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JonathanMilbank
Joined: 14 Apr 2012
Posts: 390
Location: Aberdeen area
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 Posted: Fri Aug 16, 2024 5:20 am Post subject: Rotax 912ULS oil consumption |
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Does your 912ULS really use only 1/2 litre (500 ml), or 1/2 US quart of oil per 50 flying hours? Mine has done a total of 780 hours ( 560 since a rebuild at 220 hours, following a crash involving a previous owner ) and the oil consumption has steadily increased.
Every 50 hours I replace the oil filter with the Rotax supplied type and the oil is the recommended Aeroshell SPORT Plus 4. The instantaneous compression test done recently gives about 3% difference, highest 177psi to lowest 172psi, and aircraft climb performance remains strong at each annual permit renewal flight test. I won't do the scary leak-down compression test again, having once nearly broken my hand when the propeller kicked.
Researching on line tells me that the maximum acceptable consumption is 60 ml per flying hour, or 3 litres (3 US quarts) for 50 flying hours, while mine currently averages 40 ml / hour, or 2 litres / 50 hours. It grieves me when others tell that they hardly ever top up their oil tanks.
Oil pressure in flight is just over 4 bar or 60 psi. Oil temperature in the cruise varies seasonally between 80 and 100 deg C ( 176 and 212 deg F ). Living this far north means that most of the year it's at the cooler end.
The inside of the exhaust outlet tube is no more sooty than other people's engines with lower oil consumption. There's no "wet" oiliness evident in the exhaust, but a slight brown exhaust stain extends rearwards under the port wing and along the fuselage.
Last year the four inlet valve stem seals were replaced, but that didn't help either. Also when I borrowed a "cheap" not very clear boroscope, I couldn't see signs of scratching on the cylinder walls.
I'm starting to suspect that a few Rotax 912ULS owners may be deceiving themselves, although those I know locally definitely aren't.
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Area-51
Joined: 03 May 2021
Posts: 395
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| Posted: Sat Aug 17, 2024 1:27 am Post subject: Re: Rotax 912ULS oil consumption |
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181 has a 912UL with 1500hrs on it; top end overhauled 160hrs ago. It consistently uses 100ml every 5hrs, and I am not concerned about the consumption at all using Shell Sport+.
Some on other Rotax forums have mentioned using AGIP and other high performance motor cycle oils with better results, i.e reduction in oil consumption. However its unknown if these oils are formulated to retain their performance above 4500' altitudes.
If a 912UL/S is not burning oil then it is possible the fuel pump membrane is leaking fuel into the lubrication system. The result is thinning engine oil snd diminishing of lubrication performance. There was an AD on this issue.
On the preflight rollover burping an engine that takes longer to burp than another would indicate better sealing of the compression rings. A fast burp is not a good thing, it could be a symptom of worn compression rings. So rolling the prop over slower will burp the engine faster than rolling it over in a hurry.
Always check for oil leaks at the common spots and fix them if possible; crankcase parting line, valve pushrod tubes, valve rocker covers, oil return banjo at crankcase, oil pump case cover.
Hope this info helps.
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JonathanMilbank
Joined: 14 Apr 2012
Posts: 390
Location: Aberdeen area
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| Posted: Sun Aug 18, 2024 11:43 am Post subject: Re: Rotax 912ULS oil consumption |
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Thanks for the reply and suggestions. Apart from a slight weep from one valve cover, say about 6 drips per hour, which nothing I've tried to date can stem, there's no evidence of even the slightest leaks from the other locations which you mention.
Your explanation about burping / gurgling is a new one on me. I've always done it slowly and steadily and if done after a week or so since last flying, but forgetting to check oil level, it takes about 15 compressions to get the desired result. So I guess that means quite well sealing compression rings.
I've long since learned that to get a fairly accurate oil level reading from my engine, burp / gurgle IMMEDIATELY after the last flight of the day, then wait until the next day to look at the dipstick. Works for me!
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Area-51
Joined: 03 May 2021
Posts: 395
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| Posted: Sun Aug 18, 2024 2:37 pm Post subject: Re: Rotax 912ULS oil consumption |
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Sounds normal.
Doing the burping first then coming back to check level after the DI is completed seems to work well for oil level checking.
After resealing more than a few early style 912 valve covers I am convinced they suffer from porosity.
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h&jeuropa
Joined: 07 Nov 2006
Posts: 645
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| Posted: Tue Aug 20, 2024 6:03 pm Post subject: Re: Rotax 912ULS oil consumption |
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I have a different view on the oil check burping.
According to the Rotax Operators Manual,
1. Remove bayonet cap from the oil tank, turn the propeller
slowly by hand in direction of engine rotation several
times to pump residual oil from the engine into the oil
tank.
2 It is essential to build up compression in the combustion
chamber. Maintain the pressure for a few seconds to let
the gas flow via the piston rings into the crankcase. The
speed of rotation is not important but rather the continuous
pressure and the amount of gas which is transferred
into the crankcase.
3 This process is finished when air is returning back to the
oil tank and can be noticed by an audible gurgle from
the open oil tank.
4 Check oil level and add oil if necessary.
My understanding is that over time oil siphons from the tank back to the crankcase after the engine is shut down. "Burping" the engine uses compression to force the oil in the crankcase back into the tank.
We operated our 914 for nearly 1300 hours until the compression in several cylinders got low enough that the engine no longer performed well. They were around 60/80 psi with a differential test and 85 psi with a conventional test.
For the last several years we were unable to get the engine to burp prior to start, even rotating it 50 or 60 revolutions! We quit trying and instead when shutting down the engine, we checked the oil immediately since the tank was full and the siphoning had not yet started.
Our new 914 burps after just a few turns and the compression is much higher, it's difficult to rotate.
Notice that Rotax says to rotate slowly and to maintain the pressure to let the gas flow. That's exactly how we do it. You can feel the pressure drop and hear the air flowing.
I'm surprised that burping after the last flight of the day and then checking the oil level the next day gives a satisfactory result. I'd think the oil would siphon back to the sump during that time.
Just my thoughts and experience.
Jim Butcher
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Burrilla
Joined: 25 Apr 2015
Posts: 185
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| Posted: Tue Aug 20, 2024 10:25 pm Post subject: Rotax 912ULS oil consumption |
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I burp exactly as described after the last flight of day.
There is no siphon back even over several days between flight.
I think there is an air gap in the return to the tank, otherwise you wouldn’t hear the burp, that prevents siphoning.
Alan
Sent from my iPad
| Quote: | On 21 Aug 2024, at 03:05, h&jeuropa <butcher43(at)att.net> wrote:

I have a different view on the oil check burping.
According to the Rotax Operators Manual,
1. Remove bayonet cap from the oil tank, turn the propeller
slowly by hand in direction of engine rotation several
times to pump residual oil from the engine into the oil
tank.
2 It is essential to build up compression in the combustion
chamber. Maintain the pressure for a few seconds to let
the gas flow via the piston rings into the crankcase. The
speed of rotation is not important but rather the continuous
pressure and the amount of gas which is transferred
into the crankcase.
3 This process is finished when air is returning back to the
oil tank and can be noticed by an audible gurgle from
the open oil tank.
4 Check oil level and add oil if necessary.
My understanding is that over time oil siphons from the tank back to the crankcase after the engine is shut down. "Burping" the engine uses compression to force the oil in the crankcase back into the tank.
We operated our 914 for nearly 1300 hours until the compression in several cylinders got low enough that the engine no longer performed well. They were around 60/80 psi with a differential test and 85 psi with a conventional test.
For the last several years we were unable to get the engine to burp prior to start, even rotating it 50 or 60 revolutions! We quit trying and instead when shutting down the engine, we checked the oil immediately since the tank was full and the siphoning had not yet started.
Our new 914 burps after just a few turns and the compression is much higher, it's difficult to rotate.
Notice that Rotax says to rotate slowly and to maintain the pressure to let the gas flow. That's exactly how we do it. You can feel the pressure drop and hear the air flowing.
I'm surprised that burping after the last flight of the day and then checking the oil level the next day gives a satisfactory result. I'd think the oil would siphon back to the sump during that time.
Just my thoughts and experience.
Jim Butcher
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=513795#513795
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budyerly@msn.com
Joined: 05 Oct 2019
Posts: 287
Location: Florida USA
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| Posted: Wed Aug 21, 2024 11:52 am Post subject: Rotax 912ULS oil consumption |
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Apparently, my photos were too large. OOPS! Here is a reprint of my email from this morning minus photos that are in the word attachment.
Bud Yerly
From: Bud Yerly <budyerly(at)msn.com>
Sent: Wednesday, August 21, 2024 9:46 AM
To: europa-list(at)matronics.com <europa-list(at)matronics.com>
Subject: Re: Re: Rotax 912ULS oil consumption
I agree with Jim and have written on this in my techniques paper on Rotax Troubleshooting.
I was emailing back and forth with Ron Paragoris, who is nearing engine run and finding that drip, drip, drip, out of the turbo.
Oil in the 914 will always slowly drain from the oil pump, into the return line of the turbo (which has no check valve) and after a few weeks to a month fill the turbo can, inlet, air filter, muffler, etc. with a small but annoying amount of oil.
If your Rotax drops below about 76/80 on a differential compression check get a top overhaul accomplished. It mainly will need the valves cleaned up. I do a full gearbox rebuild between 500 and 600 hours. Why not pull the cylinders and clean up the heads at the same time. My 500-hour engine now is at nearly 80/80 and the compression on my 914 feels like a 912S. It burps in only ½ the number of blades. I burp a second time from habit, and my oil level is about ¾ to half way up the new dip stick which is normal for my particular engine and tank height.
I don't normally re-burp after a flight to check the oil level unless I am just checking my fill level on cross country. My old 914 has always pushed out about ¼ of a pint (0.25L) after about 10 hours. Then it pretty much stays there. by the 20-30 hours of my annual flying I see only a ½ liter lost per oil change.
The oil mess of the 914 is through the turbo. I rarely see much oil coming out of my oil tank vent tube. I installed a drip can on my oil vent and have monitored the oil out of my vent tube and it amounts to about 2 oz. in about 20 hours (yea that's all I fly per year now). The 912 and 912S in my opinion are free of turbo drips. So, the only loss should be through the rings, valves and the oil vent line. Do not underestimate the amount of suction on the oil vent line issue. The vent should be done IAW the Rotax installation manual to prevent continuous suction out the vent line. The vapor contains water and oil, and you will note oil on the belly coming out of the vent if it is sucking oil out. Plus an improperly made oil vent line may lower the ability of the engine to return oil to the tank.
I'm including some of what Ron and I discussed and a paper on my oil drip cans. (Drip cans can be more of a pain than they are worth.)
Questions have ** and the answers follow:
** If the engine isn't turned over since I removed 3/4oz of oil from the turbo, will it refill and leak out through the air cleaner again?
It has been my experience that yes it will drip down into your can under the turbo mostly through the oil return line! Most of us make or made sure the feed check ball valve to the turbo is clean and operating but there isn't anything we can do about the oil seeping out between the pump gears back into the oil drain line from the turbo which is the lowest point of the engine. The oil seep is about 5-15cc per week in my experience. This dripping through the oil pump fills the cold turbo seal, and runs out the turbo inlet and exhaust side. The oil fills the air filter but frankly is harmless and eventually makes a mess of your cowl.
On start up, if the oil is not sucked out after setting a month, will be flung up into the plenum and get burned in the cylinders. I don't normally see a problem with this to the carb performance but the plugs do sometimes get oil soaked. Especially if the plugs are old or if were mechanically cleaned. Plugs need a good sharp point to form the jump between the electrode and ground bar. The edges on the older plug tend to round out. The good news is it affects the lower plugs more than the upper so starts are normally not seriously affected in the 914.
On startup, the oil in the exhaust will cover the left gear, wing root and belly. Messy, but harmless.
** When flying, can you start the motor with oil filling the turbo and leaking out the air cleaner?
When flying you will have no issue with restarting.
** If your answer is that it's not a good idea to start with oil leaking out the air cleaner, do you recommend cleaning the air cleaner? How to clean it?: Real clean job of using air cleaner cleaning solution and then oil with air cleaner oil? Or perhaps wrap with paper towels and blot out most of the excess oil?
If the plane has sat for a few weeks or a month, I tend just start it up. Some oil gets spattered out of the exhaust, and the lower plugs will get oil soaked. I run the engine up after run up and burn off the oil from the plugs. It is not uncommon to see a 500 RPM mag drop, from oil soaked plugs so simply running it up to max continuous power for a minute disturbs the neighbors but cleans the plugs off enough to get about a 300 RPM drop.
** After a flight, on a normal 914 that has a pretty good sealing turbo oil check valve, how long sitting will usually have oil coming out of the air cleaner?
I think that was answered above.
** Have you devised a way of draining oil from the turbo without having to remove the cowl?
I have made an experimental oil catch for my air filter. It prevents some of the oil from soaking the oil filter paper. I think most use K&N filters but a cheap Fram may be as good and just throw it away. I use the 20 degree bend filter and just clean it with every other oil change and or annually because I don't fly that much any longer.
What a pain to make and ensure that it won't get sucked into the turbo. It is just a plate that contacts the lip of the turbo inlet then has a depression for the oil to settle in. It works OK so far. Oil does drain down and out through a tube. If the oil puddle builds up under the engine, then it is probably prudent to suck the oil out of the turbo. Or just start up, run the engine, then go to the wash rack and wash off the oil spatter on the aircraft belly, gear and wing. Good news for the mono is the brake is on the opposite side of the tire from the exhaust.
For the 912/912S guys you can see this turbo issue is not an issue you must contend with. However, you have another issue that water can enter your air filter plenum and fill your manifold, float bowls and engine cylinders if the plane is setting outside in the rain. Any valve that is open in the cylinder will allow water to enter the cylinder. It will create mold in your plenum bottom and make a mess. This is very true of the trigear. Keep your drain holes clear, and I written on how I avoid the rain getting in through the inlet. It will save engine internal corrosion and many problems. Keep your pretty airplane in a hangar or purchase a cockpit and engine cover if you must have an outside tie down.
If your 912 is using oil, consider a top overhaul on your 912 and check your lifters. Clean up the valves (lapping) check the rings and your lifters. If they are fine, don't fool with them. Watch your vent line draft. That renewal of your valve seats can be a game changer. It doesn't matter if you use unleaded, ethanol laced or 100LL fuel, valves get dirty and compression and power will suffer.
Best Regards to all,
Bud Yerly
Custom Flight Creations, Inc.
From: owner-europa-list-server(at)matronics.com <owner-europa-list-server(at)matronics.com> on behalf of h&jeuropa <butcher43(at)att.net>
Sent: Tuesday, August 20, 2024 10:03 PM
To: europa-list(at)matronics.com <europa-list(at)matronics.com>
Subject: Re: Rotax 912ULS oil consumption
--> Europa-List message posted by: "h&jeuropa" <butcher43(at)att.net>
I have a different view on the oil check burping.
According to the Rotax Operators Manual,
1. Remove bayonet cap from the oil tank, turn the propeller
slowly by hand in direction of engine rotation several
times to pump residual oil from the engine into the oil
tank.
2 It is essential to build up compression in the combustion
chamber. Maintain the pressure for a few seconds to let
the gas flow via the piston rings into the crankcase. The
speed of rotation is not important but rather the continuous
pressure and the amount of gas which is transferred
into the crankcase.
3 This process is finished when air is returning back to the
oil tank and can be noticed by an audible gurgle from
the open oil tank.
4 Check oil level and add oil if necessary.
My understanding is that over time oil siphons from the tank back to the crankcase after the engine is shut down. "Burping" the engine uses compression to force the oil in the crankcase back into the tank.
We operated our 914 for nearly 1300 hours until the compression in several cylinders got low enough that the engine no longer performed well. They were around 60/80 psi with a differential test and 85 psi with a conventional test.
For the last several years we were unable to get the engine to burp prior to start, even rotating it 50 or 60 revolutions! We quit trying and instead when shutting down the engine, we checked the oil immediately since the tank was full and the siphoning had not yet started.
Our new 914 burps after just a few turns and the compression is much higher, it's difficult to rotate.
Notice that Rotax says to rotate slowly and to maintain the pressure to let the gas flow. That's exactly how we do it. You can feel the pressure drop and hear the air flowing.
I'm surprised that burping after the last flight of the day and then checking the oil level the next day gives a satisfactory result. I'd think the oil would siphon back to the sump during that time.
Just my thoughts and experience.
Jim Butcher
Read this topic online here:
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