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How is the oil getting out?

N29945

Active Member
Background Purchased RV6A, O-360, constant speed prop, 550TT, new engine and prop at build, 2002, compression are all 74/80 or better cold, I use 100LL, the exhaust pipes ore dry and chalky gray in color,
there is no puff of white smoke when the engine starts after setting several days, the engine has an air/oil separator, there does not appear to be a lot of oil leaking anywhere from the engine or on the engine. There does not seem to be a lot of oil on the belly, there is no oil dripping from the belly, however the belly seems to be covered with a light mist of oil, again rarely is there oil dripping from anything.
When I change the oil, I change the filter, add 6 quarts of oil, 1 pint of Camguard, leak check, fly the airplane and then service it back to six quarts.
My shortest flight is usually 30 minutes, longest flight two and a half hours.
The problem.... the engine disposed of about a quart of oil every five hours, were is the oil going, is the air/oil separator defective and somehow pressurizing the engine and somehow misting the oil out of the engine?
Thanks for you insight in advance.
Jim
RV6A
Exempt but privileged to donate, then I get to ask questions and get meaningful answers.
 
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Oil leaves in 3 possible ways: leaks, blown out the breather as mist or burned off the cyl walls during combustion.

If the separator is doing it's job, losing 1 qt in 5 hours is probably not due to leaving out the breather, though that is still possible as a separator can only handle so much oil. Losing oil out of the breather is typically due to too much blowby, which is usually caused by issues with the compression rings. the air inside the crankcase is filled with oil mist. With too much blowby, it forces that air out and it takes the oil with it in mist form. Typically a lot of that oil collects on the belly.

Most likely you are burning the oil. When the cylinder walls and the rings are in perfect condition, you lose little oil to burning. When less than optimum, not so much. There are various conditions that can cause this with different levels of oil loss. None are easily addressed. Examples are glazing of the cyl walls, loss of cross hatch on walls due to excessive wear, broken rings, poor break in of ring / wall interface, etc. When the oil is burned in small quantities like this, there are usually no signs of it. When it becomes excessive, you will see oilly residue on the plugs, especially after periods of idling (it burns off the plug at the higher temps seen at higher RPMs, assuming yiou have the right sparkplug temperature rating). Sometimes a borescope will show pooled oil on the cyl wall at the top of the piston at the lowest point; gravity moves it there.

Also, a plugged oil return line from the rocker box will flood that area and introduce excessive oil into the combustion chamber via the valve guides.

Larry
 
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It leaks by the rings while the engine is running and goes out the exhaust. Mine uses about a quart every 7 hours, some people get 20 hours per quart or more. I don't want to call it a design flaw, but this style engine will always burn oil. Nothing wrong with it until it gets excessive.
 
If it is blow by you can check your plugs to see if you have oil on them.

Blow by does not leave oilly plugs. Blow by by definition is a ring or ring/wall interface issue that allows compressed gasses past the rings into the crankcase. These gasses pressurizes the crankcase, causing that air to leave via the breather. Every engine has blowby, though not excessive when things are as they should be. Excessive oil left on the cyl walls is the typical cause of oilly plugs, as is bad valve guides or seals on vertically oriented cylinders.
 
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One path for excess oil consumption is worn intake valve guides. There is always a vacuum in the intake valve port while the engine is running. This vacuum sucks some oil from the rocker box past the guide helping lubricate stem and guide. If the clearance becomes excessive it will suck too much oil and can increase observed consumption.
 
All engines, especially aviation engines, use some oil. 1 qt in 5 hours for a 360 is higher than average but it is not excessive.

When you fly for 2.5 hours, do you get the same burn rate, about half a qt?

Short flights tend cause to lose more oil than longer flights.
 
An air-oil separator may not overcome a poorly located breather exit- could you post a pic of the location of yours?

Until I found the right location, I had a pressurized system- I had tried to locate the breather where it would have efflux vaporized on an exhaust pipe. I had to go about 4 inches lower and bevel the exit back 45 degrees, now my same oil ritual as yours has a no-leak engine and 20 hours/Qt. No air-oil separator.
 
oil burning O-360

What cylinders do you have? Are they Channel chrome? They are known for oil burning. You don't need leak detector as the oil glows in the dark.
Also, if you do not think you have oil leaks maybe you aught to check the engine with a black light in a dark hanger.
I thought I didn't have any real leaks either, till I got out my black light. OOOPPPSS look at all that color up there. Yes I had a leak and it was blowin in the wind. Backup alternator pad was leaking.
I have an 2001 RV-6A O-360 CS prop SDS fuel and ignition systems 550 hours CHANNEL CHROME cylinders and use a quart in 6 20x50 Phillips. Changed at 25-30 hours. Filled to 6 quarts burn down to 4 then add one quart.
Not going to do anything about the oil use cause them cylinders are known to burn oil.
My three cents worth Art
 
What brand

Not really sure what brand it is, but after reading these posts and another day of exploring the air/oil separator is suspect.
 
Not really sure what brand it is, but after reading these posts and another day of exploring the air/oil separator is suspect.

If you are going through a quart in 5 hours and all of it is going out of the breather, I would not expect ANY separator to catch it all and also would expect quite a bit of oil coating the belly. Separators are made to deal with only moderate amounts of air passing through them. If you have a lot of blowby it will overwhelm the separator and it will not work effectively.

If you truly are blowing a quart out of the breather in one hour, a compression check will likely confirm that. I don't believe that a cyl measuring 78/80 can cause that much blowby. On my 540, I found a cracked top compression ring (50/80 compression) on one cylinder and was only consuming a quart in 10-15 hours due to blowby. If compression's are all good, it is more likely you are burning the oil. If you eliminate leaks and blowby, the only option left is burning and there are only two common ways for that.
 
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I love this question. Not because I have any answers but because I'm in exactly the same place. Nevertheless it may help to hear my experience.

My engine is also O-360, normally aspirated. Consumption has always been a bit high at around 8 hrs/qt but by 1500 hrs or so it had dropped down to 1 in 3.5 hrs. Borescope inspection showed some pitting on all the cylinder walls, not excessive but it was thought that was the cause. Pulled the cyls, had them honed (still to new specs) and new rings. Since then I'm getting closer to a qt in 5 hrs. So, better but nyah?

Like you all the traditional indicators seem fine. I looked for answers everywhere including calling into the Ask the A&Ps podcast (Mike Busch of course chastised me for pulling the cylinders but I maintain that it was worthwhile for the educational value if nothing else.) Anyway they weren't a lot of help. One thing I do regret was not having the valve guides serviced when I had the cylinders off as I suspect that's where the oil is still going. Ah well, not doing that again, and anyway that could be done in place if I decide to.

Anyway 1 qt in 5 hrs is still well within specs so just annoying at this point. I get good compression, good power, runs great. I'll do a wobble test at some point, maybe check cranckase pressure if I can find an old altimeter, and go from there. Meanwhile I fly and have fun and try not to obsess about it.
 
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Brand

It will likely soon be an Aero-Splat, the unit that is on there now is a rather large black thing with many feet of many different size and length of hoses...
 
It will likely soon be an Aero-Splat, the unit that is on there now is a rather large black thing with many feet of many different size and length of hoses...

Maybe just go with the breather that Van's shows in OP-27, OP-34, OP-35...before you add more money to the equation...
 
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