The VariEze 0-290’s initial propensity for spewing oil vapor was calmed by repositioning the case breather outlet to a welded fitting in the mag hole cover plate. I had been warned of significant wet vapor expulsion from the stock case vent by the prop flange and they were right. But now the oil laden vapor loses some energy coming up into the accessory case before coming out the upward directed 90 in the mag hole cover plate. From there the exit hose crosses over the accessory case into a custom air/oil separator at the upper firewall, then aft under the pushrod tubes to the aft cowl opening.
The air/oil separator is made from an aluminum automotive air conditioner “dryer” I believe it's called, one of dozens discarded in the corner of a friend’s a/c shop. I cut it open and cleaned it out and fitted it with a middle baffle plate and some stainless steel mesh. If I had known exactly where I was going to mount it on the upper firewall I would have shaped it slightly differently. It already had one ¾ inch tube outlet at a good location and another was welded on for the breather hoses.
Another smaller tube is welded on the bottom corner of the separator with a gravity-return tube for the condensed oil. While the tube should be suspect of several irrational design flaws, including the fact that it would have equal and opposite pressure on both ends during engine operation, it has none of the negatives that I expected, and works splendidly probably due to an overall bow to gravity. The return fitting for this drain/return tube into the case is just above the case/sump joint where it does not spew diabolical green alien acid on the cam. I appreciate that concern and have taken defensive steps but have noticed several other things to actively pursue and defend against, like not running out of fuel or into the ground, and just let this contraption do what it does so well with a cleaner and dryer aircraft posterior. It is free flowing and retains the same diameter of the standard case vent through the entire length of the tubing and separator. The “clear” tubing adheres to the strict direction in the plans
This air/oil separator is robust and could (and has been) mounted in many different locations. It was especially useful during the early engine operation, although the oil vapor floating around the aft end of the plane in flight revealed many things about how air does and doesn’t follow the rules back there. Very interesting and enjoyable, especially once I got to where I could control the blowby. And now there is no reason to remove it
A side note - early on, breaking in the steel cylinders and chrome rings, a sage A&P that helps with engine stuff every annual stated/suggested that everything else being equal, the rings and cylinders would seat and the blowby would calm down on its own at about 100 hours. He was exactly right.
