Exhaust coming out from vent tube?>

[7981GS]

The main air filter also ensures that any air sucked into the crankcase is filtered as well.

It also creates vacuum to pull the crankcase by-products out.
That is why it is important to mount the vent tube under and behind the engine to draw them out if you do not run it into the airbox.
It is then referred to as a "draft tube"

Draft tube:
From 1928 until the early 1960s, car and truck petrol engines vented combustion gases directly to the atmosphere through a simple vent tube.
Frequently, this consisted of a pipe (the 'road draft tube') that extended out from the crankcase down to the bottom of the engine compartment.
The bottom of the pipe was open to the atmosphere, and was placed such that when the car was in motion a slight vacuum was obtained, helping to extract combustion gases as they collected in the crankcase.
The vacuum was satisfied by a vent, typically in the valve or valley cover, creating a constant flow of clean air through the engine's air volume.
The oil mist would also be discharged, resulting in an oily film being deposited in the middle of each travel lane on heavily-used roads.
The system was not positive though, as gases could travel both ways, or not move at all, depending on conditions. (Most modern diesel engines still use this type of system to dispose of crankcase fumes.)

Daniel

[AJ]

It also creates vacuum to pull the crankcase by-products out.
That is why it is important to mount the vent tube under and behind the engine to draw them out if you do not run it into the airbox.
It is then referred to as a "draft tube"

Draft tube:
From 1928 until the early 1960s, car and truck petrol engines vented combustion gases directly to the atmosphere through a simple vent tube.
Frequently, this consisted of a pipe (the 'road draft tube') that extended out from the crankcase down to the bottom of the engine compartment.
The bottom of the pipe was open to the atmosphere, and was placed such that when the car was in motion a slight vacuum was obtained, helping to extract combustion gases as they collected in the crankcase.
The vacuum was satisfied by a vent, typically in the valve or valley cover, creating a constant flow of clean air through the engine's air volume.
The oil mist would also be discharged, resulting in an oily film being deposited in the middle of each travel lane on heavily-used roads.
The system was not positive though, as gases could travel both ways, or not move at all, depending on conditions. (Most modern diesel engines still use this type of system to dispose of crankcase fumes.)

Daniel

That's very cool, Daniel. I hadn't really thought about it before. On my airplane, the "draft tube" exits underneath the cowling in a low pressure area. The tube itself is angled to create a venturi draft pulling gases out of the tube. This leads to an "oily belly" as the oil condenses on the bottom of the fuselage, and this is the main reason airplane owners use the oil scavenger system I mentioned in my previous thread. It also points out how much engineering, even of the "trial-and-error" kind there is in modern vehicles, and how aware we need to be as we modify these machines.

I always assumed feeding the crankcase vent back into the air cleaner (plus the PCV valve) was for environmental concerns, but it had the added benefit of getting oil off the roads, which are much cleaner today than I remember as a youngster.

Thanks for posting that! Cheers.

[7981GS]

It also helps to draw the pressure out of the crankcase allowing the engine to rev quicker.
And aids in piston ring sealing. I.E.: the piston is allowed to send pressure down after combustion with less pressure pushing back up.

Daniel