Burping the Rotax

H. Paul Shuch is a Light Sport Repairman with Maintenance ratings for airplanes, gliders, weight shift control, and powered parachutes, as well as an independent Rotax Maintenance Technician at the Heavy Maintenance level. He holds a PhD in Air Transportation Engineering from the University of California, and serves as Director of Maintenance for AvSport of Lock Haven.

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Paul_G
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Burping the Rotax

Postby Paul_G » Sun Sep 01, 2019 7:26 pm

My procedure to check the oil level includes checking it when I finish a flight. When I arrive for another flight in a day or two, is it necessary to burp the Rotax and check it again? If there is no oil leaking, it should be good to go, correct? I'm wondering if it is necessary or can I just crank it up and go? What do you think?

Thanks in advance for your input.
Paul G
N400TL 2016 Sirius TL-3000
Chelan, WA (S10)

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Warmi
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Re: Burping the Rotax

Postby Warmi » Sun Sep 01, 2019 7:39 pm

Everyone seems to have different opinion on this but I remember what Bill Canino told me once and it made sense to me ... if you the only one flying the plane and if , when you come in in the morning, you don’t see a big puddle of oil under the plane then the oil is there right where it supposed to be.
Flying Sting S4 ( N184WA ) out of Illinois

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Re: Burping the Rotax

Postby TimTaylor » Sun Sep 01, 2019 8:33 pm

If I owned my own airplane and kept it in a locked hanger, that's probably what I would do.
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drseti
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Re: Burping the Rotax

Postby drseti » Sun Sep 01, 2019 8:57 pm

No, regardless of who's been flying the plane, if the oil is anywhere on the flat of the dipstick, there's no reason to burp the engine. But again, no matter who's been flying the plane, it is essential to check the dipstick before every flight.
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof H Paul Shuch
PhD CFII DPE LSRM-A/GL/WS/PPC iRMT
AvSport LLC, KLHV
fly@AvSport.org
AvSport.org
facebook.com/SportFlying
SportPilotExaminer.US

Type47
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Re: Burping the Rotax

Postby Type47 » Sun Sep 01, 2019 9:00 pm

Paul_G wrote:My procedure to check the oil level includes checking it when I finish a flight. When I arrive for another flight in a day or two, is it necessary to burp the Rotax and check it again? If there is no oil leaking, it should be good to go, correct? I'm wondering if it is necessary or can I just crank it up and go? What do you think?

Thanks in advance for your input.


If I understand it correctly, as the engine cools, a mild negative pressure is created in the engine case. This sucks a portion of the oil from the oil reservoir into the case.
Burping the engine by turning the engine through ( or holding it at) one or more piston compression strokes allows blowby to creat a mild pressure in the case causing the oil to be pushed back to the reservoir tank.
The only thing that would worry me about not burping would be if the oil level is high enough in the engine for the internal rotating parts to hit the oil and create foaming that is sucked into the system and introduce air bubbles into the lifters, a known weakness with the Rotax.
But I could be wrong.
Type47
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drseti
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Re: Burping the Rotax

Postby drseti » Sun Sep 01, 2019 9:06 pm

But if the oil tank had 3 litres of oil in it in the first place, and the oil is on the dipstick flat, there can't possible be too much oil in the crankcase.
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof H Paul Shuch
PhD CFII DPE LSRM-A/GL/WS/PPC iRMT
AvSport LLC, KLHV
fly@AvSport.org
AvSport.org
facebook.com/SportFlying
SportPilotExaminer.US

Type47
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Re: Burping the Rotax

Postby Type47 » Sun Sep 01, 2019 9:29 pm

drseti wrote:But if the oil tank had 3 litres of oil in it in the first place, and the oil is on the dipstick flat, there can't possible be too much oil in the crankcase.


Sure sounds right.
I can’t help but suspect that in a few years we will all be feeling silly about all the times we burped our engines when Rotax finally admits that it is unnecessary.
Type47
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I’m not a singing grampa.

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Re: Burping the Rotax

Postby drseti » Sun Sep 01, 2019 9:37 pm

On the contrary. It's great exercise, no matter what Rotax says. And besides, when people with wet sump engines ask me what the hell I'm doing, I get to reply "just winding up the rubber band"!
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof H Paul Shuch
PhD CFII DPE LSRM-A/GL/WS/PPC iRMT
AvSport LLC, KLHV
fly@AvSport.org
AvSport.org
facebook.com/SportFlying
SportPilotExaminer.US

3Dreaming
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Re: Burping the Rotax

Postby 3Dreaming » Sun Sep 01, 2019 10:09 pm

Type47 wrote:
Paul_G wrote:My procedure to check the oil level includes checking it when I finish a flight. When I arrive for another flight in a day or two, is it necessary to burp the Rotax and check it again? If there is no oil leaking, it should be good to go, correct? I'm wondering if it is necessary or can I just crank it up and go? What do you think?

Thanks in advance for your input.


If I understand it correctly, as the engine cools, a mild negative pressure is created in the engine case. This sucks a portion of the oil from the oil reservoir into the case.
Burping the engine by turning the engine through ( or holding it at) one or more piston compression strokes allows blowby to creat a mild pressure in the case causing the oil to be pushed back to the reservoir tank.
The only thing that would worry me about not burping would be if the oil level is high enough in the engine for the internal rotating parts to hit the oil and create foaming that is sucked into the system and introduce air bubbles into the lifters, a known weakness with the Rotax.
But I could be wrong.


The crankcase can not draw oil from the tank, because the line to the bottom of the crankcase from the tank is not below the oil level in the tank. There have been some installations with a high mounted oil tank with certain oil filters with flow back valves that didn't work like they should that had issues with oil from the tank flowing into the engine. Mostly what you get when burping the engine is the oil that was coating the inside of the engine that has drained to the lowest part of the crankcase.

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Re: Burping the Rotax

Postby FastEddieB » Mon Sep 02, 2019 6:27 am

I always check oil level after a flight.

Early on, I found that even having just run, I could not get consistent readings without burping.

On a historical note, back in 2007 Aeroshell had not yet introduced its Sport4 oil, so most of us ran on motorcycle oil. I forget the brand (Pennzoil?), but one that I used was known for “foaming”, which allegedly aggravated the inconsistency in readings.

In any case now, if I check right after a flight without burping, no oil may show on the flats. After burping it may then show 3/4 of the way up the flats. Due to that difference, my concern is that if I added oil based on the “before” reading, the “after” reading might actually indicate the engine had been overfilled.

Anyway, that’s my story and I’m sticking to it.
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drseti
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Re: Burping the Rotax

Postby drseti » Mon Sep 02, 2019 8:25 am

A few years ago, I had a customer who bought a Rotax powered LSA in CA, and flew it back to PA. He wanted routine service after the trip home. When I removed the oil tank cap, it gushed oil all over my hangar floor. Seems that, coming across the continent, every time he stopped for fuel, a line boy would check the dipstick, find it dry, and add a quart (!) of oil. Nobody taught him (or the line boys) about burping.
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof H Paul Shuch
PhD CFII DPE LSRM-A/GL/WS/PPC iRMT
AvSport LLC, KLHV
fly@AvSport.org
AvSport.org
facebook.com/SportFlying
SportPilotExaminer.US

3Dreaming
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Re: Burping the Rotax

Postby 3Dreaming » Mon Sep 02, 2019 11:41 am

3Dreaming wrote:
Type47 wrote:
Paul_G wrote:My procedure to check the oil level includes checking it when I finish a flight. When I arrive for another flight in a day or two, is it necessary to burp the Rotax and check it again? If there is no oil leaking, it should be good to go, correct? I'm wondering if it is necessary or can I just crank it up and go? What do you think?

Thanks in advance for your input.


If I understand it correctly, as the engine cools, a mild negative pressure is created in the engine case. This sucks a portion of the oil from the oil reservoir into the case.
Burping the engine by turning the engine through ( or holding it at) one or more piston compression strokes allows blowby to creat a mild pressure in the case causing the oil to be pushed back to the reservoir tank.
The only thing that would worry me about not burping would be if the oil level is high enough in the engine for the internal rotating parts to hit the oil and create foaming that is sucked into the system and introduce air bubbles into the lifters, a known weakness with the Rotax.
But I could be wrong.


The crankcase can not draw oil from the tank, because the line to the bottom of the crankcase from the tank is not below the oil level in the tank. There have been some installations with a high mounted oil tank with certain oil filters with flow back valves that didn't work like they should that had issues with oil from the tank flowing into the engine. Mostly what you get when burping the engine is the oil that was coating the inside of the engine that has drained to the lowest part of the crankcase.


In addition there should be no negative pressure in the crankcase after shut down. The positive pressure that is there when running will equalize to static pressure after shut down. There will always be a couple valves open in the engine. The same way the rings allow blow by to pressurize the crankcase, they will allow it to equalize through those open valves.

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Re: Burping the Rotax

Postby ShawnM » Mon Sep 02, 2019 5:08 pm

I was taught to burp the engine before the first flight of the day and I've been doing it this way for 6 years with zero issues on my SportCruiser. I dont burp it again on subsequent flights that day or at the end of the day. I dont burp it again until my first flight on another day when the cowl comes off for my preflight. After it burps if you give it another pull or two it'll burp a little more also.

My oil levels are always in the flat and I never have to add any oil during the year between my annual condition inspections.

I'm interested in checking it hot after my last flight of the day and then comparing that reading to my next burp during my preflight. Curious if there is a difference of not.

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Re: Burping the Rotax

Postby drseti » Mon Sep 02, 2019 5:23 pm

ShawnM wrote:I'm interested in checking it hot after my last flight of the day and then comparing that reading to my next burp during my preflight. Curious if there is a difference of not.


Oh, there's definitely a difference. Oil expands when hot, so the post-flight reading will be higher on the dipstick that the cold engine reading.
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof H Paul Shuch
PhD CFII DPE LSRM-A/GL/WS/PPC iRMT
AvSport LLC, KLHV
fly@AvSport.org
AvSport.org
facebook.com/SportFlying
SportPilotExaminer.US

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Warmi
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Re: Burping the Rotax

Postby Warmi » Mon Sep 02, 2019 5:34 pm

ShawnM wrote:I was taught to burp the engine before the first flight of the day and I've been doing it this way for 6 years with zero issues on my SportCruiser. I dont burp it again on subsequent flights that day or at the end of the day. I dont burp it again until my first flight on another day when the cowl comes off for my preflight. After it burps if you give it another pull or two it'll burp a little more also.

My oil levels are always in the flat and I never have to add any oil during the year between my annual condition inspections.

I'm interested in checking it hot after my last flight of the day and then comparing that reading to my next burp during my preflight. Curious if there is a difference of not.



How many blades on average it takes for your cold engine to burp ? Now that SlingPilot mentioned that his planes burps after 5-6 blades I am wondering if my average 30 blades is normal ..even though it has been like that since , well since forever ( in my case that’s 2017 )

Btw... it doesn’t matter how slow I turn - it seems to be more of function of how warm it is out there and how long since the last time the plane was flown ...
Flying Sting S4 ( N184WA ) out of Illinois


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