- Feb 5, 2008
Properly venting the crankcase is important and easy to mess up. On my former Sonex the vent tube was a 1/2" diameter tube the ran over the top of the engine and down to the bottom of the cowl. I didn't like that it was dumping oil all over the bottom of the plane so I extended it with a smaller tube down to the bottom of one gear leg. Next flight my engine blew a ton of oil out the prop hub and all over the engine and cowl....what a mess.IF you do not vent the crankcase in a low pressure area ( I do it how VW does it). I run the crankcase vent tube to the inlet of the carb, you will still have a little oil leak around the oil seal at the prop hub
I eventually made an oil separator that worked well to condense the oil vapor without creating back pressure in the crankcase.