Oil Catch Can

[skyblue]

I was thinking about adding a catch can but I don't know whether it's worth the effort. What am I keeping clean, it looks like the vent exits past the throttle body, so any dirty crap would be exiting on the inlet valve and cylinders?

Looking at this diagram doesn't help me much, what's to stop the blow by from simply going up the breather hose? Why does there even need to be a breather hose considering blow by pressure would exit by virtue of pressure wanting to escape? I can't really understand how air being pulled through the air intake doesn't also pull air from the breather hose. I would have thought it would be easier for it to exit from the breather than the vent because the vent has a valve on it. I feel like a one way valve on the breather only allowing air in would be a good idea.

Could I put a filter on the breather hose and disconnect it from the air intake, so that if oil vapor does make it up there it won't flow through the butterfly and MAP?

Appreciate any wisdom.

[foama]

Mine has a catch can! It was inserted in the rubber ventilation hose exiting the PCV valve.

It collects about 0.6L fluids between oil changes in the cold season, that is when it freezes or snows outside. The collected fluid is a mix of water and oil, mainly water. Collecting keeps the intake and intake valves clean.

In the warm season it only collects a tiny amount of oil without any water, not worth the effort.

My recommendation: If it never freezes where you live, you will not need one. For example maybe you could use one in Hobart (43° latitude), but never need one in Brisbane (27° latitude).

[skyblue]

Cheers.

Can anyone explain, when blow by occurs what prevents the blow by from exiting through the breather hose?

In my head I imagine that some of it goes out through the PCV valve (and therefore cannot return) and some goes up the breather hose. During the exhaust stroke the blow by that snuck up the breather hose gets pulled back into the crankcase by the vacuum and the fact that it can't come in through the PCV valve. This process ensures the blow by never sneaks out of the breather meaning the gas never comes out in front of the butterfly and map?

However when the blow by gas is trapped on the outside of the PCV valve it's sitting in the intake (on the engine side of the butterfly and map), which would push the air already there out a bit, would this likely contaminate the MAP sensor over time considering it's on the engine side of the butterfly valve?

Am I on the right track?

I wonder how much blow by gas gets pushed into the intake space and how far back it goes toward the throttle body or if it even gets close.

[foama]

Cheers.

Can anyone explain, when blow by occurs what prevents the blow by from exiting through the breather hose?

In my head I imagine that some of it goes out through the PCV valve (and therefore cannot return) and some goes up the breather hose. During the exhaust stroke the blow by that snuck up the breather hose gets pulled back into the crankcase by the vacuum and the fact that it can't come in through the PCV valve. This process ensures the blow by never sneaks out of the breather meaning the gas never comes out in front of the butterfly and map?

However when the blow by gas is trapped on the outside of the PCV valve it's sitting in the intake (on the engine side of the butterfly and map), which would push the air already there out a bit, would this likely contaminate the MAP sensor over time considering it's on the engine side of the butterfly valve?

Am I on the right track?

I wonder how much blow by gas gets pushed into the intake space and how far back it goes toward the throttle body or if it even gets close.

Right-oh mate. Let me try to answer.
There is nothing preventing blowby from exiting the crankcase through the breather hose, but unless the engine is totally worn out there will usually never be enough blowby to make that happen. Probably some air will be drawn in to the crankcase through the breather hose. Blowby is extremely unhealthy, and therefore it is processed as part of every emission system. Blowby exits the crankcase through the PCV valve into the intake manifold where vacuum is greatest. Blowby is subsequently burnt together with the other gasses during combustion. The PCV-valve actually has a regulating mechanism with a spring inside it. The higher the pressure difference, the smaller the channel passing gasses through it. Look it up on the net.
See: https://en.wikipedia.org/wiki/Crankc...ilation_system
It is one part of the normal emission control system on any car. The PCV valve increases its restriction when the pressure difference between outside atmosphere versus intake manifold vacuum is high, and opens a bit more when the pressure difference is low.
The breather hose is there to ensure there is no vacuum or too low pressure inside the crankcase, it ensures regular outside atmospheric pressure inside the crankcase. A vacuum inside the crankcase would remove most of the oil film on the cylinders, and that is most undesirable because it can easily kill an engine. Since this is not a one-cylinder engine, we can assume the pressure inside the crankcase remains more or less constant within close limits in the running engine. I suppose that explains your questions.