market dynamics
What is the situation of oil gushing in vent pipe after motorcycle flameout? Moderation is best
Release date:2022.04.26

Recently, some car friends asked, his CG model access car after continuous driving, engine flout for a while, will continue to gush oil from the ventilation tube above the transmission, after a while to stop, but this situation will not occur when driving, what is the reason?

Strictly speaking, not all models are prone to this condition, but the CG125 motorcycle is more prone to this condition due to the special structure of the engine crankshaft chamber.

With this hidden danger, why does the engine have a snorkel? To understand the causes of this phenomenon, it is necessary to understand the structure of the gearbox.

First, the role of the ventilation tube. The transmission vent of the four-stroke motorcycle engine keeps the pressure of the crankshaft chamber connected to it at atmospheric level, thus reducing the resistance of the piston when it moves down. At the same time, it will also emit heat from the gearbox, which is designed from the Angle of reducing resistance and improving power.


The vent is located at the top of the gearbox, the farthest distance from the oil surface of the oil pan, and there are multi-layer wall barriers. The gas must be discharged to the outside through the bending channel, and the vent is not connected with the oil channel. From this point of view, it is generally not flooded with oil.

Under normal circumstances, the air passage between the crankshaft chamber of the gearbox and the atmosphere is smooth. When the piston moves down, the pressure in the crankshaft chamber increases, and the gas is discharged from the ventilation tube to the engine. While maintaining the pressure balance inside and outside the gearbox, it also takes away heat and plays a role in heat dissipation.

When the oil level of the oil pan is too high, the oil and the crankshaft chamber separator jointly close the ventilation duct, and under the action of the internal air pressure, the oil pressure of the machine to the ventilation duct, so as to flow out of the ventilation pipe.

This phenomenon will not stop until the internal pressure is reduced or the oil level is low.

But why does this phenomenon not occur when the engine is running, but only when the engine is stopped and turned off?

This is because in the operation of the engine, part of the oil is pressed into the oil passage to lubricate various parts, so the oil level decreases, the ventilation passage will not be closed, and the oil can not be discharged out.

Even after the ventilation duct is closed by the oil surface, only when the temperature is high and the air pressure is large enough will the oil be filled with the ventilation duct and discharged out.

Therefore, the root cause of this situation is more oil, or oil into the water or gasoline to increase the total amount. In this case, we must pay attention to observe the oil window in the stationary state of the parking to see if it is within the specified scale line. At the same time, when adding oil, it is also necessary to add quantitatively, not the more the better.