Minimum Oil Level

WDD

WDD

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Vintage Snazzy (so my adult children say)
Learn something new everyday. So this means that my 12 quart of oil max engine should be able to function fine all day on 6 quarts?

No, not advocating taking off with only 6 quarts of oil in your Continental. But maybe 8 or 9.


§ 33.39 Lubrication system.

(a) The lubrication system of the engine must be designed and constructed so that it will function properly in all flight attitudes and atmospheric conditions in which the airplane is expected to operate. In wet sump engines, this requirement must be met when only one-half of the maximum lubricant supply is in the engine.

Here is a nice read I found:

 
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The minimum for my Lycoming in the Lance was 3.5 quarts. It had a 12 quart sump. I never ran it below 9.
 
I’m finding my (new to me) engine doesn’t like 10 quarts. I kept filling it back up to 10, and it kept spitting it out. I now need to find the level it likes. Hope it’s close to 8 or 9 to give me some cushion to the min of 6. We will see.
 
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My io540 likes to be kept between 8&9. Any more than that it just spits out. It actually lists the minimum as two. Every Lycoming I've been around will spit out anything more than 3/4 of its sump capacity.

Mine has marks at 3,6,9,& 12, so it's a bit of a guessing game.
 
My O-290 holds 8, min is 2, anything over 5-6 blows out the breather.. Between 4-5 I add a quart.
 
My O-360-A4M has a max of 8, but anything more than 7 blows out the breather quickly. I fill to 7 and add a quart when it drops to 6. The prior O-320-D2G was the same.

I like to keep the oil at the highest level that doesn't blow out, since it gives peace of mind and with some engines it can run slightly cooler that way.
 
Jim K said:
My io540 likes to be kept between 8&9. Any more than that it just spits out. It actually lists the minimum as two. Every Lycoming I've been around will spit out anything more than 3/4 of its sump capacity.

Mine has marks at 3,6,9,& 12, so it's a bit of a guessing game.
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You are the only one I know who went to extreme measures to test the minimum pilot level required. :)
 
Rgbeard said:
TIO-540-S1AD. I keep it at 9, add oil when it's 8 or below.

I understand minimum-safe is around, or possibly slightly under 3. (I don't have the engine book nearby).
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Yeah, the minimum level for lycomings is surprisingly low. Not that I'm gonna intentionally test it...
 
WDD said:
I’m finding my (new to me) engine doesn’t like 10 quarts. I kept filling it back up to 10, and it kept spitting it out. I now need to find the level it likes.
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Seems to me that you want to tind out the level at which it doesn't spit out, and then keep it between that level and 1qt lower.
 
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My O-320s like 7 quarts (8 is full capacity), and I add a quart when it gets to 6. This has worked well for 35 years.
 
My O-540 holds 12 quarts but the sweet spot is around 6 quarts, the minimum on this engine is 2.75 quarts. Met a guy with the same engine and he insisted it had to have 12 quarts all the time. He said he would add a quart every 2 hours! So if he changed oil every 50 hours, he was adding 25 quarts between changes
 
For those who own a Continental 470, what is the lowest you think it could run at vs the book’s minimum 9 quart?
 
I got mine down to 2 once. The guy that did the oil change got distracted and didn't finish tightening the oil filter.
There are still oil stains on the north end of the airport.

I keep it at 6 and it is happy there. Lycoming 540
 
I'll jump on the bandwagon ...
My Warrior's O-320-D3G will spit out a bit at 7, so I fill to somewhere between 6 and 7 quarts and add a quart when it's a quart down.
If I fill to the 8 quart full sump spec, it immediately spits out a quart and I'll be on my back with paper towels.
 
My AEIO-360 holds 8. AFM says 6 is aerobatic minimum. Anything over 6.5 goes on the belly. So, I keep it between 6 and 6.5.
 
SixPapaCharlie said:
I got mine down to 2 once. The guy that did the oil change got distracted and didn't finish tightening the oil filter.
There are still oil stains on the north end of the airport.

I keep it at 6 and it is happy there. Lycoming 540
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That's why I don't do my own oil changes.

My IO520 behaves at around 11 (of 12 max).
I start with 11 qts and when it gets down to 9 I take it in for the 25 hour oil change. Last time I added oil (2 qts) was when we flew Florida-Alaska-Florida and I pushed the oil change interval to 51 hours. At around 30 hours I added 2 qts to bring it back up to 10.
 
WDD said:
For those who own a Continental 470, what is the lowest you think it could run at vs the book’s minimum 9 quart?
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I can’t say how low you can go in a 470 but mine likes 9 - 9.5 quarts. anymore and it gets spit out. I’ve never had to add anything between oil changes, and I typically go 40 hours between changes. My engine is “newer” with just over 400 hours since new in jan 2020.
 
Garee said:
My O-540 holds 12 quarts but the sweet spot is around 6 quarts, the minimum on this engine is 2.75 quarts. Met a guy with the same engine and he insisted it had to have 12 quarts all the time. He said he would add a quart every 2 hours! So if he changed oil every 50 hours, he was adding 25 quarts between changes
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He is adding a quart every 2 hrs because anything above 10.5 qts in the O-540 gets blown out the crankcase vent. He's just ****ing away oil at $8.33/qt
 
Some people never learn.

A lot of maintenance shops insist on filling an O-320/360 with 8qts at oil change time. I wonder if they do that for liability reasons.

My sweet spot is 6.5 and I add half a quart when it drops below 6.
 
I keep mine at 6, add a quart at 5. Still have minimal blow by- it’s supposed to do that. Just cleaned the belly yesterday. I use a quart every 8-12 hours
 
i have a lycoming o540 which is supposed to hold 12. i keep it at 9, let it drop to just under 7 and then add 2 quarts. it usually take about 16 flight hours to go down to just under 7. anything above 9 ends up on the belly.
 
WDD said:
For those who own a Continental 470, what is the lowest you think it could run at vs the book’s minimum 9 quart?
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I guess it depends on the year because I remember researching this when I bought mine nearly 20 years ago and the answer was 6. I think it was a 1971-O470R
 
@DanThomas

I’m looking to confirm (or deny) a tale told me by an old A&P IA many years ago. According to him, one certification requirement for the engines we fly behind is that the engine must run at full power for “X” minutes after a leak of “y” ounces per hour occurs.

The easy way to satisfy this requirement, should an engine need additional time to pass this test, is to fill a typical O-470 to 12 gallons and let the first 3 gallons blow by as has been discussed here, plus the “y” amount contemplated in the certification requirement. Then the oil drains out at “Y” rate until the oil pump can no longer maintain suction.

If true, this explains why all common GA engines lubricate the belly on purpose at full oil level. The obvious question: is this true? Anybody else hear this Old Mechanics’ Tale? I have never heard this from anywhere else, so I am leaning towards calling it bull****.

-Skip
 
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I find nothing like that. But I'm a Canuck, more familiar with Canadian regulations, so Bell206 might have better advice here.

Anyway, FAR 33 governs the certification of aircraft engines. In the lubrication system section, we see this:

1720820869696.png

Nothing there about oil leakage rates. In https://drs.faa.gov/browse/excelExternalWindow/A443CD7A269CB0A9852565C5005FAD2F.0001 we see the engine certification testing requirements, and I see nothing there either.

Anybody here is welcome to peruse the FARs for themselves if they want confirmation of what might just be another old aviation myth.

The Canadian engine cert regs are here, and are pretty much the same as FAR 33. Even the numbering of the various sections are the same. We're copycats. https://tc.canada.ca/en/corporate-s...ft-engines-canadian-aviation-regulations-cars
 
Skip Miller said:
@DanThomas

I’m looking to confirm (or deny) a tale told me by an old A&P IA many years ago. According to him, one certification requirement for the engines we fly behind is that the engine must run at full power for “X” minutes after a leak of “y” ounces per hour occurs.

The easy way to satisfy this requirement, should an engine need additional time to pass this test, is to fill a typical O-470 to 12 gallons and let the first 3 gallons blow by as has been discussed here, plus the “y” amount contemplated in the certification requirement. Then the oil drains out at “Y” rate until the oil pump can no longer maintain suction.

If true, this explains why all common GA engines lubricate the belly on purpose at full oil level. The obvious question: is this true? Anybody else hear this Old Mechanics’ Tale? I have never heard this from anywhere else, so I am leaning towards calling it bull****.

-Skip
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https://www.flying20club.org/documents/Tcraft_Oil_Usage_09-2014.pdf

Nice back ground on the history of some of this
 
WDD said:
https://www.flying20club.org/documents/Tcraft_Oil_Usage_09-2014.pdf

Nice back ground on the history of some of this
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Yes, but the second paragraph (quoted below) seems to be at odds with what Lycoming is telling us (2 qts minimum in an 8qt sump).

How can you determine by looking at the oil dipstick of a wet-sump engine the minimum oil quantity with which the engine can be operated safely? It is one-half of the maximum indication etched on the dipstick. If the engine holds 12 quarts, for example, it can be operated with a minimum of six.
 
The FARs require the engine to operate safely on half the max oil. Obviously, Lycoming found that requirement to be overkill if they say that 2 quarts is enough.

The FARs are not saying that you HAVE to have the sump at least half-full, just that the engine must be able to operate safely down to at least that level.
 
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