General troubleshooting methods for Dongfeng Cummins engine

1. The water temperature is low and the water tank overflows

What does the water tank overflow mean?

When the piston is compressed upward or the combustion breaks out, the high-pressure gas in the cylinder rushes into the water channel from the damaged cylinder gasket, causing a large amount of water to overflow from the water filler cover overflow pipe and the breather valve. In severe cases, water is sucked in again with the intake stroke. Cylinder, to stop the engine, of course, the coolant will be reduced accordingly.

Reason

• The cylinder head is not flat, the tightening torque of the cylinder head bolts is insufficient, or the used bolts have been extended and deformed and the cylinder gasket cannot be compressed.

• There are defects such as blisters and cavitations in the water channel adjacent to the cylinder block or cylinder head and the combustion chamber, causing permeability.

• When the temperature is too high, the sudden addition of cold water will cause cracks in the water passage of the cylinder block or cylinder head, which will cause high-pressure gas to enter the water passage.

Diagnosis and treatment methods

When water vapor overflow occurs, first check whether the cylinder head of the air compressor is leaking.

If the air compressor has no fault, the oil can be cut off for each cylinder in turn to determine whether the cylinder head gasket is damaged.When carrying out this inspection, the water tank cover should be opened for observation. When the oil-cut cylinder does not work, he water tank no longer overflows, and the white smoke from the exhaust pipe is also improved. It indicates that the cylinder head gasket of this cylinder is damaged and should be repaired and replaced in time.

If there is no damage and no traces of air leakage when inspecting the cylinder head gasket, it is necessary to find out whether there are corroded holes, and if there are any, repair them.

2. Diagnosis and treatment of sudden low oil pressure

The oil pressure suddenly drops during use, and the oil gauge needle suddenly points to the zero position, which is one of the common faults in maintenance for the engine that has been used for a long time. But the sudden point of the oil pressure gauge needle to zero does not necessarily mean that the oil pressure suddenly drops to zero.

Reason

1) The oil meter and wiring are faulty.

2) The oil sensor plug is faulty.

3) The oil pump is damaged.

4) The camshaft bearing comes out, leaking engine oil.

5) The lubricating oil pipes of the fuel injection pump, supercharger, air compressor, etc. are broken.

6) The oil pressure limiting valve is stuck in the open position and the pressure regulating function is lost.

Diagnosis and treatment methods

• During the operation of the car, if the oil pressure drops suddenly, stop and check immediately to prevent major accidents of shaft burning and cylinder scoring due to lack of oil.

•  First check that there are traces of a large amount of inorganic oil leakage on the outside of the engine. If there is, it means that the oil pipeline, filter cover, etc. are broken or the drain plug of the oil pan is loose and the oil leaks, and it should be repaired in time .

• If there is no trace of a large amount of oil leakage from the outside, check whether the connection line from the oil machine pressure gauge to the sensing plug is intact, and whether the meter and the sensing plug are in good condition.

• Draw out the oil dipstick to check whether the amount of oil is sufficient.

• Loosen any oil pipe joints outside the engine, use a starter to drive the crankshaft to rotate, and check the oil supply. If the oil flows out, check whether the oil pressure limiting valve is stuck in the open position.

•  The crankshaft is rotating, listen to the noise on the side of the camshaft. If there is a noise, further check whether the camshaft bearing has come out and eliminate it in time.

 Diagnosis and treatment of low oil pressure

After the engine is cold-started or during normal operation, the oil pressure appears to be lower than the normal working pressure. When the alarm indicator is flashing, it is usually caused by an oil system failure and should be shut down for processing.

Reason

• The oil number is not up to the regulations, which causes the oil viscosity to be too low and the pump oil pressure drops.

• The engine oil has deteriorated or there is water in the engine oil.

• Insufficient oil capacity.

• The engine is overheated and the oil becomes thinner, resulting in lower oil pressure.

• The oil collector is clogged, and the oil intake is reduced and the pressure is too low.

•  The coarse oil filter is too dirty and the bypass valve is damaged, making it difficult for the oil to enter the main oil passage.

• The oil pump is severely worn, and the gear meshing gap or the pump cover gap is too large, causing the pump oil pressure to drop.

• The pressure limiting valve spring is too soft to make the main oil passage pressure lower than the specified value.

• The long-used engine crankshaft main bearing clearance and connecting rod bearing clearance are too large, and the camshaft bearing clearance is too large, resulting in low oil pressure.

• The oil pump safety valve has been used for too long, the valve and the valve seat are worn out and the seal is not sealed, or the spring is too soft, so that when the oil pump is working, a large amount of oil will flow back through the safety valve, making it difficult for the main oil passage to build up normal pressure.

• The oil radiator is blocked and the bypass valve fails, which makes the oil pressure too low.

Diagnosis and treatment methods

• When the engine is running, if the oil pressure is too low, stop in time. After about 5 minutes, check whether the oil level of the oil pan is lower than the specified value. If it is lower than the lower mark of the oil gauge, add oil of the same brand at any time.

• Pull out the oil dipstick to check whether the oil has deteriorated and moisture. If the engine oil deteriorates, it should be replaced, and the engine oil passage and filter element should be cleaned; if there is water in the engine oil, the source of the water should be found out to remove it, and the new engine oil should be replaced.

• If the engine oil of suitable viscosity is not changed in time according to the seasonal changes, the low-quality engine oil is mistakenly added, or the engine oil that does not meet the qualified grade, it should be replaced in time with the engine oil suitable for the seasonal viscosity or grade.

• If the engine is overheated during use, the drop in oil pressure may be caused by the oil becoming thin due to excessive temperature. In this case, you should lower the engine temperature first, and then start the engine after the oil cools, and the oil pressure can return to normal. Therefore, in use, special attention should be paid to whether the temperature of the engine and the heat dissipation of the oil are good.

• Check whether the oil filter core is clean and whether the bypass valve is unblocked. If the filter element reaches the replacement cycle or is too dirty, it should be replaced or cleaned in time, and ensure that the bypass valve is not stuck.

• Check whether the filter of the collector is too dirty. The filter collector that has not been maintained for a long time, due to excessive glue sticking to the mesh cover, seriously affects the oil passing rate and reduces the oil supply pressure, and should be cleaned and maintained.

• Check whether the lubricating oil channel is blocked by sediment, and unblock it during maintenance.

• Check whether the pressure limiting valve spring is too soft and whether the valve is too worn. If the valve is worn normally, check whether the spring force is insufficient. The spring can be removed and inspected on the test bench. In general, it is not allowed to adjust at will. If the valve is worn out and leaks oil, it should be replaced as a whole.

• Finally, check whether the clearance between crankshaft bearings, connecting rod bearings and camshaft bearings is too large.