Bill, As you are gathering evidence. Crankcase vacuum, say over about 5" of water, has the potential to pull unfiltered air into the engine.
The air (and silicon dirt) would have to work its way past some engine seal, but it's a valid proposal. See, another good reason to hope somebody here can present oil analysis results eventually.
Exactly what I'm working on.
Bill, BillL's note also offers a good reminder regarding your current test....seal the catch bottle to the hose if you're running an evacuator tap with the separator. If you don't, it will pull air into the system at the neck of the catch bottle and route it to the evacuator tap on the exhaust. That flow will oppose normal drainage to the catch bottle and skew the test results.
Everyone...don't get confused about discussion of vacuum in the context of Busch's objections. We are not all running identical systems. There are many choices in use:
1. Breather to overboard drain point....the usual way.
2. Breather to separator, air outlet to overboard, liquid output to catch bottle. Reduction in belly mess.
3. Breather to separator, air outlet to overboard, liquid output to engine sump. Reduction in belly mess and overall oil consumption.
4. Breather to separator, air outlet to exhaust via a reed valve, liquid output to sealed catch bottle. Reduction in case pressure and overall belly mess.
5. Breather to separator, air outlet to exhaust via a reed valve, liquid output to engine sump. Reduction in case pressure, overall belly mess, and oil consumption.
Only (4) and (5) reduce case pressure, i.e. pull a vacuum in the case. The Busch video example was probably a (2).
BTW, systems with a case evacuator (4 & 5, reed valve to the exhaust) reduce the temperature at which water vapor would condense. If you assume a pressure reduction of 3"Hg (it varies, but that's a fair average), the boiling point reduction would be a bit more than 5F. Put another way, running a case evacuator with your separator reduces the chance of condensing water and returning to the sump.
If your separator/evacuator system is operating in a hot area of the engine compartment, you further reduce the chance of condensing water. Conversely, if your GA clunker has a big leak in the rear baffle flap seal so the separator is operating in a jet of nice cool air, yep,
you have a condenser.