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Old 09-02-2017, 02:23 PM
jnmeade jnmeade is offline
Join Date: Mar 2013
Location: Iowa
Posts: 135
Default Why Burp Rotax 912ULS?

We've all been taught to "burp" the Rotax 912ULS to move the oil from the crankcase to the oil tank so that we can accurately measure the oil level. Here is a nice technical discussion of what happens.

In addition to moving the oil from the crankcase to the oil tank, some hold that "burping" enough blades also tests for hydrolock. Hydrolock seems to be a phenomenon that is very rare in a flat, opposed engine. I've never been taught or seen any emphasis on testing for hydrolock in a Continental, Lycoming, Franklin or any other flat engine I've flown, so I'm going to assume that testing for hydrolock is not a necessary reason to "burp" a Rotax 912ULS. If that is in error, please give me the reference so I can learn.

When we fly an IO360, we likely know that it will hold 8 quarts of oil and that it is required by the FAA to fly all day on 4 quarts. Many of us don't even put in 8 quarts, rather, we use 7. Many don't add oil until the dip stick shows 6 quarts or even 5 quarts. The Rotax 912ULS has a range on the dipstick that is acceptable for oil level. So it does not seem critical to have some maximum or close to maximum oil level.

The following assumes this is your aircraft, you are the only one flying it and you know the oil fill history. That means you added the 3 liters at oil change time and noted any other additions.

Now, you go out and check your engine cold. It is at or above the add mark. You know there is zero or some additional oil in the crankcase so if you "burped" it and transferred some or all of that oil to the tank, the oil level in the tank would be equal to or greater than the oil level you measured "pre-burp". In other words, in this example, enough.

We have established that the oil tank contains enough oil and we are reasonably sure since we manage the oil that it does not have too much.

Why burp?
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