Engine Won’t Burp

Mirek Generowicz wrote:

In 500 hours of operation I have never managed to get a burp from my oil, no matter how many times I turn the propeller, even if I hold it at the peak of each compression.  I wonder if that is because the oil tank and cooler are both below the engine and the oil naturally drains back to t he tank.  Isn't the main purpose of turning the propeller to get the oil from the crankcase back into the tank?    

You could be right in your theory - perhaps the initial questioner might review his "proven oil tank location"

There are several reasons for hand cranking an aircraft engine befor flight;

In a Rotax 9 to get as much oil as possible back into the tank, so as to be able to get a measurement to establish sufficient oil or not for flight.

To "feel" for the "quality" of the engines compressions as an indicator of good "health" ( I would recommend at least 8 full rotations of the prop as compression may slightly improve asoil pressure/distribution occurs.)

Some relubrication may also occur, reducing the chance of a dry bearing surface/reduce engine ware.

Possibly helps with assessing prop condition/security and gear box/slip clutch condition.

Great exercise/cardio work out.

Have you given Lockwood a call and asked their thoughts?

If the oil tank is correctly mounted and the propeller correctly rotated and it won’t burp, the crankcase isn’t able to hold pressure. Could be cracked crankcase or a seal or o-ring is blown.

"Normal" installation on planes like the AirCam has the oil tank mounted lower than the sump outlet in the case bottom. Hence, those will empty all the oil back into the tank on its own accord without burping.