The causes and solutions for abnormal engine oil pressure in diesel engines

Abstract

The causes and countermeasures of abnormal oil pressure were analyzed from three aspects: excessively high oil pressure, excessively low oil pressure, and no oil pressure at all.

Key words

Oil pressure flow resistance lubrication part pressure limiting valve

During the operation of construction machinery, diesel engines often experience abnormal oil pressure due to wear of components, clogging of filter elements and coolers, oil leakage or other reasons. The main manifestations are excessively high oil pressure, excessively low oil pressure and no oil pressure at all.

1. The oil pressure is too high

Excessively high oil pressure refers to the situation where the oil pressure gauge shows a value exceeding the specified limit.

1.1 The oil pressure display device is malfunctioning

The oil pressure sensor or oil pressure gauge malfunctions, the pressure value is inaccurate, the displayed value is too high, and it is mistakenly believed that the oil pressure is too high. Use the interchangeability method (that is, replace the old oil pressure sensor and pressure gauge with a good one) to check the oil pressure sensor and oil pressure gauge. If the display is normal, it indicates that the pressure display device is faulty and should be replaced.

1.2 Excessive viscosity of the engine oil

When the viscosity of the engine oil is too high, its fluidity deteriorates, the flow resistance increases, and at the same time, the oil pressure rises. If summer engine oil is used in winter, the oil pressure will increase due to excessive viscosity. In winter, due to the extremely low temperature, the viscosity of the engine oil increases, and the pressure will be too high for a short period of time when starting the engine. However, after running smoothly, as the temperature rose, it gradually dropped back to the specified value. When maintaining and servicing, the specified brand of engine oil should be selected in accordance with the requirements of the technical data. Preheating measures should be taken when starting the engine in winter.

1.3 The clearance at the pressure lubrication part is too small or the oil fine filter is clogged

If the fit clearance of pressure lubrication parts such as CAM bearings, connecting rod bearings, main crankshafts, rocker arm bearings, etc. is too small, or the filter element of the fine filter is clogged, it will increase the flow resistance of the oil circuit in the lubrication system and raise the pressure.

After a major overhaul, if the engine oil pressure is too high, it is often due to the small fit clearance of the bearings (bearing shells) in the pressure lubrication section. The oil pressure of an engine that has been in use for a long time is too high, which is caused by the clogging of the fine oil filter. It should be cleaned or replaced.

1.4 Improper adjustment of the pressure-limiting valve

The oil pressure depends on the magnitude of the spring force of the pressure-limiting valve. If the adjusted spring force is too large, it will cause the pressure inside the lubrication system to rise. The spring force of the pressure-limiting valve should be readjusted to bring the oil pressure back to the specified value.

The oil pressure is too low

Low oil pressure refers to the situation where the display of the oil pressure gauge is lower than the specified value.

2.1 Wear of the oil pump or damage to the sealing gasket

The internal leakage of the gears inside the oil pump increases due to wear, causing the oil pressure to be too low. If the sealing gasket at the junction of the oil strainer and the oil pump is damaged, it will cause insufficient oil suction from the oil pump and a decrease in oil pressure. At this point, the oil pump should be inspected and repaired, and the gasket replaced.

2.2 The oil volume sucked into the oil pump has decreased

If the oil level in the oil pan decreases or the oil pump's strainer is clogged, it will reduce the oil pump's suction capacity, resulting in a drop in oil pressure. At this point, the oil level should be checked, engine oil added and the oil pump strainer cleaned.

2.3 Large oil leakage

If there is leakage in the lubrication system's pipelines and the wear clearance at the crankshaft or camshaft is too large, it will cause an increase in the leakage of the lubrication system, resulting in a decrease in the oil pressure. At this point, it is necessary to check whether the lubrication pipeline is cracked and adjust the fit clearance of the bearings at the crankshaft, camshaft and other places as required.

2.4 The oil filter or cooler is clogged

As the oil filter and cooler are used for a longer time, the accumulation of mechanical impurities and other contaminants will reduce the cross-sectional area through which the oil flows, and even clog the filter and cooler, resulting in a decrease in the oil pressure at the lubrication points. At this point, the oil filter and cooler should be inspected and cleaned.

2.5 The viscosity of the engine oil is too low

If the atomization of diesel injection is poor, causing diesel oil droplets to enter the engine oil, the viscosity of the engine oil will become thinner and the oil pressure will drop. If water gets into the engine oil, it will turn milky white, causing the viscosity of the oil to become thinner and resulting in a drop in oil pressure. Incorrect selection of engine oil grade, such as using winter engine oil in summer, can also cause a drop in oil pressure due to its low viscosity. If the engine temperature is too high, it will cause the viscosity of the engine oil to decrease, resulting in a reduction in internal frictional resistance, an increase in leakage in the lubrication system and a decrease in pressure. At this point, the fuel injectors should be calibrated, the leakage points should be inspected and repaired, the appropriate grade of engine oil should be selected as required, the cause of the excessively high engine temperature should be identified and repaired.

2.6 Improper adjustment of the pressure-limiting valve

If the spring force of the pressure-limiting valve is too small or breaks due to fatigue, it will cause the oil pressure to be too low. If the pressure-limiting valve (due to the influence of mechanical impurities) does not close tightly, it will also cause the oil pressure to drop. At this point, the pressure-limiting valve should be cleaned and the spring adjusted or replaced.

2.7 The oil pressure display is too low

If the oil pressure sensor and the oil pressure gauge malfunction, the displayed values will be distorted, leading people to mistakenly believe that a lubrication system failure has caused the oil pressure to be too low. At this point, the oil pressure sensor and the oil pressure gauge should be inspected and replaced.

3. There is no oil pressure

No pressure means that the pressure gauge shows 0.

3.1 The oil pressure gauge is damaged or the oil pipeline is broken

Loosen the pipe joint of the oil pressure gauge. If pressure oil flows out, it indicates that the oil pressure gauge is damaged and the pressure gauge should be replaced. If the oil pipeline ruptures and leaks a large amount of oil, it will also result in no oil pressure. The oil pipeline should be inspected and repaired.

3.2 The spring of the pressure-limiting valve is damaged

The spring of the pressure-limiting valve is damaged, causing the oil pressure gauge to show 0. The spring should be replaced.

3.3 The oil pump is damaged

The oil pump has no oil pressure due to severe wear. The oil pump should be repaired.

3.4 The paper gasket of the oil filter is installed in reverse

When overhauling the engine, if not careful, it is very easy to install the paper gasket at the connection between the oil filter and the cylinder block in reverse. The oil inlet hole and the oil return hole will be connected, and the oil cannot enter the main oil passage, resulting in no oil pressure. The paper gasket of the oil filter should be reinstalled.

In addition, if the oil level is insufficient or the spring of the bypass valve is deformed, lacks elasticity and does not close tightly, it can cause the pointer of the oil pressure gauge to swing back and forth. Qualified oil should be added and the bypass valve should be inspected and repaired.

References

Compiled by Jiao Fuquan and Liu Hongbing. Analysis and Handling of Faults in Construction Machinery, People's Communications Press, 2001.1

2. Du Haitao, "Practical Guide to the Use and Maintenance of Earthmoving Machinery". Construction Machinery and Maintenance, 2002. 9

Engineering Construction Machinery 2005.NO.12