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.
I can only speak for myself (about to install catch can), all that it does (when installed with no modification) is improve the engine's ability to separate oil from crankcase gasses. I'm tired of fouling plugs. The system in many modern engines is not sufficient, and engineers have their hands tied to fix it.
The original design was to filter vent the crankcase to the atmosphere. Since there are hydrocarbons in the crankcase gasses, they are considered pollution. The solution is to vent those gasses into the intake to be burned. If they are vented into the crankcase to be burned, you need a source of filtered fresh air to replace it in the crankcase. If you were to put a filter to the atmosphere, it would make a path for air to enter the engine and find its way to the intake without being "seen" by the MAF, throwing off the A/F mixture, so it's drawn after the MAF.
From what I understand, nothing that is strictly emission controls can have scheduled maintenance in order to continue functioning, so this is why Chevy Performance makes catch cans for new cars (like the new Camaro), but is not allowed to install them at the dealership.
So, this is why the throttle body gets so dirty so often. This is why (I think) my plugs don't last that long. I usually have a think film of oil in the resonator when I take it off. The baffle system isn't effective at separating oil and air, and the catch can will improve this.
It doesn't help that the intake vent is orificed and can clog, and the tube makes two 90-degree bends, one of which is behind a heat shield that cannot be removed without breaking it (hence the dremel modification to the intake to get to the port).
If you don't see oil in your resonator, and don't hear lots of hissing gasses under the intake heat shield, there's no reason to modify your vehicle (unless you plan on off-roading a lot or doing something to splash a lot of oil around).
I'm ready to install a catch can, and even modify it to vent gasses to the air because I'm tired of dealing with the problems its giving me now that I'm over 150k miles.
Short answer: Catch can does what the valve cover baffles try to do, but do a better job. They can't be put on the car because GM can't put a pollution control device on the truck that requires maintenance (draining the can).
It also doesn't help that the oil that isn't supposed to be there softens the vent tubes and makes them leak easily.