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oil tank vent - 2 questions

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hevansrv7a

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I am trying to "install" my engine dehydrator. I am using the "BlackMax" from Aircraft Components Inc. in Findlay OH and the owner is trying very hard to be helpful. I had the dryer beads model on my 7A but I am running into issues putting the same idea into practice on my new-to-me 12. The model of the dryer is not a factor because they both work the same way on the engine.

www.flyingsafer.com

The dryer pumps dehydrated air into the oil vent and thus into the rest of the engine. It worked fantastically well on the Lyco-clone but this is a Rotax. There are 2 tubes coming out the bottom of the engine compartment.

One tube is clear, flexible plastic or vinyl and the other is black rubber. the clear one has an ID slightly larger than the rubber one. The rubber one has, of course, larger OD. Both are much smaller than the vent on a conventional 360" engine.

Q1: which tube is the oil sump vent and what is the other one? I found the source at the top of the oil tank just below the filler cap but there is so much stuff in the engine compartment that it's not obvious what I want to know.

Q2: where is the hole in the oil vent tube that is often called the "ice hole"? the pressure from the dryer pump has to be upstream of that.

THANKS
 
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The 912 is a dry sump engine. There is no vent from the sump. Oil is forced into the tank directly from the sump..

http://www.lightaircraftassociation.../Rotax Service Interval Guide April 2011.pdf

https://en.wikipedia.org/wiki/Rotax_912

I don't think this is a correct understanding. There is a vent in the filler neck about .25 to .5" below the top of the neck which is visible when the filler cap is off.

There is another thread in the RV-12 forum on drips from that tube.
 
The oil tank does have a vent, yes. But, the sump itself cannot have a vent, or oil could not be pushed back into the tank. Please reference the diagrams and explanations in the documents linked below.
 
The 912 is a dry sump engine. There is no vent from the sump. Oil is forced into the tank directly from the sump..

http://www.lightaircraftassociation.../Rotax Service Interval Guide April 2011.pdf

https://en.wikipedia.org/wiki/Rotax_912

I don't think this is a correct understanding. There is a vent in the filler neck about .25 to .5" below the top of the neck which is visible when the filler cap is off.

There is another thread in the RV-12 forum on drips from that tube.

See item 7 on the page I included here.
 

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I think what is trying to be said is... Rotax 9-series engines have what is essentially a sealed crankcase. Oil in the reservoir tank hose prevents air ingress into the crankcase. As such, no moisture can enter the engine, and so not dehydration is necessary...
 
To say it in even simpler terms, you can’t install a dehydrator system on a Rotax 912 engine. There will be no airflow through the engine crank case itself. The only thing you will be dehydrating is the oil tank and I don’t see much benefit in that.
 
I think what is trying to be said is... Rotax 9-series engines have what is essentially a sealed crankcase. Oil in the reservoir tank hose prevents air ingress into the crankcase. As such, no moisture can enter the engine, and so not dehydration is necessary...

It is well established that the byproducts of the combustion of gasoline include lots of water in vapor form. The crankcase pressure is from that blowby gas. The hot gas can (thus) hold lots of moisture. The cooling gas must then release the water in the form of condensation. This is not dependent upon the kind of sump, etc.

The water vapor that matters doesn't enter from ambient air so much as from the combustion itself. I used to see beads of water on the dip stick on my O-200 in my C-150 - as an example.

Arguing about this is pointless and not what I was asking, anyhow.
 
The water vapor that matters doesn't enter from ambient air so much as from the combustion itself. I used to see beads of water on the dip stick on my O-200 in my C-150 - as an example.
Arguing about this is pointless and not what I was asking, anyhow.

Correct.... I had A65-8 in my Cub, and oil cap and dipstick had droplets of water more often than not. You will not see this phenomenon with Rotax 9-series engines...
 
There's a lot of LSA airplanes out there with Rotax 912 motors on them. The Rotax engine has aluminum pistons and bores. The heat of the engine oil is such that moisture, does not end up condensing anywhere in any areas such that a dehydrator is necessary.

If a dehydrator was necessary on a Rotax, the manufacturer would haved include it in the design, and Van's would have included it in the kit, which they didn't.

This isn't a Lycoming or a Conti.
 
It is well established that the byproducts of the combustion of gasoline include lots of water in vapor form. The crankcase pressure is from that blowby gas. The hot gas can (thus) hold lots of moisture. The cooling gas must then release the water in the form of condensation. This is not dependent upon the kind of sump, etc.

The water vapor that matters doesn't enter from ambient air so much as from the combustion itself. I used to see beads of water on the dip stick on my O-200 in my C-150 - as an example.

Arguing about this is pointless and not what I was asking, anyhow.

I don't think he or anyone else was arguing the against the science of water vapor accumulation within a combustion engine.

What has been explained, is that there is no way for you to connect a dehydrator to a Rotax 912 engine and have it dry the air within the engine.
The interior of the engine is only connected to the outside world via the oil lines that connect it to the oil tank.
Those oil lines are full of oil even when the engine is not running, so there is no way to flow low humidity / exchange air through the inside of the engine with a dehydrator system.
 
There's a lot of LSA airplanes out there with Rotax 912 motors on them. The Rotax engine has aluminum pistons and bores. The heat of the engine oil is such that moisture, does not end up condensing anywhere in any areas such that a dehydrator is necessary.

If a dehydrator was necessary on a Rotax, the manufacturer would haved include it in the design, and Van's would have included it in the kit, which they didn't.

This isn't a Lycoming or a Conti.

If Lycoming, Conti, etc. neglected to include it in their designs why would your logic necessarily be true for Rotax?

According to Lockwood, the cylinders are aluminum but the bores are ceramic. But what about the crank, rods, etc?

The answer from the Van's employee may be correct but I will be doing an experiment to verify it.

Your concept about the heat of the engine ignores the main point about how moisture gets inside any engine.

Yes, the clearances are very tight as compared to Lyco etc. but they are not zero and the blow by pressure is part of the design. The gases that do blow by contain the same proportion of moisture as would any gasoline Otto cycle engine.

So you are one more responder who says I should not be doing what I am doing instead of either letting it go or trying to answer the actual question. I suppose you also mean well, but all I wanted was simple answers from people with 12's who might already know about those vents.
 
Please go ahead but just know you are going to be drying the air on the inside of the oil tank and then only on the surfaces that are above the oil level. The dry air cannot physically get into the crankcase.
 
The answer from the Van's employee may be correct but I will be doing an experiment to verify it.

It is correct.
So I suggest you use caution so as not to use atmospheric pressure / vacuum to empty those lines in any way while you try and move air through the engine.
If you do so, at next engine start the engine will be starved for oil and damage will result.

This is why Rotax has very specific procedures for what to do when completing an oil change or after doing any maintenance that required breaking open the oil system in any way.
As an RV-12 owner, you should get familiar with those procedures, even if you do not do any experimenting.
 
H Evan, you are correct that water is a byproduct of combustion. If the engine is warmed up to the recommended temperature, then that water turns to steam and most of it will be vented out of the oil tank vent line. Very little water remains in the engine.
The clear tube in your RV-12 is the oil tank vent line. The rubber tube is most likely connected to the fuel pump.
Normally the fuel pump will not leak any liquids, but it could leak either lubricating oil or gasoline if a seal or diaphragm fails.
 
H Evan, you are correct that water is a byproduct of combustion. If the engine is warmed up to the recommended temperature, then that water turns to steam and most of it will be vented out of the oil tank vent line. Very little water remains in the engine.
The clear tube in your RV-12 is the oil tank vent line. The rubber tube is most likely connected to the fuel pump.
Normally the fuel pump will not leak any liquids, but it could leak either lubricating oil or gasoline if a seal or diaphragm fails.

THANK YOU.

btw, the maker of the dryer suggested a simple test. The way it is supposed to work is that dry air is pumped into the system through the oil vent and exits through the exhaust. He suggested taping a plastic bag over the exhaust and letting it run for a day. The bag will either inflate or it won't. If it does not he will take the device back. The trick is to get a good seal on the connection from the pump to the engine, upstream of the "ice hole".
 
It is correct.
So I suggest you use caution so as not to use atmospheric pressure / vacuum to empty those lines in any way while you try and move air through the engine.
If you do so, at next engine start the engine will be starved for oil and damage will result.

This is why Rotax has very specific procedures for what to do when completing an oil change or after doing any maintenance that required breaking open the oil system in any way.
As an RV-12 owner, you should get familiar with those procedures, even if you do not do any experimenting.

Thank you for your input. I appreciate your expertise, experience and good intentions. I am, like everyone else here, a huge Van's Aircraft fan. The experiment will not produce a problem as far as I can see. The pump can't make enough pressure to move oil through a line. I described it in in another post. I agree that every owner should be familiar with what the manufacturer says.

7-1183
 
Watch this video about purging the Rotax oil system.
https://www.youtube.com/watch?v=UwARvpIP9-k
The man mentions that the oil tank cap is not air tight.
So any air that is pumped into the oil tank will leak out of the cap.
Even if the cap did not leak air, no air can enter the engine through the oil hoses because both hoses are full of oil, or should be.
There is no hole in the oil vent tube, unless you count the ones at each end of the tube. One end of the tube connects to the oil tank and the other end is open at the bottom of the cowl.
I suppose that dry air could be pumped into the muffler exhaust pipe and it would come out of the air filters. Not that I am recommending doing that.
 
The design of the Rotax as everyone is describing doesn’t allow air into the engine. In fact if you do an oil change incorrectly and allow air into the system, you have to pressure purge the system. Failure to do this can cause catastrophic issues including engine damage requiring replacement. So the dryer filter doesn’t apply to the Rotax design.
 
Watch this video about purging the Rotax oil system.
https://www.youtube.com/watch?v=UwARvpIP9-k
The man mentions that the oil tank cap is not air tight.
So any air that is pumped into the oil tank will leak out of the cap.
Even if the cap did not leak air, no air can enter the engine through the oil hoses because both hoses are full of oil, or should be.
There is no hole in the oil vent tube, unless you count the ones at each end of the tube. One end of the tube connects to the oil tank and the other end is open at the bottom of the cowl.
I suppose that dry air could be pumped into the muffler exhaust pipe and it would come out of the air filters. Not that I am recommending doing that.
Your idea about putting dry air into the muffler is exactly what I proposed last night to the manufacturer. It could get to the crank and rods through the piston ring gaps. I have not heard from him yet.
 
I've heard that they have run the Rotax 912 to 5K hours without any major issues, why are you so concerned with wanting to dry out the air when this engine can go this many hours without major issues? It seems most people who operate them just follow the Rotax M/M recommendations with good results. Of course you can pursue what ever actions you think will enhance the operation but is it really needed?
 
The design of the Rotax as everyone is describing doesn’t allow air into the engine. In fact if you do an oil change incorrectly and allow air into the system, you have to pressure purge the system. Failure to do this can cause catastrophic issues including engine damage requiring replacement. So the dryer filter doesn’t apply to the Rotax design.

I saw that in the video and I understand it. But you and others are mixing two issues. The issue of the oil vent is one issue. The issue of the super-moist hot air cooling and leaving behind condensation is an entirely different issue and is necessarily applicable to all our engines, Rotax included. Until we switch to a fuel that does not produce water vapor when burned, it will be so.

When you "burn" hydrogen (H) you are combining it with oxygen (O). H2O is water. The other major component is, of course, CO2. The carbon and oxygen are the major components of our fuels.

When you heat the oil you boil out the dissolved water. But, when the hot, moist air inside the engine cools, condensation MUST happen. You just put the moisture back in.

The maximum amount of water vapor in hot air is much greater than the maximum for cooler air. Think fog on steroids. While most of the exhaust does go out the valves, some blows by the rings either at the cylinder walls or at the ring gaps which are designed into every piston engine to allow for thermal expansion.

Some designs produce (or leave) more condensation than others. Old, small Conti's produce a lot, judging from anecdotal accounts. The small (1300 cc's) Rotax seems to produce less but what it does produce is hidden inside the area for the crank and the rods, etc.

https://www.engineeringtoolbox.com/maximum-moisture-content-air-d_1403.html

The need for injecting dry air is still there even if the way to do it is a problem. The Rotax has the need just like any other Otto cycle gasoline engine.
 
I've heard that they have run the Rotax 912 to 5K hours without any major issues, why are you so concerned with wanting to dry out the air when this engine can go this many hours without major issues? It seems most people who operate them just follow the Rotax M/M recommendations with good results. Of course you can pursue what ever actions you think will enhance the operation but is it really needed?

It is common knowledge that engines which are operated often with short intervals of down time are the most likely to go to TBO and beyond. The problem with leaving condensation inside the area of the crank and rods, etc. is that moisture which is left on ferrous parts for a long time is most likely going to cause corrosion.

I only flew my 7A <270 hours in 16 years. I'm getting old fast or I wouldn't be flying a 12. It is likely that my 12 will have long periods of down time. Also, it probably won't fly much or at all in the winter. The only good news about winter is that the air is inherently dry and if you keep the engine warm (I do) then the possibility of rust is greatly reduced.

I hope this explanation will help others sort out the problem and its causes from all the "evidence" that keeping the inside of the engine dry isn't needed.

This article may help clarify the problem.
https://img1.wsimg.com/blobby/go/c3...loads/Test Article 2065.pdf?ver=1660739764737
 
It is likely that my 12 will have long periods of down time. Also, it probably won't fly much or at all in the winter.

I get that you are obsessed with moisture in the engine... You will have a bigger problem with long inop periods if you use MOGAS w/ alcohol. Several threads on the subject in this forum. MOGAS does not have good shelf life loosing octane, causes varnish, and alcohol separation with water absorption. Best to use 100LL which has excellent shelf life but causes add'l maintenance when used in Rotax 9-series engines. Lead is not good for gearbox and slip clutch. Also, oil tank requires cleaning because lead fouls internal screen.
 
There are RV-12's for sale and "out there" for the past 3 or 4 years since I was looking and bought one, completed from 2009 to when ever, with 60 or 70 hours on them. I bought a 2012 in 2020 with 170 hours on it. Owner was based in Hilton Head, SC, plenty humid. There's LOTS of RV-12's based in Florida. As well as other experiemental model planes based in the Rotax 912 series motors.

The problem you are seeking to solve, corrosion of some sort inside the motor, just doesn't appear to exist, for all these other Rotax 912 motor owners.


But have at it, it is an experimental plane. I don't know much about planes, I know enough about gas powered motors, but, from my limited experience, you're looking to solve a problem that doesn't exist yet, at least not yet on a 912 Rotax. There's theory, as you explain, and then there is reality, where a real problem exists. Rotax motors aren't seeing corrosion like older Lycoming and Conti designs.

I'd suggest you call a Rotax repair shop down in Florida, that rebuilds Rotax, and speak to them about internal corrosion problems with Rotax 912 engines that they've built, before proceeding with your time spent on experiments. Lockwood Aviation, I believe, is the name of the place.
 
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I get that you are obsessed with moisture in the engine... You will have a bigger problem with long inop periods if you use MOGAS w/ alcohol. Several threads on the subject in this forum. MOGAS does not have good shelf life loosing octane, causes varnish, and alcohol separation with water absorption. Best to use 100LL which has excellent shelf life but causes add'l maintenance when used in Rotax 9-series engines. Lead is not good for gearbox and slip clutch. Also, oil tank requires cleaning because lead fouls internal screen.

I don't know why you feel you need to provide this information but since you did I will offer some additional information about this new subject.

I spoke directly with Lockwood about the problem of mogas with ethanol. I was told that it is OK to use products such as StaBil to significantly extend the useful life of premium auto gas in sealed cans in my hangar. The eventual loss of the ethanol directly lowers the AKI (octane rating, sort of). The StaBil is OK to use in order to prevent it.

btw, I agree that the mogas AKI is a serious issue for this airplane. I also agree that avoiding 100LL as much as possible is the best thing to do.
 
There are RV-12's for sale and "out there" for the past 3 or 4 years since I was looking and bought one, completed from 2009 to when ever, with 60 or 70 hours on them. I bought a 2012 in 2020 with 170 hours on it. Owner was based in Hilton Head, SC, plenty humid. There's LOTS of RV-12's based in Florida. As well as other experiemental model planes based in the Rotax 912 series motors.

The problem you are seeking to solve, corrosion of some sort inside the motor, just doesn't appear to exist, for all these other Rotax 912 motor owners.


But have at it, it is an experimental plane. I don't know much about planes, I know enough about gas powered motors, but, from my limited experience, you're looking to solve a problem that doesn't exist yet, at least not yet on a 912 Rotax. There's theory, as you explain, and then there is reality, where a real problem exists. Rotax motors aren't seeing corrosion like older Lycoming and Conti designs.

I'd suggest you call a Rotax repair shop down in Florida, that rebuilds Rotax, and speak to them about internal corrosion problems with Rotax 912 engines that they've built, before proceeding with your time spent on experiments. Lockwood Aviation, I believe, is the name of the place.

No matter how much I explain the source of the moisture, you and others insist that the local ambient humidity - such as in Florida - is relevant. If it is, it's only marginally the issue. The issue is the moisture that is created by the burning of gasoline.

That there are lots of Rotax engines that don't have corrosion - as far as anyone may have reported - does not really prove or disprove the physics.

I started this thread asking two simple questions. Only one person answered me directly and he or she has been a big help.
 
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