I had some interesting discussions with a well-respected member, who for now, will remain anonymous. We had a long discussion about catch cans and their usefulness. I’ll try to summarize:
All engines make oil mist, some more than others. It is perceived by several experts that this is present in nearly all engines, but more of an issue on some designs. There’s no real way to know which design is more prone other than experience. PCV design and placement also plays a role.
However, in the types that do collect this oil mist in the PCV system, the trappings can actually tell you about the composition of your oil, and this is a current test I’m running on my 3.5 EB (about 2 ounces total collected so far). When the oil is analyzed, if the additive concentrations appear much higher than the UOA of the oil, this tells you that the base oil is evaporating rapidly and that the mist is therefore more concentrated with the “heavier” additives. If the composition is roughly the same as the VOA, this tells you all the oil in the PCV system is due directly to the mist, since it is collecting the lighter base oil and the heavier additives at the same rate.
Obviously in winter there will be some condensate collected, but my source did not feel that fuel will be a considerable amount, simply because they’re too light to condense even in the PCV system, or at least after the system has been warmed during operation.
And, for those who think “lots” of condensation happens because the can is aluminum, at least on my truck I only made the mistake once of trying to check the catch can directly after a drive- it made my hand pink and felt like I had touched a hot pan; I’d bet it was every bit of 160*F or more. Remember, the air passing through the PCV is heated by the block at ~210* and the oil at nearly the same, so after a long enough time, any temperature delta will be nil. That means probably 200*+ during Highway operation especially in summer.
Will let everyone see results when I get the catch can UOA results.