Question - Checking Engine Oil Level

I have been ?burping? the engine before the first flight each day and then checking oil level prior to starting the engine. TT is 77 hours with almost 30 hours since oil change. Engine is not using any oil as checked per above procedure.

Today I decided to check oil level at the end of the flight and was surprised to find oil level in the sump tank to be below the end of the dipstick and completely out of range of the flat marking on the stick. I thought the oil tank would have held the entire quantity of oil for some period of time before slowly bleeding back through the oil pump and into the crankcase.

Am I over-thinking this or is it normal to not have a full oil tank at the end of a flight?

That's normal.

All the oils is in the engine, not in the dry sump tank where you check it. That's the reason for "burping" the Rotax-- when it burps it's pushing air into the sump tank, not oil.

I'm one of many who check the oil AFTER a flight. Although it's more difficult to pull the prop through against the higher compression (stopping for a few seconds when you feel compression speeds things up) the engine will usually burp after 8-10 blades versus 20 or more when it's cold. If you check after a flight, and there's no puddle on the floor when you start the next one, all the oil is still where it's supposed to be.

Wayne 120241/143WM

After a flight, a small portion of oil remains within the engine crankcase. "Burping" the engine serves to force this residual oil (maybe 1/2 pint?) back into the oil tank. As a result, you are then able to more accurately measure the total amount of oil available to the engine. On my RV-12, an "un-burped" engine has an oil dipstick reading just below the ADD OIL line. After "burping", the oil dipstick reading is just below the FULL OIL line. The "burped' level varies somewhat depending upon the engine oil's temperature, viscosity, and your manner of "burping". Also, you will cut down on the number of prop revolutions it takes to "burp" the engine if you briefly pause at the top of each cylinder compression to better allow the piston blow-by to pressurize the crankcase thus forcing the residual oil back into the oil tank. It's a Zen-kinda thing.

There is much written in this site on this subject, try SEARCH for more info.

I'm totally in agreement with David and Wayne - burp/gurgle post flight as it's a much more efficient process when hot and do it slowly with pauses on compression.

Pre-flight, if it's above the minimum without burping/gurgling, then you're good to go - if it isn't burp/gurgle it again and add oil if necessary.

There is some bleed back into the engine from the tank when it's not flying and the amount varies between aircraft installations depending on the relative heights of the engine and oil tank.

I flew again today and did the burping trick before and after the flight. You guys are correct that the oil needs to be burped back into the tank even immediately after shutdown in order to get an accurate measurement of oil quantity. As it turns out, my level hasn't changed in 30 hours of operation. Oil is fairly clean too. Pretty good...

Piper J3 said:

I flew again today and did the burping trick before and after the flight. You guys are correct that the oil needs to be burped back into the tank even immediately after shutdown in order to get an accurate measurement of oil quantity. As it turns out, my level hasn't changed in 30 hours of operation. Oil is fairly clean too. Pretty good...

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With the Rotax you will find the only time you put oil in is when you change the oil.