When do YOU add oil?

Part of the problem with getting a new plane after having the same old one for over twenty years is that you have to learn all it's special quirks! The O-320 in my Yankee was very boring - put in 7 quarts, and 25 hours later, drain out 5 and put in another 7...Yes, the sump held 8, but it immediately blew out anything over 6.8, and then methodically sipped it's way through the rest.

New plane - gotta learn new numbers! With 90 hours on the new O-360 in the RV-8, she is burning through about a quart in ten hours. It also seems to dump anything over a little less than 7, so putting in a quart when it is at 6 makes me need to add a quart at less than 10....but how low below 6 is reasonable? My instinct tells me that I can probably let it get to 5, but my wallet reminds me this is a brand new engine!

Sorry for being so long winded getting tothe question...what do folks that have been flying their O-360's consider to be the lowest you'll let it get? And I'd love to hear Mahlon's opinion, since his folks built the engine! (I figure I might not be the only one interested in the answer, that's why I'm posting, rather than private emailing...)

The same question on the Grumman Gang would have brought at LEAST a week's worth of debate!


Paul

Well, with my 0-320-D2A I put in 7 at oil change with a new filter. It drops to 6 and stays there for 35hrs, then between 35-50 it will drop towards 5. I try and keep it at 6 more or less. This has been working fine for 425hrs.

Oil level

I have a new O-360 in my RV-6A. I put 7 qt. in at oil change which puts it at 6 qt. when the filter is full. I usually don't let it get much below 6 qt. If I get it close to 7 qt. it blows it out.

Oil Level

I add 7 quarts when I change the oil with filter. It says 6.25 on the stick after running the engine. When it reaches 5, I typically add one but have at times let it drop as low as 4. Right now, it is sitting at 4. I have 42 hours since last oil change. I will be flying it for 1 hour or less with 4 quarts on the stick and changing the oil and filter.

Just like everyone else, more then 7 blows out.

On long summer trips, I top off to 7.

I remember reading somewhere that Lycoming required 2 quarts as a minimum. I would never fly that low and do not let it go below 4.

Gary A. Sobek
RV-6 N157GS
O-320 Hartzell
Flying SoCAL 1,839 hours.
First flight September 1997

Hey Paul,
Book says min. safe quantity is 2 quarts for vertical sumps and 4 quarts for horizontal sumps. As long as, you are not seeing changes in pressure with changes in attitude, then oil level is likely OK. Most say that having a bit extra in there, on hot days, helps with keeping oil temps down in hotter running installations. So, rule of thumb is, if the pressure stays up with attitude and the temps are OK you have an acceptable quantity in the sump.
I normally tell operators, as a general rule of thumb, to let it go down to 5-6 qts and fill to 6-7 qts. Never fill to more then 7 except at oil and filter change, at oil change time, put in 8 with a filter and cooler drain and you should end up with around seven to start off after the maintenance. If your engine doesn't put oil out the breather at 5.5 but will at 6.5 then I would run at 5.5. If it didn't put oil out the breather at 6.5 then I would run it there. The issue to me would be that I would run it at as high a level as I could, without breathing oil onto the belly. If I had an effective air oil separator, I likely wouldn't run it much below 5 on a routine basis.
Good Luck,
Mahlon
Go Steelers!
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at you own risk."

Good Info!

Thanks guys - I think I'll go ahead and let it bleed down to 5 like I did on the old O-320, and that will give me more data on the oil usage anyway. Just wanted to make sure others were running their engines that way! (I also figured this was a good way to get Mahlons thoughts on the "permanent record"!!)

I've always read that Lycoming "2 quart minimum" requirement and wondered if anyone could be brave enough to start aflight with 2.5....

Paul

Mahlon dropped this gem:

put in 8 with a filter and cooler drain and you should end up with around seven to start off after the maintenance.

Click to expand...

Mahlon, should a cooler drain be a part of the routine oil change process?

Thanks,

Sam Buchanan (still on the steep part of the learning curve..... )

Concure

About 6 qts. No more than 6.5 qts. So when adding a "qt" I would only add 1/4 to 1/3 qt. at a time usually. If I was flying cross country I would tend to keep it at or above 6 qts, local at or just under 6 qts was OK. George

PS: if you read the regs the "extra" oil is to meet a regulation about reserve oil. It made a lot of sense with oil tanks and big dry sump radials, but wet sump horizontal opposed Lycs are very happy on 6 qts. In fact the min oil is much lower. Unusable qts are two. Anything over that is "safe", but would never run with anything near 2 qts, but 5 qts or even 4 qts is not a crazy low number. I made 5.5 qts my min, but tried to stay close to 6 qts +/- 1/4. I also found anything over 6.5 qts was "throw off" at a faster rate.

Why?

mahlon_r said:

If your engine doesn't put oil out the breather at 5.5 but will at 6.5 then I would run at 5.5. If it didn't put oil out the breather at 6.5 then I would run it there. The issue to me would be that I would run it at as high a level as I could, without breathing oil onto the belly. If I had an effective air oil separator, I likely wouldn't run it much below 5 on a routine basis.

Click to expand...

Mahlon (and others),

I have an extremely simple question. Why is it that a Lyc is more likely to chuck oil out the breather at higher oil levels? I'm talking straight & level flight at some reasonable cruise power setting.

I can't visualize what's happening in there oil-wise, splashing, vapor, etc., and why the level would even affect how much escapes out the breather.

At some given power setting, if the oil pressure indication is the same at 7 quarts as it is at 5.5 quarts, what's the difference internally that's cause more oil to escape? Seems to me the same amount of splashing is going on at 5.5 as there is at 7 -- it's not like there's any less lubrication happening. Why the difference in escaped oil?

Just want to understand better.

)_( Dan
RV-7 N714D
http://www.rvproject.com

Sam, yes if you can get to it, it isn't a bad idea to drain the cooler at each change, the cooler is almost a pre-filter for the filter as unfiltered oil passes through it. So by draining it, you prevent an accumulation of any debris that it might be collecting.
If you put a T fitting with a cap on one of the T's on the oil inlet to the cooler fitting, you get backwards flow out of the cooler to the drain bucket when draining and you simply cap it with AN cap for normal use.
If it is hard to get to this, isn't a mandatory thing, and not the end of the world if it isn't done.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at you own risk."

Dan,
Think of the inside of the engine as a box about the size of two shoe boxes. The box would have a given volume of space. Now put two small holes in the box, one to pump air into the box with and one to let it vent. The one that lets air in is representing the blow by of the cylinder rings and the one to vent is representing the engine breather. Now, if we pump in a given volume of air that can vent faster then we pump it in, we have very little pressure in the box and very little air pressure out the vent. If we pump more air into the box then we can vent, we get a higher pressure in the box and more air under pressure squirting out the vent. If we keep the air supply constant and the vent constant, changing the size of the box would effect the pressure and amount of air going out the vent. Now consider the bottom of the box to be the top of the oil level in the engine. By increasing the amount of oil we have in the engine, we decrease the size of the box making it smaller because the floor of the box is rising. And by decreasing the amount of oil in the sump, we increase the size of the box because the floor is falling. When the box is big enough to handle the input air( blow by) the air in the box vents under very little pressure and the vapors of oil suspended in that air has time to settle out of the air before it exits the vent. Now, if the box is highly pressurized and the air is escaping very quickly out the vent under pressure then it carries a lot of those vapors with it.
All we are doing by running the oil level lower is making the box bigger and thus allowing the pressure build up to be less. By overfilling with oil, we make the box smaller which allows the vapors to be pushed out the vent easier.
The box isn't big enough on most Lycoming engines because as George pointed out, the oil level required in the engines is derived at by formula from the FAA, not by actual requirement.
So anything we do to make the box smaller lets us breath less and thus less oil vapor goes out the breather. This why some engines like it at 6 and others at 5 or even 7. The blow by varies with each engine and thus the size of the box required to handle that blow by varies with each engine and thus that is why one fella?s engine may run at 7 fine but another blows oil until 6 is reached. His engine and installation just wants a bigger box to deal with his natural crankcase pressure.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at you own risk."

Thanks!

Mahlon, thanks for the great explanation!

I'm pretty sure I have the smaller breather fitting on my IO-360-A1B6. I don't remember the exact dimension of it, but it's 5/8" instead of 3/4" or something like that. I wonder if that also contributes to raising the pressure inside the case. Do you think upping to the larger breather fitting would help lower the pressure?

The reason I ask is because I have compression of 76/77/77/76, the engine is otherwise running great. I have no air-oil separator, and I kinda would rather not have one. I get film/haze on my RV-7's belly pretty much regardless of oil level. Oil consumption seems almost entirely composed of breathed-out oil.

FWIW, my strategy for adding oil is exactly what Gary Sobek outlined below. On average I'm running 5.5 quarts.

I would love to reduce my breathed-out oil without installing a separator.

)_( Dan
RV-7 N714D
http://www.rvproject.com

I add 8 with a new filter at oil changes. It winds up at 7 once the engine is run up to fill the new filter. I add a qt at the 6 qt level, usually around 20 hrs, then I change at about 30 hrs again. New Lycoming 0-360 A1A. I broke in with Aeroshell Oil 80 for 50 hrs (changed oil at 1 hr, 25 hrs, and 50 hrs, each time with a new filter) then switched to Aeroshell 15W50.

Roberta

Hi ya'll,

I've considered adding a separator at some point in the future (I'm not thrilled with the 'burn it on the exhaust and then throw it on the belly' approach). However, I'd only be willing to do this if I was collecting the waste gunk in a small container rather than throwing it back into the engine.

Does using a separator decrease the amount of oil one needs to add between changes if you aren't dumping the return oil back into the engine?

I'm also real curious about Dan's question on larger breather ports.

This is an interesting topic.

Oil seperator

Kevinh:
The oil that is colected or returned to the engine from a well built seperator is just as clean as the oil that you put in the engine.
Doyle Reed Casper two

The volume of air will not normally affect the pressure but a smaller volume will not absorb the pulses of blow-by gas as well as a larger volume. So when the oil level is high the pulsation could be quite violent and agitate the oil surface, sending drops out the breather.

Of course this is only theory so I have no idea if it really happens.

Conor
RV-9A 90990 wings/fuselage

Not So Fast!

I can believe Conor's explanation, Mahlon's no.

Flow in equals flow out, and the internal volume doesn't affect that. It will stabilize pressurize in more or less time depending on volume (think compressor tank size). The only pilot controlled variable is power which affects input volume thence crankcase pressure as gases squeeze out the breather which is fixed. Another analogy: pouring water at some fixed rate into two different sized buckets. Once each is full, what pours in pours out at the same rate, but the larger bucket takes longer to overflow. Compressiblity of a gas isn't part of the issue, and crankcase pressures are low, anyway.

You have any empirical evidence for your explanation, Mahlon? Without such, I suspect engines use more oil if more is available to froth and vaporize, however they go about it, then toss it overboard.

Bart told me to run 5 quarts to minimize oil use. Also said that Aerosport sees many more engines not make it to TBO when they use less oil, like 25hr/qt, vs. 8-12hr/qt.

John Siebold

casper said:

The oil that is colected or returned to the engine from a well built seperator is just as clean as the oil that you put in the engine.

Click to expand...

Que? I've heard stories about the oil in the return line being a nasty mix of acid, water, oil and evil fairy dust. Anyone have anything else to add on this point? - I've never had a plane with a separator before.

Also: Anyone have anything to add about the idea of using a larger vent line/fitting in hopes of decreasing the velocity of the air out of the engine?

John, The way it was explained to me, is that the physical volume of space the inside of the engine, absolutely makes a difference, relative to the amount of blow by produced by the engine. Lets say the engine makes 2 quarts of air per hour from its blow by and the breather can vent 2 quarts of air per hour. Everything is equal and no pressure build up. no oil vapors being forced out the breather. Now, lets say the inside of the engine has 2 quarts of volume of extra space and the engine makes 2.1 quarts of blow by per hour. As the engine runs we will still have a zero pressure build up, until that extra 2 quarts of space inside the engine is used up by the extra .1 quart of blow per hour being produced. Until we use up the extra volume of space in the engine, we have no pressure build up, but at some point depending on how long the engine runs and how much extra blow by beyond outlet capacity we produce, we will eventually, in theory, start to build up more internal crankcase pressure at the rate of .1 quarts per hour. We may never get to the point, that we equalize the extra blow by volume and the extra space volume, in the engine, to cause the pressure build up inside the crankcase.
Now let say, the extra volume in the engine was only .1 quart worth of space and everything else was constant. We would get to a point that we would start to build crankcase air pressure, a lot faster then with a inside volume of greater size. This increased crankcase air pressure would start to force oil vapors out the breather.
Now lets say, the inside volume of the engine was 50 quarts and not the two quarts of space we used in the first example, or the .1 quart of space we used in the second and we keep the supply and the vent capabilities the same. It would make the pressure build up a much harder thing to achieve, because it might take forever to use up that extra space provided by the increased volume inside the engine before we started to make crankcase pressure high enough to force the oil vapors out the breather.
This is how it was explained to me and frankly I never challenged it. It seemed to make sense that it would happen that way..could be wrong but it seems to work that way during engine operation. .If we have an engine that breaths very little oil or no oil at a 7 quart oil level at 2400 rpm for 1000 hours of engine use, but as life goes on, starts to have increased blow- by, from ring wear, we will start to see it blow oil out the breather at a more rapid rate, at the same power settings and rpm settings. When this happens, if you lower the oil level, in the engine, you stop the breathing temporarily until the amount of blow by increases some more and then you start breathing it on the belly again. So it really seems that the inside volume of space, in side the engine, does effect how much you breath rather then how much oil is there to slosh around. If you restrict the breather outlet sufficiently, it will cause more oil on the belly, at the same rpm setting. If you increase the blow by of the engine, it will put more oil on the belly at the same RPM setting and if you put more oil into the engine it will breath heavier at the same rpm setting. So the constants, that seem to effect how much oil you breath onto the belly, are volume in, volume out and size of the inside of the engine, not the rpm that is sloshing the oil into the air. That is not to say that if we also put way more oil in the engine than we should, that the extra oil we are sloshing around would also cause it to breath more heavily, due to, the increased vapor, that that extra oil caused, because it would. But which has a more direct effect on the amount we breathe out, I don't know for sure. So I don't really know for sure why lowering the oil level makes it breath less, less oil to slosh around or less pressure to push those vapors out, I just went with what I was taught because it seemed to make sense to me.

Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at you own risk."

Hmmmmm..

First engineering principle: nothing is ever simple.

Mahlon, I'm still squirming over the volume vs. pressure build-up concept because the change would be very small. A quart is small compared to the total volume inside the engine. Blow-by is small volume. The change in oil overboard is small. All compared within a span time which is a large number. So on and so on... The idea of intensified pressure pulses on a larger pool within a smaller volume is interesting.

After 36 years of slicking up bellies, I'll simply accept keeping the oil level low. It would take some careful instrumentation and rigor to pin this issue down, but I've got better things to. Besides, don't expect me to figure it out. My class managed to stop up the sewage treatment plant on top of the engineering building; upset a bunch of profs.

John Siebold

Dan: Fluids do not compress...lower oil levels allow space to be occupied by gas...which does compress....???? Perhaps the full oil situation doesn't allow for increased pressure from heat...thus oil blow out...Just a guess on my part...not an expert.

Engines that use less oil don't make it to TBO?

RV7ator said:

Bart told me to run 5 quarts to minimize oil use. Also said that Aerosport sees many more engines not make it to TBO when they use less oil, like 25hr/qt, vs. 8-12hr/qt.

John Siebold

Click to expand...

John, am I reading you correctly that Bart told you engines which use less oil are less likely to make it to TBO than engines that use more oil? Trying to figure out why this would be true...

--Mark Navratil
Cedar Rapids, Iowa
RV-8A N2D flying 15.8 hours

What is normal?

czechsix said:

RV7ator said:

Bart told me to run 5 quarts to minimize oil use. Also said that Aerosport sees many more engines not make it to TBO when they use less oil, like 25hr/qt, vs. 8-12hr/qt.

John Siebold

Click to expand...

John, am I reading you correctly that Bart told you engines which use less oil are less likely to make it to TBO than engines that use more oil? Trying to figure out why this would be true...

--Mark Navratil Cedar Rapids, Iowa RV-8A N2D flying 15.8 hours

Click to expand...

Mark I am just echoing your post. Lycoming can clear this up possibly. There is a reasonable value of oil use. I find a healthy Lyc uses 1 qt ever 16/18 hours.

25hr/qt is out standing and not sure many are getting that much or if that indicates a problem. What is the problem? I have hear of high oil consumption but low use complaints I have not heard as a common problem.

(remindes me of a joke about old British motor cycles or sport cars: "If it ain't leaking oil it does not have any oil in it.")

12hr/qt is not bad and typical of a mid higher time engine; 8hr/qt is getting to be too low and it is burning a little extra (thru rings/valves) blowing it out the breather from too much blow by. Lets assume no massive oil leaks anywhere.

Where does oil go normally. Its going out the exhaust or breather as discussed. If it is going out the exhaust it is being burned. If the rings are worn or the valve guides are worn, than more oil can make it into the combustion chamber. If the rings are worn, than it contributes to more blow-by, which gets more air into the crankcase. This is where the breather comes in. Even at lower oil levels if the piston is squeezing out excessive blasts of gas/oil into the crank case, more will go out the breather, regardless of oil level. That is what the breather is for anyway, to evacuate the blow by out the crank case. Of not you would blow the fwd crank seal out.

I guess if the oil ring on the piston was scraping too much oil off the cylinder walls this would add wear. That would imply an improperly built engine. If the engine is properly built and broken in this should not be a problem.

However we are going on the assumption that some oil use is Good-ness? Car engines have low oil use, but they are designed like that. With an air cooled engine you need more clearance, so you get more blow-by, more oil past the valve stem guides, which as mentioned gets burned or blown out. So by design Lycomings are designed to use oil. If the oil use is too low that may mean oil is not getting where it needs.

Something does not add up. Why would low oil use not be good? I guess if there was real low use, I would investigate or suspect my buddies adding oil to my engine with out telling me, as a joke.

George