3.5 Crankcase Ventilation System description, from the 2005 Service Manual:
A crankcase ventilation system is used to consume crankcase vapors created during the combustion process instead of venting them to the atmosphere.
Fresh air is supplied through a filter to the crankcase, the crankcase mixes the fresh air with the blow-by gases and then passed through a positive crankcase ventilation (PCV) orificed tube into the intake manifold.
The PCV orificed tube restricts the flow rate of the blow-by gases using a 2.5 mm (0.098 in) orifice located in the camshaft cover tube. If abnormal operating conditions arise, the system is designed to allow excessive amounts of blow-by gases to back flow through the crankcase ventilation fresh air tube into the air cleaner resonator in order to be consumed by normal combustion.
As far back as I can remember, engine were vented. Prior to the PCV Systems, the vent was nothing more than a cap attached to the valve cover. It was removable for cleaning. I'm sure that there is still a need to vent the engine, probably to prevent pressure buildup that could cause blowby. If you were to block the exhaust port that goes to the intake and attach something to the inlet side, it might create breathing problems.
The throttle body plate never closes fully. It is spring loaded to a partially open, default position, to provide airflow at idle.
I need some help to get my head wrapped around the purpose of a "catch can" on a stock, daily driver vehicle. I understand that vehicles with high compression/high horsepower engines, in race mode, would develop excess internal pressure, and would need a method of capturing the venting.
On a stock engine, such as we have in our trucks, the crankcase venting is accomplished by fresh air entering the engine through the resonator, circulating in the engine, and exhausting, as a vapor, into the intake, where it mixes with the intake air and passes through the engine. Most of the time, the intake will be warm/hot enough to maintain the vapor state.
Now the part that I don't understand. It appears that a "catch can" is a sort of filter that is attached to the crankcase vent exhaust port and either open to atmosphere or routed back to the intake manifold. The vapors are routed through this "catch Can" and the resulting liquid that accumulates inside is periodically emptied out.
Why would this be considered a viable alternative to a properly operating OEM crankcase vent system? I have seen pictures of "catch can" setups, where guys are showing filter bowls with liquid in them and claim that they have "saved" their engines from disaster. To my understanding, they are only routing the normal vapor, from the engine, to a cool area where it condenses into a liquid. That's what happens when you cool a vapor. If it had been allowed to follow the OEM path, it would have been consumed in the engine.
Someone please explain what I am missing here. It's a big subject over at C'Fans, where a lot of guys are chomping at the bit to install a catch can on their 2015 Colorados/Canyons.
Well, with millions of vehicles operating without these "catch cans", and a lot of them having several hundred thousand miles, it seems to be a relatively few people actually need one. It appears to be a bandaid fix to use instead of repairing the OEM vent system. I'm still not understanding, if this is such a great feature, why it isn't in widespread use, and why would one want to install this on a brand new engine?
Maybe I'm still missing the point. We aren't talking about a "mass" of oil flowing through the vent system. Of course if you condense the vapor, in a container (catch can), over a period of time, it will appear excessive, when in reality, it doesn't amount to much. If an excessive amount of oil was being lost through a properly operating vent system it would show up as a loss on the dipstick and there would be complaints.
On a high mileage engine, worn rings or valve seals probably contribute more to plug fouling than vent vapors.
I'm not sure why the vent vapors would be causing excess throttle body problems. The vapors go to the intake manifold, thereby bypassing the throttle body.
Okay I'm still in the learning mode. Do you have a link to the Chevy Performance catch can? Do you have pictures of the camshaft cover with the plates removed?
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