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Oil Consumption and Breather Tube

Bill.Peyton

Well Known Member
Now that I have around 45 hours on the engine I still find that I am consuming around 1 qt every 7 hours. I have been topping the oil off at 10 quarts. I am thinking that I may be running too high an oil level.
I ordered one of the air/oil separators, but I am now thinking that I don't want to install it until I find the root cause of the problem.
I am also concerned with the angle of the breather which is pointing forward per the plans.
What experience is out there regarding oil level and consumption and breather tube installation on the 540 D4A5?
 
oil

Bill, I can't remember if you asked me this question a little while ago but someone did and now I am paying closer attention to my oil consumption. When I change the oil I put in 10 quarts. I have 2 quarts extra from the case and I usually have 0 quarts by 50 hours. At about 20 hours I show 9 quarts so I add one more at 25 hours and let it come back down to around 9 to 9-1/8 before the oil change is due again. It seems like 9 quarts is the magic number for me.
So I guess I use 1-1/4 to 1-3/4 quarts per 50 hours holding it close to 9-1/8 total.
As far as the breather tube goes, I like how mine works. It faces forward and shows a dime size drip on the hangar floor after sitting from 1 night to whenever. It seems to work fine and there is no oil residue on the firewall, however, there is a little residue on the louvers. Not saying this is good or right just another point of reference.
 
At oil change I fill to 8 qts. and by 25 hrs. I am at 7 qts. or a little less. Oil temp and pressure have been great all summer. I started out filling to 10 qts. but spent a lot of time cleaning the belly. I have a clean belly now, as my wife will attest.:D

Jim Berry
Rv-10
 
8 quarts at oil change...

I'll second the comments above. For the IO-540, anything above 8 quarts ends up on the belly of the aircraft. I don't think I even add any between oil changes anymore, which equates to about a quart and a half every 25 hours.

Brian Sutherland
N104BS (s/n 40308) 485 hours
 
OIL CONSUMPTION

I managed a flying club for 25 years and for 14 years, we had a Beech Sundowner with an 0-360K engine. It would not retain over 5 1/2 qts.

Had one pilot check the oil prior to a cross country flight of around 200 miles. Found it low and added until it was up to 8 qts. Half way back he stopped for fuel and found the oil was down to 6 qts. He called me in a panic! Asked him to check the belly of the plane as he would find two qts located there!

Three hours on an 8 qt fill up and it would be down to 5 1/2 and remain there, sometimes until time to change the oil.

This was the first engine that I had experienced this with. Our mechanic told us that every engine has a "sweet spot" and will not retain much over that amount.

Wally
RV-4 prepping for paint
 
Oil Air Seperator Effeciency

Given all the conversation of where to maintain the oil level so it won't be "overfilled" and blown overboard. Here is my question for those that do have an oil air separator. I for example run my O360 at 6 quarts, if I had an oil air separator installed and ran it at 8 quarts would the oil air separator work such that the extra 2 quarts that would be normally blown overboard, be returned to the engine or would some of it be blown out no matter what?

My thinking is that having the 2 additional quarts available for the engine would be a good thing.

I have been considering getting Anti Splats Oil Air separator. What is your experience if you have this oil air separator?
 
I have an oil seperator on my 0-360 and my opinion would be no. It helps but if you were to put 8 qts you would still lose some.
 
Fill to 7 and top at 6. On my 177A O 360 Cardinal, it was always all over the belly. I installed a Walker air oil separator & it helped immensely but not a total cure all. With the chrome top on this engine, I average 6 to 7 hrs a qt and my comp was all in the high 70's.

My RV4 with an O 360 A1A fill to 7 and top at 6. And I'm getting 25 hrs to a qt. This has an air oil separator as well and only minimal oil on the belly. Comp in the Low to mid 70's.

There is a huge variance on each engine. Anything with a chrome top (cylinders) seems to always use or lose more oil.

Tim
 
After dealing with the same issues, about 40 hours ago, i installed Antisplataero's air oil separator. I don't know why they aren't standard equipment. I now fill up to 10 qts and probably won't need to add any new oil for 50 hours. No more belly oil back to the tail. There is only oil back about 2 feet from the cowl.

At Oshkosh, I asked aerosport, Lycoming, etc. about this issue. Lycoming could only give me the book response, fill it to 10 qts. This obviously wasn't practical for me before the air oil separator.
 
Aerosport advice

Bill - I had the same question by the time I was at OSH this year. I stopped by the Aerosport tent and asked them where to run my oil. They said between 7 and 9 quarts, any more will blow out. Since I've started keeping it between 7-9 (actually 7-8), my oil "consumption" has gone down. Previous I was trying to keep it at or above 9.

One other note, which was pointed out to me by the GREAT Mike Seager: read your manual and you'll see that the "minimum safe oil level" for the IO-540 is something like 2.75 quarts IIRC.
 
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Thanks for all the feedback. Here is what I plan to do. I have the Antisplat
Air Oil sep. I am not going to install it till I try to ascertain the oil consumption over the next 25 hours with 9qts and 8 qts. I know what it is with 10. After which I may install the AI Sep to keep the belly clean.

Bryan, what type of consumption do you see?

Jchang, did you also install the valve on the exhaust?
 
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Lycoming could only give me the book response, fill it to 10 qts. This obviously wasn't practical for me before the air oil separator.

Lycoming make a great solid engine......but they also make me cringe whenever the open their mouth.

Bill, simple method.....will probably use about 100ml per hour (1qt/10hrs in your lingo).

If you are using more, the level for YOUR engine is too high.

Start at 8 Qts and do not add any....none, zip or nothing, until it goes under say 6qts, and keep an eye on the rate of disappearance.

You will see where it settles.

For us it is easier to keep it around 7 and that typically means 6.0-7.2, and if it is 6.3 and only an hour out and back, I don't add anything until i get back, then tip a whole bottle in.

Scarily they will run on 2-3 for certification testing :eek:
 
Consumption

Bill - I'll have to check but I think I'm in the 12-15 hrs per quart used at 225 on the Hobbs. Aerosport said healthy engine should use a qt in 10-15 hours. I agree with David regarding levels. I too started out trying to keep it above 9 qts but soon realized I was just wasting oil.
 
Not yet. As a temporary installation, i just ran the flex hose straight down above the right exhaust (instead of left according to plans) to see how things worked out.

One day when i get time, i may add the exhaust connection. However, without it, it has made a huge difference already on consumption and oil on the belly.

Also, my install kit came with the wrong return oil fitting. it was a size too small for the best hole in the accessory case. I mentioned it to Allan.

Also, i remember another thing Lycoming told me at Oshkosh (Jim who runs the Lycoming school). After he told me fill to 10 quarts, he said that they have engines run for hours on end with ZERO for oil consumption. I didn't get a chance to get him to elaborate more on that.

Thus, i have to wonder who is right here? zero oil consumption or the oft quoted 5 to 20 hours per quart?

Also, on this thread, we are all in agreement about anything more than 7.5 qts in the sump seems to go straight out the breather. I have heard that engines vary and see what level your engine likes. However, what's the logic here? These engines are more or less identical. Why would they vary so much in this regard?

Jae

Thanks for all the feedback. Here is what I plan to do. I have the Antisplat
Air Oil sep. I am not going to install it till I try to ascertain the oil consumption over the next 25 hours with 9qts and 8 qts. I know what it is with 10. After which I may install the AI Sep to keep the belly clean.

Bryan, what type of consumption do you see?

Jchang, did you also install the valve on the exhaust?
 
Seems like a good thread to post some data.

Recently installed an oil separator/case evacuator system on the 390. Having built similar systems for roadrace bikes back in the 80's I am comfortable with the concept.

The separator itself is very similar to the one sold by Antisplat, a nice design. Mine started out as an old Delco AC accumulator can. Just buy Allen's if you don't have a TIG and a junk pile.

2e2ja0j.jpg


The exhaust pipe tap is the usual NAPA #2-29000 smog pump check valve.
In the OEM application these valves were often installed very near exhaust manifolds, but not screwed directly into them. I think it's important to keep temperature under control if we want them to last a long time, so here you see a disc of ordinary .030" sheet steel welded to the NPT pipe bushing before the valve is screwed on. It serves as a sink for heat conducted along the 5/8' tube, and as a radiant heat shield. To reduce the possibility of exhaust header cracking at the weld, keep the 5/8 tube short, and keep the hose run flexible.

2s76e8k.jpg


Run time is now about 5 hours, not enough to firmly establish the effect on oil consumption. It does appear to be reduced. I don't know exactly how much yet. So far the stick is down a 1/4 qt or less. The belly is bone dry, as any breather oil now exits via the tailpipe. I pulled the clamped hose off the valve yesterday and poked a finger up in the tube. There was only the faintest film of oil on the tube wall.

Breather pressure was measured in flight, with the gauge tap connected near the separator inlet. The system operates at a negative 2.5 to 3.5 inches Hg, measured with an ancient manifold vacuum gauge. Typical cruise is about 2.75". A healthy Lycoming with an open breather would have a breather pressure more like 0 to 0.3" Hg positive, so the system is definitely pulling a vacuum on the case. I'd love to see one of our engine shops do back to back dyno runs with and without an evacuator, as theory says there will be a slight HP increase. Even if not, the vacuum should reduce those pesky minor case and seal leaks.

More later after some hours.
 
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Dan, Did you scarf the inner tube? I see it is mounted straight in on the exhaust tube. Bill

Cut the end at an angle? Yes, but let's consider why.

There's a tendency to think the slash cut end somehow generates low pressure. It does, but not much more, if any more, than any other shape which avoids capturing dynamic pressure.

Just for fun, I drilled a 5/8" hole in the wall of my big leaf blower's outlet tube, then made up a 5/8" tube with a pressure measurement connection on one end. The blower stream is not the same velocity, temperature, or density as an exhaust stream, but no matter. This is simply a comparison of pressure tap end shapes in a flow.

qpqfz4.jpg


Note the pressure for the 1/2' insertion of the square end, as compared to the other two ends. It doesn't make much difference what sort of end you put on your pressure tap, as long as it is not faced into the airstream. If you reverse the airflow so that the moving air impacts the open end of the slash-cut or tipped tubes, you will capture some dynamic pressure, i.e. convert dynamic to static like a pitot tube. Instead of a vacuum you would probably measure a positive pressure, not at all what we want here.

The real reason to slash cut the tube is to simply avoid dynamic pressure. The negative pressure we wish to tap doesn't stem from airflow, but rather from the positive and negative wave pressures due to cylinder events and pipe tuning.

Take a look at Figure 1 in the CAFE report titled "Aircraft Exhaust Systems IV linked fro this page:

http://cafefoundation.org/v2/research_reports.php

Note there are three points in 720 degrees of crank rotation in which a single cylinder's exhaust pipe is subject to significant negative pressure....about 10" Hg in this graph. This is the real source of negative pressure for our evacuator. The reed valve blocks the positive and we keep the negative.

BTW, my install looks like the one on the right, above ;)
 
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Link fixed above, but here's Fig 1

Credit CAFE Foundation.


o7p0z9.jpg
 
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RV10 Oil Vent Tube leaks

Now that I have around 45 hours on the engine I still find that I am consuming around 1 qt every 7 hours. I have been topping the oil off at 10 quarts. I am thinking that I may be running too high an oil level.
I ordered one of the air/oil separators, but I am now thinking that I don't want to install it until I find the root cause of the problem.
I am also concerned with the angle of the breather which is pointing forward per the plans.
What experience is out there regarding oil level and consumption and breather tube installation on the 540 D4A5?

We recently purchased an RV10, IO540, with about 300 hours. We have also been concerned with oil coming out of the vent tube after flight, and dripping on the hangar floor. We were told by a current builder of a RV10, who has built and been flying a RV7 for some years, that he removed his oil separator on the RV7 for the same reason. The consensus seems to be that we need to find the correct oil level. We are now operating at about 9 Qts, and it seems to be better so far. The forward facing opening of the tube could be an issue according to the Cessna service center mechanic we used for our Cessna 400. We would rather find someone with an RV10 that has solved this issue before we make changes.
 
My first suggestion would be to fill to no more than 8 qts. and see what happens to your breather drip. There are many posts in the archives regarding this. No need to reinvent the wheel.

I fill to 8 qts. at each oil change, and by 25 hours I am down to 6.5 qts. The belly stays clean, and all temps & pressures are normal summer and winter.

Jim Berry
RV-10
 
I allowed my oil to drop to 9 qt then monitored it. After 6 hours it was down to 8. I removed the mineral break in oil, changed the oil to Aeroshell 15W-50 since by 55 hours it should now be broken in, put in 11 qts total, one for the filter. After run up the level stabilized at 10.5. I am going to pull and inspect all the lower plugs this week to make certain that oil is not getting by the rings, then check the compression. Assuming everything is normal, I intend to allow it to decrease to 7 qts while monitoring the consumption one qt at a time. Ill report back
 
Bill, While there are no hard and fast rules here, it will be most likely that the first 3qts will disappear overboard pretty soon.

We have 730 hours of tach time, and reliably add a Qt every 10 or so hours. We now fill to 7.5 when we do a change, and that means a full amount of 7.

When it gets to 6 or close enough to there in goes one more.

You may settle on 7-8, but I would be very surprised if you get much more.
 
Me

I put in 9 at oil change, end up with 8-8.5 or so. Seems to work well, I add a quart at 7 or so depending on how far I'm flying. I've recently plotted my oil consumption and will post any useful info.
 
An aside......owners report a significant variation in oil usage rates, but it's not all due to consumption via the combustion chamber. I've never measured, but I'd bet you can note a big difference in breather oil loss merely by changing the hose routing. Quite a few are rigged with the hose coming off the breather fitting and immediately turning downward. Suspended oil droplets have a chance to go back to the case if the hose is routed up and back across the top of the firewall before turning down.

qwy1xy.jpg
 
Dan,
Good point. Kinda like a mini oil sep. BTW, how is your air/oil sep working for you, do you have enough time to tell yet?
 
BTW, how is your air/oil sep working for you, do you have enough time to tell yet?

Definite reduction in oil usage, and no belly oil mess....zip. Be aware my original breather was a "short rise" version (as in the sketch), so it's not hard to do better in both areas.

I'm now due an oil change. The plan is to track oil added over the next 50 hours, more accurate than a short term eyeballing of the stick.

A surprise is always possible, but going in my only concerns were (1) the structural reliability of the weld area at the header tap, (2) the long-term temperature resistance of the reed valve and hose end. It may take a while to be sure of either point.

It's a sump return system. I've not seen any visual signs of water; cloudy or milky oil, fill cap condensation, whatever. However, that doesn't mean there is none. For insurance I'm swapping to 20-50 Phillips and CamGuard. The non-synthetic base should suspend water better. The CamGuard is intended as prophylactic against returned acids, etc. The combination costs only a little more than a case of AS 15-50.
 
A few questions

Dan,
Like most others I have been considering an Air/Oil sep as well as a Reed valve.
If heat is a concern, why can't the reed valve be placed further away from the exhaust between 2 pieces of hose?
Having the breather hose go up as much as possible makes good sense for the reason you mentioned. Stuffing steel wool into the hose far enough to fill the riser portion of that hose would capture most of the oil mist and drip it back into the case, wouldn't it? Just an idea to maybe get away with the reed valve only.
Like most I have a drip or two after shut down not a big deal but a little annoying.
Without an oil separator would the reed valve capture a drop or two while the aircraft is sitting on the ground?
Could the hose be routed horizontal into the exhaust to have those few drops
pool inside the hose and be blown out and burned once the engine is running?
My oil consumption is 11 hours per quart, it's a good average but an air/oil sep
would probably keep the belly dry.
 
Water in oil

There is a common theme that combustion water is being returned to the sump by air oil separation systems. Given the water is in vapor form, we just need to keep the temp of the stream up through the separator to prevent water condensation, keep it as a vapor and dump it overboard. Some form of insulation on the inlet line and canister would go a long ways towards keeping it hot.

With the check valve and negative pressure in the crankcase, the flow is probably high enough to keep the inlet line and separator canister hot if insulated.

Rubber inlet hose like Dan's would seem to do the job for the inlet. I am sure there is some sort of thin spray-on material that could be used for the separator.

Not saying it is a real concern but it it is, there is an easy solution.
 
If heat is a concern, why can't the reed valve be placed further away from the exhaust between 2 pieces of hose?

It can. It may be a little less effective vacuum-wise; the hose section between the header and the reed would act as an accumulator. You would still need to be sure the hose itself can stand the heat where it connects to the header pipe.

Stuffing steel wool into the hose far enough to fill the riser portion of that hose would capture most of the oil mist and drip it back into the case, wouldn't it?

Not a good idea. Result would probably be rusty, broken shards of steel wool working back to the breather fitting and accessory case.

Without an oil separator would the reed valve capture a drop or two while the aircraft is sitting on the ground?

I dunno. It may or may not get past the reed and run out the pipe end.

Given the water is in vapor form, we just need to keep the temp of the stream up through the separator to prevent water condensation, keep it as a vapor and dump it overboard.

Agree. We're running fairly high engine compartment temperatures anyway.
 
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I'm wondering what the service life of the NAPA #2-29000 check valve might be?
I think the FAA would want on-going maintenance instructions on the form 337 if you were installing this on a certified plane?
A periodic test, inspection or replacement schedule? (NAPA 3 year 35,000 mile warrantee)
Dan, I know you are very method driven, so you must have considered this, including failure mode analysis.
 
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Quick data point.

I previously mentioned operating temperature of the NAPA 2-29000 check valve was an item of interest, given its mounting on a stub welded to a hot header pipe.

I have a pair of thermistors on long cables which I can position anywhere under the cowl. For this question I simply strapped one to the backside of the check valve flange (red, see below) with the tip against the flange, buried in heat sink grease.

Yesterday the check valve thermistor was showing around 150F. OAT was low for south Alabama, high 30's in flight. I'd expect more like 200F and maybe higher when we return to summertime. For now I'm satisfied that the valve is operating at temperatures which should not compromise its lifespan.

Do note I installed this check valve with a heat sink/radiant heat shield....the steel disk welded to the mounting nipple. As I've only measured this particular arrangement, I can't absolutely promise the same result for one without a shield. I can tell you how to check.

2lwszus.jpg
 
Oil separator installed

I installed an Antisplat air/oil separator and so far so good.
I have flown about 8 hours since and one thing is obvious, no oil anywhere
and no drip after shut down. The breather tube simply sticks out between the exhaust pipes about 3 " past the fire wall.
I now have the muffler removed to have the stub welded in.
While doing all this work at the hangar I am catching quite a bit of flak
from locals about reducing the size of the breather tube from 1 " down to 1/2" at the exhaust pipe. I am being admonished about crank case pressure and blowing a crank shaft seal if for some reason this set up won't work.
I am not concerned but the seeds of doubt have sprouted in my mind.
How many have installed the set up with the reed valve on an IO 540?
 
Ernst,
I also have installed the same. I have not flown yet. I have not installed the check valve yet. It would be very easy to measure if there is an issue by hooking up an airspeed indicator or vacuum gauge through the oil dipstick tube and measure the crankcase pressure. Measure it without anything connected to the breather port. Normal pressure is around 1.5" of water, or around 30 mph. Then attach the separator and check again. I intend to do this when I get a chance. I wonder if Alan has done this for the IO540
I am glad to hear that it is working well for you thus far.
 
While doing all this work at the hangar I am catching quite a bit of flak
from locals about reducing the size of the breather tube from 1 " down to 1/2" at the exhaust pipe. I am being admonished about crank case pressure and blowing a crank shaft seal if for some reason this set up won't work.

Typical stock breather pressures are slightly to several inches H2O positive. With the check valve breather pressure will be, ballpark, 40 inches H2O (3Hg) negative.

Tell 'em you're more concerned with sucking the front seal in. That will really spin 'em up ;)
 
Very funny, thanks.
Just because things are a little slow this time of the year, I would like to install a temporary device to actually measure the results of this installation.
Dan, just as in one of your previous posts indicated different entry positions
of the tube to the exhaust, mine is at a 30 degree angle and squard off at the end.
In order to get meaningful data I would have to measure crankcase pressure somewhere off the oil filler tube. An easier way to tap the system would be off the oil breather tube somewhere up near the crankcase breather outlet,
probably not as accurate but close.
On the breather tube it would be a simple matter of sticking a barbed sprinkler nipple into the silicone tube and run a hose to the cockpit with an pressure meter attached (airspeed Indicator).
I don't think I want to drill a hole into my oil filler tube for a hose attachment.
Any ideas?
 
An easier way to tap the system would be off the oil breather tube somewhere up near the crankcase breather outlet, probably not as accurate but close.
On the breather tube it would be a simple matter of sticking a barbed sprinkler nipple into the silicone tube and run a hose to the cockpit with an pressure meter attached (airspeed Indicator).

That's the ticket. I used an old automotive manifold vacuum gauge.
 
This is an update on the install of the Antisplat Air/oil sep.

Background, prior to the installation, 10 qts in sump would drop to 9qt level in 7 hours, 9 qts would drop to 8 qt level in 8 hours, 8 qts would drop to 7qt level in 9 hours.

I have not installed the exhaust check valve yet, just using a breather tube into air stream. I flew 11 hours (long cross country) and burned 1 qt. While 11 hours at that level is a lot better, it is not near what I thought would happen. I am still getting drips out of the breather tube, although the belly was substantially cleaner it still had quite a bit of oil on it.

I pulled all of the plugs which were dry of oil and bore-scoped each cylinder. I can still see slight honing cross hatch on the cylinder walls, which would be expected with only 90 hours on the engine. I still believe the consumption is all blow-by.

I cleaned the belly and will check out the amount of time to get to 8 qts, then 7, etc....
 
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This is an update on the install of the Antisplat Air/oil sep.

Background, prior to the installation, 10 qts in sump would last 7 hours, 9 qts would last 8 hours, 8 qts would last 9 hours.

I have not installed the exhaust check valve yet, just using a breather tube into air stream. I flew 11 hours (long cross country) and burned 1 qt. While 11 hours at that level is a lot better, it is not near what I thought would happen. I am still getting drips out of the breather tube, although the belly was substantially cleaner it still had quite a bit of oil on it.

I pulled all of the plugs which were dry of oil and bore-scoped each cylinder. I can still see slight honing cross hatch on the cylinder walls, which would be expected with only 90 hours on the engine. I still believe the consumption is all blow-by.

I cleaned the belly and will check out the amount of time to get to 8 qts, then 7, etc....

Bill,

It will be interesting to see what happens when you get to 8 qts. and below. I fill to 8 qts. after each oil change. I will be ready for a 25 hr. oil change by the end of this week, and my oil level is at 6.5 qts now. No oil added, and the belly is clean. Oil temps and pressure are normal in all regimes, summer and winter.

Jim Berry
RV-10
 
Thank you Bill for the update. Look forward to the next. I am running as low as I have ever ran right now at 8.25 Qts. It will be a while putting time on it for the next couple of months. I flew yesterday with ambient temps at altitude around 20F with damper completely closed maintaining 178F OT. CHT's around 250-260F at 65%, 30* LOP.
 
To clarify my post. If I start with 10 qts in the sump, the level took 11 hours of engine time to fall to the 9 qt level, thus burning 1 qt in 11 hours.

I spoke with Alan at Anti-splat. He agrees that there should not have been any oil exiting the breather tube and believes the reason that the separator is not working properly is the return line connection location. In fact, he feels that the only way for oil to exit and drip from the breather is if it is literally overflowing due to the lack of return to engine. Their instructions suggest and provide the fittings for connecting the return line to the unused port located on the accessory case lower right side just in front of the unused governor pad. Apparently this location had not been tested. Normally you see the return line connected with a tee to the oil return on the #5 cylinder.
My plan is to relocate the return line as above, and restart the test.
 
Their instructions suggest and provide the fittings for connecting the return line to the unused port located on the accessory case lower right side just in front of the unused governor pad. Apparently this location had not been tested.

What size hose do you have between the separator and the oil return port?
 
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