Rotax 912 ULS Engine Oil Level

[skippydiesel]

Just thought I would share this cold weather observation with all the Rotax 912 drivers -

 

I always "burp"/ "gurgle" my engine before first start up of the day. Then check my oil level.

 

Usually there is very little change in the oil level between service hours.

 

Last 2-3 pre start "burps" (over night temps down to near or below 0 degrees) the oil has only come up to the halfway mark.

 

Today I decided to add oil (I like it to be near the full mark).

 

Went to fetch oil. Came back. Dont know why, but checked level again - FULL!!

 

Thought about this and postulate - cold oil = thick gluggy oil (slow). Oil still moving slowly through system when I have checked the level.

 

I could have easily overfilled and blown excess oil overboard - waste & mess.

 

In future, during cold weather, will wait a few minutes to check level - I suggest you do the same.

 

 

[Super Cub]

Never operated one in that lower Ground temp.

 

But good to know.

 

Noted Thanks

 

 

[Blueadventures]

Just thought I would share this cold weather observation with all the Rotax 912 drivers -I always "burp"/ "gurgle" my engine before first start up of the day. Then check my oil level.

 

Usually there is very little change in the oil level between service hours.

 

Last 2-3 pre start "burps" (over night temps down to near or below 0 degrees) the oil has only come up to the halfway mark.

 

Today I decided to add oil (I like it to be near the full mark).

 

Went to fetch oil. Came back. Dont know why, but checked level again - FULL!!

 

Thought about this and postulate - cold oil = thick gluggy oil (slow). Oil still moving slowly through system when I have checked the level.

 

I could have easily overfilled and blown excess oil overboard - waste & mess.

 

In future, during cold weather, will wait a few minutes to check level - I suggest you do the same.

Hi Skippy I read and copied this bit of info as I was curious for the same reasons. "It is also normal to see a slightly lower amount of oil on a cold engine versus an engine that has just been running. This is primarily due to the high viscosity oil sticking to internal engine parts. " Seems to be a valid explanation. Colder probably holds a bit more oil on the parts. Cheers

 

 

[facthunter]

If the return line was made with a large diameter it won't return oil that thins right out when hot. Why? A big slug of air will get through the mass of the oil and the oil doesn't go up the pipe reliably. It tends to run back, so

 

The smaller pipe will not allow the air to pass through the column of oil but the thick oil will move slowly through the pipe. In these circumstances I would consider running the engine at idle revs for a while then rechecking the level after shutting down the engine. The oil will have warmed up enough to thin out a bit and should burp normally. Straws are always thin for a reason. Nev

 

 

[skippydiesel]

Hi Nev,

 

All the oil lines on my 912 are standard - as supplied by B Flood. At this stage - no plans to change.

 

I don't usually have a problem getting a satisfactory preflight oil tank fill, to check the oil level but just happen to have done a few early (cold) morning ops lately. Unusual for me as I have a strong aversion to the winter cold and don't usually venture out much before mid morning/lunch time. I think this is how the slow filling of the oil tank/reservoir had not come to my notice befor.

 

Strangely I have not heard/read of this phenomena before either, that's why I thought it worth bringing to everyone's attention.

 

The oil level checking instructions should read -

 

Chock wheels/brake on

 

Ensure ignition off

 

Remove oil tank/reservoir cap.

 

Rotate engine slowly clockwise (keeping body/limbs clear of prop arc) until burp/gurgle heard.

 

WAIT

 

a minute or two to allow oil level to settle.

 

Check oil level - add oil if necessary

 

Replace cap

 

Its hardly an important issue but may save others from wasting oil and messing up their aircrafts belly.

 

 

[facthunter]

The oil pipe fitted by the maker is what generally works. I'm not suggesting modifying it. The "silly" return system . ( it IS pretty unusual) relies on Leakage past the piston rings. (turn the motor slowly works best, and new motors don't leak much so turn them even slower). The crankcase gets pressurised and forces the oil up the pipe till it's all gone and the air then burps/gurgles. I think residual case pressurisation forced more oil up into your oil tank, after you stopped turning the motor. Most oils recommended are synthetic aren't they? They should be thinner at low temps that mono grade mineral oils.. Nev

 

 

[skippydiesel]

I agree it's a very different (from all other multi cylinder engines) oil circulation systems but it seems to work well, albeit at disconcertingly low pressur.

 

Yes - I worked out long ago that the slower you turn the quicker it seems to get to the "gurgle".

 

I use the Rotax recommended AeroShell Sport Plus 4 - it is described by Shell as a "Multigrade oil designed to be used in any climate, anywhere in the world" &

 

"Specially selected base oils incorporating synthetic technology ".

 

One web page described it as a 10W-40 but most do not give or even hint at a viscosity index.

 

As a multi grade it will certainly be thinner (than mono grades) when cold (that is when not at full engine operating temp). I don t believe this means that it gets thinner the colder it gets - only that it has lower viscosity at engine start up. If you need thinner at the cold end, you would need to look at something like a 5W-40 or a 0W-30 (not suggesting you or anyone else, is actually seeking thinner oil and as far as I know not recommended for 912's)

 

 

[Blueadventures]

I agree it's a very different (from all other multi cylinder engines) oil circulation systems but it seems to work well, albeit at disconcertingly low pressur.Yes - I worked out long ago that the slower you turn the quicker it seems to get to the "gurgle".

 

I use the Rotax recommended AeroShell Sport Plus 4 - it is described by Shell as a "Multigrade oil designed to be used in any climate, anywhere in the world" &

 

"Specially selected base oils incorporating synthetic technology ".

 

One web page described it as a 10W-40 but most do not give or even hint at a viscosity index.

 

As a multi grade it will certainly be thinner (than mono grades) when cold (that is when not at full engine operating temp). I don t believe this means that it gets thinner the colder it gets - only that it has lower viscosity at engine start up. If you need thinner at the cold end, you would need to look at something like a 5W-40 or a 0W-30 (not suggesting you or anyone else, is actually seeking thinner oil and as far as I know not recommended for 912's)

The first number in the oil weight relates to cold flow and the second number relates to viscosity when hot. Cheers

 

 

[facthunter]

in Alaska Russia and Canada they use external heat to keep the engines from having an oil thickening problem at low ambients . Some radials operated in very cold climates diluted the engine oil on shutdown with fuel which then evaporated on warm up or you couldn't turn the motors over. Transmission oils are diluted with kerosene. You do what you have to in extreme conditions. Nev

 

 

[aripilot]

Sport Aviation July 2017 issue has excellent article about burping Rotax.

 

 

[Ayecapt]

Just thought I would share this cold weather observation with all the Rotax 912 drivers -I always "burp"/ "gurgle" my engine before first start up of the day. Then check my oil level.

 

Usually there is very little change in the oil level between service hours.

 

Last 2-3 pre start "burps" (over night temps down to near or below 0 degrees) the oil has only come up to the halfway mark.

 

Today I decided to add oil (I like it to be near the full mark).

 

Went to fetch oil. Came back. Dont know why, but checked level again - FULL!!

 

Thought about this and postulate - cold oil = thick gluggy oil (slow). Oil still moving slowly through system when I have checked the level.

 

I could have easily overfilled and blown excess oil overboard - waste & mess.

 

In future, during cold weather, will wait a few minutes to check level - I suggest you do the same.

Where should you stand whilst burping your Rotax? In terms of safest position.

 

 

[old pilot]

Never operated one in that lower Ground temp.But good to know.

 

Noted Thanks

I agree it's a very different (from all other multi cylinder engines) oil circulation systems but it seems to work well, albeit at disconcertingly low pressur.Yes - I worked out long ago that the slower you turn the quicker it seems to get to the "gurgle".

 

I use the Rotax recommended AeroShell Sport Plus 4 - it is described by Shell as a "Multigrade oil designed to be used in any climate, anywhere in the world" &

 

"Specially selected base oils incorporating synthetic technology ".

 

One web page described it as a 10W-40 but most do not give or even hint at a viscosity index.

 

As a multi grade it will certainly be thinner (than mono grades) when cold (that is when not at full engine operating temp). I don t believe this means that it gets thinner the colder it gets - only that it has lower viscosity at engine start up. If you need thinner at the cold end, you would need to look at something like a 5W-40 or a 0W-30 (not suggesting you or anyone else, is actually seeking thinner oil and as far as I know not recommended for 912's)

[old pilot]

Hi skippy diesel

 

I operate a 912 ul in my Tecnam at 3840 ft elv at @minus 7 and minus 9 as yet have not had a problem with oil levels I run the aero shell sport plus 4 ,the oil is up to change time I might just be lucky thanks anyway

 

 

[Ayecapt]

Just thought I would share this cold weather observation with all the Rotax 912 drivers -I always "burp"/ "gurgle" my engine before first start up of the day. Then check my oil level.

 

Usually there is very little change in the oil level between service hours.

 

Last 2-3 pre start "burps" (over night temps down to near or below 0 degrees) the oil has only come up to the halfway mark.

 

Today I decided to add oil (I like it to be near the full mark).

 

Went to fetch oil. Came back. Dont know why, but checked level again - FULL!!

 

Thought about this and postulate - cold oil = thick gluggy oil (slow). Oil still moving slowly through system when I have checked the level.

 

I could have easily overfilled and blown excess oil overboard - waste & mess.

 

In future, during cold weather, will wait a few minutes to check level - I suggest you do the same.

My instructor taught me that one gurgle is never enough , to get a true oil level takes more than one burst of air through the reservoir . This might be even more important in cold conditions. .?

 

 

[old pilot]

I'm sure that is correct I always burp mine twice winter or summer

 

 

[facthunter]

The air only gets there when the oil is nearly all gone so I reckon any decent gurgle is good enough indicator. It's only so as you don't overfill the engine by having the engine with a lot of oil still in it when you top up the tank.

 

A good engine has to be turned quite slowly to allow the gas past the piston rings. You hold the prop with both hands to stop it turning under the effect of the compression that hasn't yet escaped in that situation. I don't like moving ANY prop by hand standing in the prop arc but done where you allow all of the gas to escape is safest of all techniques and most effective at getting the oil to return. It's not the number of turns you make. It's the volume of gas that gets in the crankcase You could achieve the same with a bicycle tyre pump of the was a place to put it.. It's a pretty silly system, I feel. Most engine designs try to reduce crankcase pressure to zero or even less as it reduces oil leaks .Nev

 

 

[Guest Hampden]

Just thought I would share this cold weather observation with all the Rotax 912 drivers -I always "burp"/ "gurgle" my engine before first start up of the day. Then check my oil level.

 

Usually there is very little change in the oil level between service hours.

 

Last 2-3 pre start "burps" (over night temps down to near or below 0 degrees) the oil has only come up to the halfway mark.

 

Today I decided to add oil (I like it to be near the full mark).

 

Went to fetch oil. Came back. Dont know why, but checked level again - FULL!!

 

Thought about this and postulate - cold oil = thick gluggy oil (slow). Oil still moving slowly through system when I have checked the level.

 

I could have easily overfilled and blown excess oil overboard - waste & mess.

 

In future, during cold weather, will wait a few minutes to check level - I suggest you do the same.

Have you tried starting the engine, stopping and burping again, don't know why but it will probably give a higher reading!

 

 

[skippydiesel]

Have you tried starting the engine, stopping and burping again, don't know why but it will probably give a higher reading!

Friend Hampden - With a few exceptions, engine oil is checked when the engine is cold, with the aircraft standing on level ground.

 

My opening observation was just that, an observation that I thought might be of interest to other Rotax 912 drivers - I don't have a problem that needs solving. Nor do I wish to deviate from the Rotax advice to "burp" your engine befor start up.

 

The burping not only fills the engine oil tank so that its level can be checked, it also:

 

Clears any build up of oil that may have pooled inside a cylinder.

 

Pre lubricates all the internal moving parts.

 

Allows the pilot to make a rough check on compression.

 

May "charge" the pressure lubrication system, so that oil is being circulated from the moment of start up.

 

Added to the above is the, possibly perverse, pleasure I get from just going through this little ritual.

 

 

[Guest Hampden]

Friend Hampden - With a few exceptions, engine oil is checked when the engine is cold, with the aircraft standing on level ground.My opening observation was just that, an observation that I thought might be of interest to other Rotax 912 drivers - I don't have a problem that needs solving. Nor do I wish to deviate from the Rotax advice to "burp" your engine befor start up.

 

The burping not only fills the engine oil tank so that its level can be checked, it also:

 

Clears any build up of oil that may have pooled inside a cylinder.

 

Pre lubricates all the internal moving parts.

 

Allows the pilot to make a rough check on compression.

 

May "charge" the pressure lubrication system, so that oil is being circulated from the moment of start up.

 

Added to the above is the, possibly perverse, pleasure I get from just going through this little ritual.

I didn't say to warm it, just to run and recheck and I didn't say there was any logic to it! It has just been observed.

 

 

[peterg]

Sport Aviation July 2017 issue has excellent article about burping Rotax.

I couldn't see the article - what page is it on?

 

 

[skippydiesel]

Where should you stand whilst burping your Rotax? In terms of safest position.

Clear of the prop arc - always assume a prop/ignition is live.

 

 

[facthunter]

IF you grip the prop firmly and move it slowly the compression will leak away. It wont fire with any force at all if by chance it did, with most of the gases leaked away. It is possible to flick a Rotax and start it. It's been done quite a few times. The rotational speed has to be high and right at the point of firing which is quite a few degrees before TDC except where an impulse is fitted. (Most normal Aero engines) where it's delayed and is about TDC at minimal rotational speed. There is really no conceivable way a spark would occur with a Rotax 912 without a fairly rapid movement of the prop in reality but caution is a good approach in all matters.

 

With an impulse fitted you could just brush the prop if it had stopped in the perfect spot and it will fire the Magneto. Some engines after shutdown HOT can burst into life after periods like 5 minutes if loose flakey carbon is smouldering away inside. I've seen it happen on an Avro with Arnstrong Siddeley Genet Major radial engine . It was just parked there with no one around and burst into life. They were renowned for overheating without a "Townend Ring" fitted. Nev

 

 

[skippydiesel]

Thanks for that Nev - I guess my early training is showing. Sometimes the old habits just feel safe, even when they may be redundant. I know of Rotax 912 drivers who cant be bothered with "burping" and seem to get away with it . I get satisfaction from going through this sort of ritual, All part of my preflight checks. If I get interrupted, I get cranky and often have to start from scratch to feel that I have "done the job" properly.

 

 

[alf jessup]

I usually burp mine after the flight

 

I find the oil comes back in to the canister much easier

 

Also allows me to look over the hot engine for leaks with the cowls open

 

Another reason is I like the cowls open to not bake the ignition modules with the latent heat of a hot engine

 

 

[skippydiesel]

Hi Alf - Not sure that Rotax would agree with the post flight burp, but I am actually more interested in the heat soaked engine & the the baked ignition modules.

 

My aircraft does not facilitate the opening of engine cowl (multiple fixings must be removed) however I have long been concerned with the unnecessary containment of engine heat after shutdown. In my case the contained heat may be contributing to fuel vaporisation, making subsequent hot starts (failures) embarrassing. To mitigate this I open my oil/coolant inspection hatch to allow the heat to dissipate more readily. Seems to work, at least some of the time.

 

What makes you think the ignition modules are not designed to withstand the heat emanating from a hot engine?

 

Going back to the post flight burp - by checking your oil level outside the accepted regime, you may introducing variables that Rotax designers/engineers may have not allowed for. I am not an engineer but I do know that in land based engines, allowing the oil to flow back into the sump usually gives a better measure of oil quantity, than when the engine has been recently run. Hence the advise to check the oil level before the first start of the day or at least after a suitable cooling off/drain down period.