Low oil pressure? It's all lube in the pan!

February 02, 2024

Low oil pressure? It's all lube in the pan!

I believe that all diesel engine users know that low oil pressure is a very serious abnormal fault. Not only can not work normally, but also may cause damage to the equipment. The vast majority of customers first reaction will be the oil problem. However, in the end, after various investigations, it was found that the cause of low pressure was the equipment itself. Today, what are the factors that affect the low pressure of diesel engines?

The oil is low

If the amount of oil is insufficient, the amount of oil in the oil pump will be reduced or the oil will not be filled due to the entry of air, so that the oil pressure will drop, and the crankshaft and bearing, cylinder liner and piston will be aggravated by poor lubrication. Therefore, the oil level in the oil pan should be checked before working every day to ensure the normal oil level, and the same model of oil produced by the same manufacturer should be added when insufficient.

The oil pump does not rotate

If the flat key of the drive gear and drive shaft of the oil pump is damaged or falls off; The damage of the filter will cause the oil pump to inhale foreign matter, and the gear will be stuck, which will stop the oil pump and reduce the oil pressure to zero. At this time, the damaged flat key or filter should be replaced.

Oil pump wear

When the gap between the pump shaft and the bushing, the gap between the gear end face and the pump cover, the tooth side clearance or the radial clearance is too large due to wear, it will lead to the reduction of the pump oil and the oil pressure. At this time, the worn parts should be replaced, and the inner plane of the pump cover should be ground to restore the clearance between it and the gear end face to the standard range.

Excessive engine temperature

If the engine cooling system is too much scale, poor heat dissipation, long-term overload operation or the fuel supply time of the fuel injection pump is too late, the engine will overheat, accelerate the aging, deterioration, thinning of the oil, leakage from the various coordination gaps, and the pressure is reduced. The scale should be removed, the fuel supply time should be adjusted, and the engine should work within the rated load.

Diesel engine crankshaft clearance

After the engine is used for a long time, the clearance between the main crankshaft and the connecting rod bearing gradually increases, the leakage increases, and the oil pressure decreases. The pressure decreases by 0.01MPa when the clearance increases by 0.01mm. At this time, the crankshaft can be trimmed, and a new connecting rod bearing and main bearing can be selected to restore its matching clearance.

The bypass valve is damaged

In order to maintain the normal oil pressure of the main oil passage, a bypass valve is provided. If the pressure regulating spring is softened or improperly adjusted, the mating surface of the valve seat and the steel ball is worn or stuck and closed loosely, the oil return will increase, and the pressure of the main oil passage will decrease. At this time, the bypass valve should be removed for inspection, and finally the pressure should be adjusted to the normal range.

Engine oil radiator

External leakage will pollute the engine surface, pressure drop; The internal leakage makes the oil enter the water tank, the cooling effect of the cooling system becomes poor, the engine overheats, the oil becomes thinner, and the pressure drops. Remove the radiator, repair or replace it, and restore its function.

The pressure sensor is faulty or the oil passage is blocked

If the pressure sensor fails 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 done: the engine is idling, loosen the tubing connector, observe the oil flow, determine the fault location, replace the pressure sensor or clean the oil passage.

The pressure limiting valve set pressure is too low

In the lubrication system, the oil pumped by the oil pump must be guaranteed to the appropriate pressure before reaching the lubricating parts of the engine. If the setting pressure of the pressure limiting valve is too low, the pressure regulating spring becomes soft or the sealing surface leaks, the setting pressure will be too low. At this time, the pressure limiting valve should be adjusted to restore the pressure to normal.

The oil is not the right grade

Different engines need to add different grades of oil, and the same type of engine should also use different grades of oil in different seasons. If the selected oil is not suitable or inferior oil, the engine will increase the leakage and reduce the pressure due to too low viscosity when running. Should be correct and reasonable selection of oil, adapt to different models or seasons.

Engine oil filter

When the oil filter is blocked and cannot flow, the bypass valve located on the base is opened, and the oil enters the main oil passage directly without filtering. If the opening pressure of the bypass valve is set too high, when the oil filter is blocked, it can not be opened in time, the oil pump pressure will rise, the internal leakage will increase, the oil supply to the main oil passage will decrease, and the oil pressure will decrease. The oil filter should be clean; Adjust the opening pressure of the bypass valve correctly, replace or repair the damaged components or mating surfaces in time, and restore its normal working performance.

Engine filter is blocked

Under normal circumstances, the oil pressure should be higher at the large throttle than at the small throttle, but sometimes abnormal situations will occur. If the oil is too dirty and too sticky, it is easy to block the filter collector. When the engine is running at a low speed, due to the small amount of oil absorbed by the oil pump, the main oil passage can still establish a certain pressure, so the oil pressure is normal; However, when the accelerator is operated at high speed, the oil absorption of the oil pump will be significantly reduced due to the excessive resistance of the filter collector, so the indicator value of the oil pressure gauge will decrease due to the insufficient oil supply of the main oil passage. The suction filter should be cleaned or the oil replaced.

By eliminating these faults, mechanical failure is not terrible, as long as you understand the working principle of the system, careful analysis, you will be able to eliminate the fault, but do not blindly disassemble, otherwise, it will be twice the result with half the effort, and even damage the normal working components.

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