Fred,

 

Here is some useless information:

 

1. I have high oil usage (1 qt per 6-7 hrs) and no evidence of blowby (sometimes spelled: blow bye bye).

 

2. I measured crankcase pressure by tapping a port into the filler cap and hooking it up to the pitot of an airspeed indicator using both lower cowl and cockpit static (adjusted for cockpit low pressure via an altimeter) as ambient pressure and found no crankcase positive pressure.  BTW, I have permanent "pitot, static" lines plumbed into the engine compartment so that I might measure a variety of pressure differences (technically called "from hither and yon").

 

3. I used a "old mechanic's tale" method of routing the breather line as high as I could before it descended to the exiting overflow tube.  This allows condensing oil to drip back into the engine vent opening.  I use a clear tube for this so I can look at greasy paths after the flight.  Uh, I don't see much difference but I really don't have any room for reaching much height from the engine vent port before the line descends.

 

4. I am suspicious of the 45 degree aft facing cut in the vertical vent tube as it is in the engine cooling air exit stream and might be causing suction?  But, see #2.  Perhaps I should turn it around?

 

5. I love my little hummer of an engine - I just don't know why oil is, uh, pitched overboard.  ECI Cermi-nil Cylinders with fancy rings, some of which are plasma coated (hardened more than the face of a trollop waiting for her due).

 

6. Arrrrrgh.

 

Grayhawk

 

 

I wrote earlier that my IO-550 was dumping oil out the air oil separator, and with some fiddling with the plumbing, it appeared I solved the problem.   High power climbs yielded no oil loss.  Ground tests showed no blow by.  Problem solved. 

Wrong. 

New hypothesis: It appears that the losses occur during cruise, not take off and climb.   I climb at 160 knots, cowl flaps open.  I cruise at 200-220 IAS, cowl flaps closed.  The ram pressure at cruise is 1.5-1.7 times greater than in climb. 

So the current hypothesis is that the crankcase could be pressurized by external air pressure and the air flow through the crankcase carries oil overboard.

A bit of research suggests checking the crankshaft nose seal and the oil filler cap. 

Has anyone had problems with Continental crank case pressurization?  What have you learned? 

My next step is to pull the breather tube off the air oil separator and use some low pressure compressed air to pressurize the crankcase (engine off) and see if I can find some leaks.   The next level of complexity is to put a tube up the crankcase breather, connect to an airspeed indicator in the cockpit to check pressure, and go flying and see what happens.

Other suggestions or other experience that might help guide us through this maze?

Thanks in advance,

Fred Moreno