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How much oil on the belly?

Jamie

Jamie

Well Known Member
Ok, I admit it...my plane has an oily belly.

I have an XP-360, standard mags, no inverted oil system.

I always accumulate wet oil on the belly of the plane. It's not enough to really see on the oil stick...I always run at 6qts and it stays right there between oil changes. I really never have to add any oil.

I never do negative g maneuvers. I do fly a lot of acro, but it's always limited to positive g stuff (almost always just rolls, cubans, wing overs, etc).

So how much wet oil is usual on the belly?

I do not have an air/oil separator, but after searching here on VAF I do not believe that it is the panacea that the air/oil separator manufacturers claim.

I have tried to trace down if I have a leak in the engine, but to no avail. I have used the dye and a blacklight...again...I see nothing after ground runs.

My breather tube runs to about 1/2" from the exhaust. Should I get it closer? Would this really make a difference?

Just looking for ideas here.
 
My breather is about 1/4" from the exhaust - judging from the clean(ish) belly and the burnt cruft on that exhaust I think it must be helping.

Do you add a qt when you reach 6 qts on the stick? For local flying the rule I use is add a qt when it gets to 5 on th stick. For XC I make sure that I have at least 6 qt in the engine

Back when I used to add at the 6 qt level, the belly got much oilier when I did loops (I guess that .5 g at the top is a little bit too floaty). Less than 6 seems to make things go much better.
 
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Great question! I only have 20 hours on my aircraft, but was wondering exactly the same thing. I have been toying with getting an oil separator, but don't have any experience with them and hadn't made up my mind yet. I too have a Superior IO-360 that doesn't seem to burn any oil. With my 20 hours on the new engine, I have yet to add a full quart. (I've been running it at about 6 1/2 quarts.) I had hoped that running the oil breather line over the exhaust would "burn it off" as Van suggests, but that doesn't seem to help much. I been flying positive g aerobatics as well, but even on the flights I don't fly aerobatics I still get oil on the belly.

Mark
 
"I do not have an air/oil separator" ... I'm betting it will help your problem.
I'll be installing one on mine.
My .02
 
As for new planes without oil separators:

WAIT!

Back when my RV was new it blew a bunch more oil on the belly and I thought I'd need to add a separator. The combination of 50 hrs of flying to seat rings etc, carrying a little less oil in the engine and moving the breather closer to the exhaust fixed all my oily belly problems.

I'm _so_ glad I never went back to add that bulky separator and plumbing.
 
Kevin,

Thanks for the info. I think I'll do exactly as you recommend--run between 5 and 6 qts in the sump, and see about moving my breather line a little closer to the exhaust.

Mark
 
Water mist, oil mist mixed with water mist, acid fumes, and other garbage comes out of the breather. Try as they might, the separators do not return perfectly clean oil back and let all that other crud out. A separator might keep the belly cleaner but it does so with a insidious cost to the engine.

Cars deal with this very effectively by routing the breather to the air intake, aka PCV. Not even a remote option for our application.
 
I'll try moving the breather tube closer. I do notice a fair amount of crud on the left exhaust pipe...and all of the oil seems to be coming out of the left side so I imagine it's all coming from the breather and it's not a leak somewhere else.
 
We initially also lost a fair amount of oil onto the belly, albeit in aerobatics... If you really do only do +ve 'g', then might sound OK, but any roll / vertical pullup (even a loop) is going to see oil into the breather :eek: (think 1/3 of the way round a loop - yes +2g vertically pulls the oil to the bottom of the engine, but horizontally also to the "back of the engine" where the breather is...).

If you do want to do lots of aerobatics, don't want to clean the belly, don't want a full inverted system, consider half an inverted system. We now have the (Raven) Oil Tank with the "breather in", and the return to the sump hose + standpipe. It reduced the oil on the belly by a lot - although it can still be defeated :( It does not, of course, provide a positive oil feed to the engine under negative 'g' - it just saves oil/mess ;)

Andy & Ellie Hill
RV-8 G-HILZ
 
I don't think your logic here about 2 g's vertically pulling the oil to the bottom of the pan is accurate. It acutally stays in the same place at anything greater than 1 g. The g-force during the loop is actually perpendicular to the line of flight. Think about how you personally feel it in the cockpit. The g's are still felt in the seat as you go around the loop (keeping everything positive). They don't transition to your back when you go vertical unless you continue straight up by relaxing the pull on the stick.
That aside, I have found that the Airwolf oil breathers are the absolute best, but they are very expensive. The only crud ont he bottom of my RV-10 was lead from the exhaust. No oil at all.
Vic
 
A couple of years ago I got an email from a gent down under who told me that some of the RV'ers in Oz have removed a gear inside the case of their Lycomings that resides somewhere near the access. mounting for a vacumn pump. The theory was that this gear was splashing oil into the breather tube and putting it overboard. Without the gear the planes bellies were staying oil free. This seems like the way to have an engine built with the glass going into most RV's these days instead of gyros. Having never seen the inside of the engine I have no idea what gear, or if we can just off load parts this way. How about it, any engine guys who can validate or debunk this?
 
I had the same problem and solved it with two simple solutions.

1. My superior engine immediately spits out anything over 6qts. Made sure that I run her between 5 and 5.8qts.

2. The oil breather tube, next to the exhaust, points backwards. This creates a venturi and sucks oil out of the engine (albeit very little). I solved this problem by drilling a hole in the front side of the breather tube just where it comes out of the cowl.

Problem solved. And I spend more time doing 4.5g aeros than straight ad level.
 
I don't think your logic here about 2 g's vertically pulling the oil to the bottom of the pan is accurate. It acutally stays in the same place at anything greater than 1 g. The g-force during the loop is actually perpendicular to the line of flight.
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I would agree, provided you do your Loops with the engine off / idle :eek:

In practice, in the "Vertical Up", you are not decelerating at 1g, but 1g - Thrust.. therefore the overall vector is somewhat aft of perpendicular due gravity.

Secondly, whilst you might pull 4g at the bottom of the loop, a figure of 0.5g is more typical over the top... Combined with the Thrust effect at low speed, that vector is getting more aft...

But whatever, the bl**dy oil does come out, and any solutions that reduce it are worth discussing :D

Andy
 
I too had a oily belly early on... getting the breather tube closer to the exhaust pipe and settling on the 6 qt. level helped..But didn't totally stop the oily belly... It helped too,quite a bit, when I installed an oil breather system... I send the collected oil from the breather into a small bottle on the firewall not back into the engine... This is a way to watch the blow-by amount.... l dump it when I remove the cowl... Usually fills in about 10 - 12 hours which is usually the time I tend to remove the cowl anyway... The plumbing is quite simple in that the breather collector is just cut in between the normal breather tube that runs down near the exhaust pipe and a small ( 1/4") tube to the collector bottle..
 
Bryan Wood said:
A couple of years ago I got an email from a gent down under who told me that some of the RV'ers in Oz have removed a gear inside the case of their Lycomings that resides somewhere near the access. mounting for a vacumn pump. The theory was that this gear was splashing oil into the breather tube and putting it overboard. Without the gear the planes bellies were staying oil free. This seems like the way to have an engine built with the glass going into most RV's these days instead of gyros. Having never seen the inside of the engine I have no idea what gear, or if we can just off load parts this way. How about it, any engine guys who can validate or debunk this?
Click to expand...

I think Bryan is referring to me as the likely foreign suspect although I think it was this thread rather than an email. http://www.vansairforce.com/community/showthread.php?t=21824.
Now with about 150 hours of flying I can't say for sure if it helps the dirty belly. One thing I have noticed is that the orientation and position of the end of the breather seems to make a difference for me. As per the above link my breather terminated over the exhaust pipe and I cut the end of the breather so that it paralleled the downward slope of the exhaust pipe. This meant that the open end of the breather faced into the airflow exiting the lower cowl. In this configuration I was using virtually no oil even with the level over 6 ltr. Due to a leaking main crankshaft seal and the possibility that the breather arrangement was pressurizing the crankcase, I subsequently extended the breather down into the cowl outlet and faced the breather outlet in the opposite direction so that the airflow should suck on the breather. With this arrangement, anything over 5 ltr in the sump will result in a rapid loss of oil on to the belly.

Fin
9A
 
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Breather hose end orientation

What is optimal? Sounds like anything that allows pressurized air in may be bad.

Should the end be horizontal?

Vertical with the opening facing aft?

45 degree to horizontal with the opening facing aft?
 
Look for leaks

My friend and I built a Superior O-360 engine for my 9A. After 100 hours, the front seal started to leak. The belly got oily. For $13.25 for a one piece seal from Spruce and 2 hours of work, the belly is a lot cleaner.

Look for leaks.

Barry
 
Finley Atherton said:
I think Bryan is referring to me as the likely foreign suspect although I think it was this thread rather than an email. http://www.vansairforce.com/community/showthread.php?t=21824.
Now with about 150 hours of flying I can't say for sure if it helps the dirty belly. One thing I have noticed is that the orientation and position of the end of the breather seems to make a difference for me. As per the above link my breather terminated over the exhaust pipe and I cut the end of the breather so that it paralleled the downward slope of the exhaust pipe. This meant that the open end of the breather faced into the airflow exiting the lower cowl. In this configuration I was using virtually no oil even with the level over 6 ltr. Due to a leaking main crankshaft seal and the possibility that the breather arrangement was pressurizing the crankcase, I subsequently extended the breather down into the cowl outlet and faced the breather outlet in the opposite direction so that the airflow should suck on the breather. With this arrangement, anything over 5 ltr in the sump will result in a rapid loss of oil on to the belly.

Fin
9A
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Yeah Fin, I was hoping I could get you jump in and clarify this. I didn't remember that it was from a post however and couldn't remember the exact details.
 
Just to clarify post # 16. Changing the orientation of the end of the breather so that it should not have been pressurizing the crankcase did nothing to solve the leaking main seal. Two new seals later and a bit of magic from my local engine man solved the leaking seal.

Fin
9A
 
Ha! Told you not to paint that belly white, Jamie! A nice navy blue down there and you'd never notice.

I chased oil leaks in my old Mooney constantly. I have nothing really to add other than don't be afraid to take your oil level down a little to test - 5 qts or so. I think Lycs can run on something like 2 qts in the sump (but I wouldn't go that low!)
 
Problem found!

I finally found the source of the abundance of oil on my belly. My breather hose setup was simply not tight at the engine. A friend of mine found wet oil under the hose attachment point. I tightened down the Breeze clamp and have made about 10 flights since and oil accumulation on the belly is dramatically decreased. In fact, I don't see any oil at all between the firewall and the main wing spar. Aft of the spar I am still seeing a little oil, but I believe it is leaking out of crevices and will eventually go away. In particular, I believe that I have oil between the wing and the lower wing fairing. I will try to clean out those areas at annual next month.
 
Ok, so the breather wasn't the source of oil on my belly. It was the legacy fitting directly beside the breather on the accessory case where the oil filter adapter attaches. I put a new crush washer under that fitting and so far I am seeing much, much less oil on the belly. I think I may have it nailed down -- finally.
 
I have an oil seperator and I still have oil on the belly

I have a seperator from day one and I still have oil on the belly. What I was going to do was to change my breather tube to extend beyond the rear facing scoop and hang out like the exhaust pipes do. This to try and get the fumes and oil to fly out past the scoop and hopefully not get as much on the belly. Mine drips onto the inside of the lower cowl also so I hoping to stop this. I'll let you know how it works out. I wanted to do like the airobatic guys do and run the breather all the way out the back of the plane. The problem is getting it back past the spar. If you have a hump in it to go over the spar your going to get a buildup of oil and a blockage I think.
 
legacy fitting?

Jamie, I've had a small but persistent oil leak that I haven't been able to find. Where is the fitting you referred to and what does it look like?
 
Rick_A said:
Jamie, I've had a small but persistent oil leak that I haven't been able to find. Where is the fitting you referred to and what does it look like?
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The fitting needs a 1" socket/wrench. On my XP-360 is is directly under the breather tube and is safety-wired. The oil presence at the fitting was minimal, but there was a lot more visible on the accessory case where it was running down. If you don't have oil on the accessory case I doubt this is your problem.
 
Long Breater?

In the most recent Sports Aviation there is an article on a group of guys with Pietenpol?s or something like that. Haven't read it yet...but in one photo they point out one pilot ran his breather all the way through the fuselage and out along his tail wheel. Looked like a pretty clean and seamless way to solve the problem...which of course means it CAN'T be that simple. lol.

Not something I am willing to do on a whim...but the idea is intriguing enough to warrant comment here. Other than the routing, what would the downsides be?
 
wera710 said:
In the most recent Sports Aviation there is an article on a group of guys with Pietenpol’s or something like that. Haven't read it yet...but in one photo they point out one pilot ran his breather all the way through the fuselage and out along his tail wheel. Looked like a pretty clean and seamless way to solve the problem...which of course means it CAN'T be that simple. lol.

Not something I am willing to do on a whim...but the idea is intriguing enough to warrant comment here. Other than the routing, what would the downsides be?
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Scott,

Adding a long hose like that also adds a lot of extra weight. In addition, you will have to find some place to route it through the firewall, the front spar, the rear spar, over or through all the bulkheads, and finally out the tail.

Van's set up is much cleaner.

Installing such a line on a tube and fabric (or wood and fabric) high wing (or bi-plane) is much easier because you typically don't have bulkheads or spars inside the fuselage.
 
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wera710 said:
In the most recent Sports Aviation there is an article on a group of guys with Pietenpol?s or something like that. Haven't read it yet...but in one photo they point out one pilot ran his breather all the way through the fuselage and out along his tail wheel. Looked like a pretty clean and seamless way to solve the problem...which of course means it CAN'T be that simple. lol.
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On the contrary. Many Pitts have that same tube running down the belly inside the airplane. It does keep the oil off the fabric, and at the same time still keeps the tailwheel lubricated. My recollection is that a former Pitts owner told me that the line is prone to getting condensation in it and freezing in colder months/climates. But I forget the details. If there was a route through the fuselage that would let me do this, I would be inclined to try it... Polishing the skin that has oil all over it is a pain in the b*tt.
 
Pitts / Extras etc. all run breather out to near tailwheel.

The One Design I have a share in runs the breather into the exhaust. I would never have done that without knowing more, since the pressures are surely important? But it seems to work well i.e. engine runs fine, and no oil on the belly...

With the RV-3 I'd like the either run the breather to the tail (weight :mad: ) or put it into the exhaust. Can anyone with more knowledge than I comment on the desired / undesired pressure aspects of the breather v exhaust?

On the RV-8, the breather pipe almost touches the exhaust - for those going this route, it is a soft AL pipe on a SS pipe, so I see no issue in them touching, 1 will "wear" itself into shape ;)

As an aside, the breather to tail idea I would avoid for those with the funny wheel at the front - you need the breather to drain water etc. using the natural geometry of the aircraft, water freeezing in there could spoil your day :eek:

Andy
RV-8 G-HILZ
RV-8tors
 
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