A catch can needs to be emptied of its hazardous waste on a regular basis. Our AOS needs ZERO maintenance. A catch can emits the unpleasant smell of the crankcase fumes. Our AOS doesn't smell and is emissions friendly. Most catch can systems end up leaking or spewing oil in/on your engine bay while our AOS keeps everything clean and tidy.
Also with oil not being removed from the pan, there is no worry of running low on oil whatsoever...also I don't personally know about the smell issue and maybe its more directed at VTA cans, but it's a good point nonetheless.
An regarding the moisture theory there is this:
3. What causes the yellow gunk? This is a mixture of oil and water. Usually when the water in the engine heats up it vaporizes and makes its way out the breather system. If it stays in vapor form it will make its way out the top of the AOS and into the intake. We have found from our cold weather customers that condensation is occurring inside our AOS as it is colder than the engine. This condensation is mixing with the oil in the AOS causing the yellow gunk. To fix this issue we have made a cold weather version that incorporates a heater inside the AOS to keep the AOS at the same temperature as the engine. With them being the same temperature, condensation will not occur leaving the water vapor to flow out the top of the AOS and into the intake system.
Now these replies are from a STi forum, but the physics and functionality are the same
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