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Oil film on belly of aircraft

DJP

Well Known Member
The guy that I bought the aircraft from wrote a list of some of the things about the aircraft that he gave me when I took ownership. Down on the list it said something about the engine being happy with a oil level of 6 quarts. Since it holds 12, I thought that must be a typo, that he really meant 9 quarts. Over the last 700 plus hours of operation, I have let the oil level slowly come down, trying to find a level where the breather stops blowing oil out, putting a film on the belly of the aircraft. I am now at 6 quarts and it is now pretty much stopped the film on the bottom. Being concerned about that level I contacted Lycoming and talked to a tech about it. He asked about temps and they are all normal. He said the the factory answer is a minimum of 2.75 quarts. He said that some IO-540's have a 8 quart sump, mine happens to be 12. He suggested talking with other IO-540 owners to find out what their experience has been, so here is my post. I am sure that others have had oil on the belly of the airplane, I just wonder how they got it to stop, if they did. I wondered if a different type of breather might help but the tech didn't think that would make a difference.
 
I?ve never flown a plane that didn?t get oil on the belly, so it?s fairly common. Every engine is going to have a different ?stable? level. A few of my friends all with IO-540 have different levels, one is 9... one is 7. I?m only 20 hours in and will determine mine over the next 20 hours. Right now I?m at 8.75.

I plan on installing an oil separator and vacuum from Antisplat after engine break-in once I determine my IO-540 ?normal? oil level.
 
Belly oil

O540 A1A for 450 hours. Stopped spitting at 6 quarts so ran it there from then on. Never had high temps, it seemed to really like it there. Anything more and it spit all of it out above six
 
Minimum is 2.75 quarts. Lycoming also says that the maximum oil burn is one quart PER HOUR! Yeah... you should be looking deeper into the engine if that is happening.

Anyways, if you have 4 hours of fuel on board then 2.75+ 4 (at one qt per hour) is 7.75 quarts minimum.

Take that FWIW...

From a practical aspect, If you burn one quart every 15 hours or so like most of us, then six is just fine.

:cool: CJ
 
I have read the 2.75 quart number as well but have never ran below 8 and yes I get oil on the belly. I spent Sunday scrubbing the belly.

I have filled to 12 before and it does blow it out to around 9-10 in a couple of hours. I have filled to 10 for many years and it seems like it uses/blows it on the belly pretty consistently.

If it it is stable at 6 and temps are good that is an interesting question. I would want to know why though before I ever ran there? It is absolutely not turbulence as I have it put it on the belly no matter how smooth my flights have been. How does having oil above 6 get blown out?
 
Removing oil from the belly . . .

The first question I have for those who commented is "are you using an oil separator"? Having built numerous oil separators over the years I have many happy customers using my designs. There are commercial ones out there that are not that effective. Successful oil separators change the direction of the breather air numerous times. I build models that turn the air 360, 450 and 540 degrees, naturally the more turns the better. So what do you do with the oil it collects? I recommend putting it back into the sump below the sump's oil level. Others collect it in a bottle or dump it into the exhaust (the exhaust does not save oil consumption). Regarding my method, you'll get the argument that your putting contaminants back into the oil and that's true; however, frequent oil changes presents no problem. I have been sending my oil in for analysis for 20 years and I have yet to receive any comments on the sample other than "normal". Personally, on my 8 quart sump I wouldn't run my engine that lower than 6 qts.

As a side note, one of the reasons manufacturers have more oil than the minimum is to lengthen the oil change interval since your engine is constantly putting contaminants in the oil.

Remember, one thing an oil separator can't fix is an engine with mechanical issues.
 
breather tube

Just a thought but why do breather tubes have to terminate in the front of the plane. Why can't a tube run through the fuselage and exit oil out the tail? Is it a fire hazard? Just thinking out loud.
 
I have read the 2.75 quart number as well but have never ran below 8 and yes I get oil on the belly. I spent Sunday scrubbing the belly.

I have filled to 12 before and it does blow it out to around 9-10 in a couple of hours. I have filled to 10 for many years and it seems like it uses/blows it on the belly pretty consistently.

If it it is stable at 6 and temps are good that is an interesting question. I would want to know why though before I ever ran there? It is absolutely not turbulence as I have it put it on the belly no matter how smooth my flights have been. How does having oil above 6 get blown out?

My RV-10 has settled in to a level slightly above 6 qts. It's been very stable at that level for the last few years. It's hard to be more precise, since the dipstick markings go from 6 to 9. Not very accurate.

Flying locally I'll leave the level around 6. If I fly cross country, I'll add a quart knowing that over the course of the trip a fair amount will end up on the belly.
 
Just a thought but why do breather tubes have to terminate in the front of the plane. Why can't a tube run through the fuselage and exit oil out the tail? Is it a fire hazard? Just thinking out loud.

If you don't mind the extra weight of the tube, and the nuisance of routing it through the structure internally in a straight path to the tail (no kinks or bumps to trap oil) then it can. Exit just in front of your tailwheel and it'll never need lubing again...
 
Engine Breather Venting

Be vary careful venting the engine breather tube down the gear leg or through the fuselage to the tail. When temperatures fall below freezing it will freeze shut. The result is oil on the windshield and rapid loss of engine oil out the crankshaft seal.
 
Oil level at the level it stays

I struggled with the oil being run under 8qt for the first few dozen hours, once the engine broke in I called my engine builder and he told me to fly the plane and see where the oil stopped. It stopped right under 6qts, I now run 6 qts of oil for over 500 hours and the temps have stayed normal and the engine has worked great.
Good to see Im not the only one running it that low.
My suggestion- fly until the oil stabilizes for over 2-3 hours if it stays around X level, fly it at the level, adding up to that point as needed.
Pascal
 
The first question I have for those who commented is "are you using an oil separator"? Having built numerous oil separators over the years I have many happy customers using my designs. There are commercial ones out there that are not that effective. Successful oil separators change the direction of the breather air numerous times. I build models that turn the air 360, 450 and 540 degrees, naturally the more turns the better. So what do you do with the oil it collects? I recommend putting it back into the sump below the sump's oil level. Others collect it in a bottle or dump it into the exhaust (the exhaust does not save oil consumption). Regarding my method, you'll get the argument that your putting contaminants back into the oil and that's true; however, frequent oil changes presents no problem. I have been sending my oil in for analysis for 20 years and I have yet to receive any comments on the sample other than "normal". Personally, on my 8 quart sump I wouldn't run my engine that lower than 6 qts.

As a side note, one of the reasons manufacturers have more oil than the minimum is to lengthen the oil change interval since your engine is constantly putting contaminants in the oil.

Remember, one thing an oil separator can't fix is an engine with mechanical issues.

I too want to hear more about your separator...
 
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