Crankcase vent tube vacuum

[201Steve]

I remember reading some stuff about where the end of your breather tube is, relative to the cowl flap door. 
 

I am drawing some oil out but I don’t think it is from excessive blow by pressurizing the case bc the oil is staying pretty clean. I’m wondering if my breather tube is creating a vacuum. I don’t remember where it is most optimal… maybe shorten it so that the end of the tube stays behind the cowl flap door? What’s the consensus on location for the least amount of inadvertent vacuum from the slip stream in flight?

 

 

[Andy95W]

Unless you’re using significantly more than one quart of oil per 6 hours, that looks 100% normal for a Lycoming engine marking its spot.  Just put an old pie pan or cookie sheet under that spot and wipe it out when you change your oil.

Your breather is taking acids and other corrosive combustion by-products away from your camshaft, and it looks like it’s doing a nice job of it.

[PT20J]

Here’s mine. It looks to be a little closer to the exhaust cavity skin than yours. It drips a bit, too. That’s pretty normal. Engine is a 300+ hr factory rebuilt that gets about 12 hrs/qt. 
 

[201Steve]

5 hours ago, Andy95W said:

Your breather is taking acids and other corrosive combustion by-products away from your camshaft, and it looks like it’s doing a nice job of it.

Yeah, I’m not worried about it for any reason. Just being nit picky, and this topic has come up before. I’ve never thought of it as a positive though… interesting thought. I don’t know if I understand how it’s removing anything except oil with the same concentration of corrosive byproducts of combustion than the rest of the oil in the system, though. 

[carusoam]

Also check the whistle hole location, size, shape, orientation….

This is the hole that should break the suction caused by the tube in the slip stream…

Some have been replaced, and the hole got forgotten… or covered…

PP thoughts only,

-a-

 

[A64Pilot]

Actually a slight negative crankcase pressure is good, the pressure differential isn’t great enough to pull any extra oil out, you don’t want any pressure in the case.

https://dsportmag.com/the-tech/quick-tech-the-benefits-of-lowering-crankcase-pressure-part-1/

Not aircraft article, but it explains why zero or slight negative is desired, but as was explained earlier the whistle slot will break any vacuum if any existed.

If your concerned about an oily belly, run a lower oil level, mine stays at about 5.5 qts, any higher goes overboard or install an oil separator. a separator will help but won’t eliminate an oily belly.

We aircraft types have a tendency to overthink things, it’s just the nature of a passion.