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