistons will all wear out more rapidly due to poor lubrication. Therefore, before starting work every day, the oil level in the oil pan should be checked to ensure it is normal. If it is insufficient, the same type of engine oil produced by the same manufacturer should be added.

Two oil pumps are not rotating

If the flat key between the drive gear of the oil pump and the drive shaft is damaged or falls off; If the filter collector is damaged, foreign objects will be sucked into the oil pump, or the gears will be stuck, all of which will cause the oil pump to stop rotating and the oil pressure to drop to zero. At this point, the damaged flat key or strainer should be replaced.

3. Wear of the oil pump

When the clearance between the pump shaft and the bushing of the oil pump, the clearance between the gear end face and the pump cover, the side clearance of the teeth or the radial clearance becomes too large due to wear, it will all lead to a decrease in the oil pumping volume and a drop in the oil pressure. At this point, the worn parts should be replaced, and the inner surface of the pump cover should be ground to restore the gap between it and the end face of the gear to the standard range.

The engine temperature is too high

If there is too much scale in the engine cooling system, poor heat dissipation, long-term overloading operation or the fuel supply time of the fuel injection pump is too late, etc., it will cause the engine to overheat, accelerate the aging, deterioration and thinning of the engine oil, leak from the fit clearances, and reduce the pressure. Scale should be removed, the fuel supply time adjusted, and the engine should operate within its rated load.

The fit clearance between the main bearing and the connecting rod bearing has increased

After long-term use of the engine, the fit clearance between the main crankshaft and the connecting rod bearing gradually increases, leakage increases, and the oil pressure drops. For every 0.01mm increase in this fit clearance, the pressure drops by 0.01MPa. At this point, the crankshaft can be ground, and new connecting rod bearings and main bearings can be selected to restore their fit clearances.

The bypass valve is damaged

To maintain the normal oil pressure in the main oil passage, a bypass valve is installed. If the pressure regulating spring softenes or is improperly adjusted, or if the mating surface between the valve seat and the steel ball wears out or gets stuck and fails to close tightly, the return oil volume will increase and the pressure in the main oil passage will drop. At this point, the bypass valve should be removed for inspection, and finally the pressure should be adjusted to the normal range.

The oil radiator is leaking

Leakage can contaminate the engine surface and cause a drop in pressure. Internal leakage causes engine oil to enter the radiator, reducing the heat dissipation effect of the cooling system. The engine overheats, the engine oil thins, and the pressure drops. Remove the radiator, repair or replace it to restore its function.

8. The pressure sensor malfunctions or the oil passage is blocked

If the pressure sensor malfunctions or the oil passage from the main oil passage to the pressure sensor is blocked and the oil flow is not smooth, the oil pressure will drop. The following checks can be carried out: Let the engine idle, loosen the oil pipe joint, observe the oil flow situation, determine the faulty part, replace the pressure sensor or clean the oil passage.

The set pressure of the pressure-limiting valve is too low

In the lubrication system, the engine oil pumped by the oil pump must maintain an appropriate pressure before reaching all the lubricated parts of the engine. If the set pressure of the pressure-limiting valve is too low, the pressure-regulating spring becomes soft or the sealing surface leaks, it will all cause the set pressure to be too low. At this point, the pressure-limiting valve should be adjusted to restore the pressure to normal.

The grade of engine oil is not suitable

Different engines require the addition of different grades of engine oil, and the same model of engine should also use different grades of engine oil in different seasons. If the selected engine oil is not suitable or of poor quality, when the engine is running, the viscosity will be too low, resulting in increased leakage and low pressure drop. Engine oil should be selected correctly and reasonably to adapt to different models or seasons.

11. The oil filter is clogged

When the oil filter is clogged and cannot flow, the bypass valve set on its base is opened, and the oil enters the main oil passage directly without being filtered. If the opening pressure of the bypass valve is set too high, when the oil filter is clogged, it cannot be opened in time. As a result, the oil pump pressure will rise, internal leakage will increase, the oil supply to the main oil passage will decrease, and the oil pressure will drop. The oil filter should be kept clean. Adjust the opening pressure of the bypass valve correctly, replace or repair damaged components or mating surfaces in a timely manner, and restore its normal working performance.

The 12-filter collector is clogged

Under normal circumstances, the oil pressure should be higher when the throttle is high than when it is low, but sometimes abnormal situations may occur. If the oil is too dirty or too sticky, it is prone to clogging the strainer. When the engine is running at a low speed with a small throttle, due to the small oil suction volume of the oil pump, a certain pressure can still be established in the main oil passage, so the oil pressure is normal. However, when the throttle is increased and the engine is running at high speed, the oil suction volume of the oil pump will significantly decrease due to excessive resistance of the oil strainer. As a result, the reading of the oil pressure gauge will drop due to insufficient oil supply in the main oil passage. The suction filter should be cleaned or the engine oil replaced.

Based on the above analysis, we brought an oil pressure gauge and an oil quality analyzer to the construction site. We used the oil quality analyzer to test the quality of the oil and found that both the viscosity and the degree of contamination of the oil met the requirements. Connect the oil pressure gauge and measure the oil pressure at low speed and high speed respectively. It was found that the oil pressure was lower than 0.15MPa. Under normal circumstances, the oil pressure is 0.15MPa at low speed and 0.6MPa at high speed. From this, it can be known that the oil pressure is too low to reach the normal pressure. We inspected the bypass valve on the oil filter seat in accordance with the principle of starting from the simple to the complex and from the outside to the inside. After disassembling it, we found that the sealing between the steel ball and the valve seat mating surface was not tight, resulting in oil leakage and pressure drop. By grinding the sealing surface to restore its sealing performance, adjusting the pressure to the standard value, and the oil pressure alarm light going out, it indicates that the machinery has returned to normal and the fault has been resolved.

By eliminating this fault, it shows that mechanical malfunctions are not terrifying. As long as you understand the working principle of the system and analyze it carefully, you can definitely eliminate the fault. However, do not disassemble it blindly; otherwise, it will be twice the result with half the effort and even damage the normally working components.