- it appears as though your links relate to automotive engines and oils, as opposed to piston aircraft engines.
No, they really don't. They refer to statements made by the oil producers, among others, regarding oil color and analysis based on color...and it's equally applicable to aircraft or automotive applciations. I'm referring to air cooled reciprocating aircraft engines using formulated aircraft engine oils. The color of engine oil, however, is not a reliable indication in either recip aircraft engines, or automotive engines.
The color of engine oil is certainly an indicator of engine condition -
No, it really isn't. This is a myth. Every oil manufacturer specifically states as much as do each of the engine manufacturers. After more than a few years working on aircraft, I agree. If you want to know what's in that oil, a spectrometric oil analysis is the only way to go. Color tells you nothing. I've seen oil turn black right off the bat, and I've seen oil that scarcely changes color until the next oil change; color means nothing.
Don't take my word for it, though...
The Answer Book - Shell Aviation
Why does oil turn black between oil changes, and why does the time it takes to change colour vary?
When a straight mineral oil turns dark or black, it usually means that the oil is starting to oxidize and needs to be changed. Because mineral oil doesn’t absorb much of the dirt and sludge in your engine, the oil stays clean and the inside of your engine gets dirty. Ashless dispersant oils, on the other hand, are designed to get dirty so that the engine will stay clean. Just how quickly the oil turns black depends on a number of factors, including the condition of the engine, the dirt load, the oil temperature, the normal air/fuel mixture, the type of fuel, the time since the last service, and the frequency and duration of your flights. Basically, the important thing to remember is to change your ashless dispersant oil on calendar and engine time, not according to its color. Also, oil analysis can help ensure that the oil is still in good condition even though it may have turned black.
http://www.exxonmobil.com/lubes/exxo...1_OilColor.pdf
[QUOTE]The color of the oil will change during normal engine operation when additives do their job of protecting the base stock. Such changes do not affect the performance of the oil and do not indicate contamination or other malfunction.
The phenomenon referred to as “Black Oil” is not due to oil discoloration but to the suspension of very small amorphous particles in the oil. When the particles are filtered from the oil,the color reverts to normal. Black oil arises in certain engines due to an artifact of the engine design. It cannot be eliminated by oil development or reformation.
Motor Oil Myths and Facts
The Dark Oil Myth
Dark oil does not indicate the need for an oil change. The way modern detergent motor oil works is that minute particles of soot are suspended in the oil. These minute particles pose no danger to your engine, but they cause the oil to darken. A non-detergent oil would stay clearer than a detergent oil because all the soot would be left on the internal engine parts and would create sludge. If you never changed your oil, eventually the oil would no longer be able to suspend any more particles in the oil and sludge would form. Fortunately, by following the manufacturer's recommended oil change interval, you are changing your oil long before the oil has become saturated. Remember, a good oil should get dirty as it does it's work cleaning out the engine. The dispersant should stop all the gunk from depositing in the oil pan.
The only real way to determine whether oil is truly in need of changing is to have an oil analysis performed. Since most people don't want to bother with this, it's acceptable to err heavily on the safe side and simply follow the manufacturer's recommended change interval for severe service. There are still a few cars that specify 3K intervals for severe service, but not many. If you look at countries other than the U.S., the oil recommended change interval is much higher than even the normal interval specified by vehicle manufacturers in the U.S.
Color of oil isn't a reliable method of determining engine health in automotive or aircraft engines. If anything should be noted with respect to color, it's not the actual color one sees, but two independent factors worth noting in some cases (but not all): rate of color change, and transparency of an oil sample film. It's not uncommon for a rapid change of oil color to occur, and this is not a reliable indication of engine health, but may be a clue to do further investigating...especially if historically this has not occurred with this particular engine. So far as light and oil color of a film sample, this is still subjective and requires spectrometric analysis for any meaningful insight.
This thread primarily concerns oil consumption, not color. Oil consumption is a product of many factors, but the actual rate of consumption is a trifle compared to changes in the rate of consumption. Whether the engine is burning a liter an hour or two or none, it's much more important to look at the history of the engine and note changes.
Is the original poster filling the engine to capacity every time...and subsequently seeing a liter or two blown out the breather? Most piston engines prefer to run a quart or two low, and any extra will quickly be blown overboard. This doesn't indicate an engine health issue, but an operator error issue.
I went to a Shell / Lycoming seminar and was told the way they determine the oil capacity of the sump is to work out the worst possible oil burn for the aircraft endurance then bung a couple more quarts in on top of that, that determines the size of the sump.
That's the method? See how much it needs and "bung a couple more quarts in on top?" It's a little more exacting than that. The certification standards for recip piston engines, to include engines such as the 0-200, are that the sump holds double what the engine actually requires. It's found in the certification regulation 14 CFR 33.39 (Airworthiness Standards, Aircraft Engines), and reads:
§ 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.
Typical maximum oil consumption for a small piston engine is about a quart an hour...which equates to just over a liter. This isn't necessarily a bad thing. If there are concerns, one should be performing inspections and maintenance to determine if further investigation or work is warranted.
Oil consumption increases as oil degrades. Longer times between oil change intervals may see an increase in consumption in some engines.
Teledyne Continental makes the following statement about oil consumption:
Teledyne Continental Motors ||Visitor Services||
Evaluate the overall oil consumption with respect to the engine installation. In general, look for stability of oil consumption rather than level as a health indicator. If you have a highly loaded installation or turbocharged engine, you may want to evaluate and reflect on the oil consumption rate between a multi-viscosity oil and a straight-weight oil. Generally the use of multi viscosity oil will result in a lower oil consumption level. It is not harmful to change the basic type of oil used in the engine and to evaluate the result.
And, of course...
To guide the long-term oil selection and engine monitoring process, I would begin a disciplined oil analysis program. Again, our TCMLINK Aviator Services program provides a convenient and cost effective method for the owner/operator to track his oil analysis results. Followed with discipline, oil analysis can help you monitor engine wear trends somewhat more scientifically as compared to reliance on "hangar talk".
So far as "hangar talk," what you won't find from Shell or Mobil, or Continental or Lycoming...is a reference suggesting you should determine your engine's health using oil color. You'll find a number of references to spectrometric oil analysis, however...which is a little more scientific and accurate than guessing about the engine because you think you know something about the color.
You'll also find that the emphasis isn't on the amount of oil the engine is burning or passing, but on the stability of that rate of consumption. If you're one liter an hour now but it changes to two on the next flight, you may have a problem. Likewise, if it suddenly drops, you may have a problem, such as an occluded breather with an impending shaft seal failure...something along those lines. Change in the rate of consumption is much more important than how much is actually being consumed or lost.
Continental provides the maximum consumption number based on the percentage of power at which the engine has been operating, as .006 X %power, divided by 100. The result is the lbs per brake horsepower per hour, max. You can view the document at:
http://www.tcmlink.com/EngSpecSheetDocs/O200A.doc
Technically it met the Type Certificate Data Sheet but barely (by the way, max oil consumption can be found in this document, available free at FAA: Home)
As far as the TCDS and legal official max oil consumption, re: the TCDS...do you happen to see it there?
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/8f38ff75fb7ad83d8625763500632b82/$FILE/E-252.pdf
No?
...and rings lining up do cause a drop in pressure
A ridiculously outdated myth that wasn't true when people still believed it. It wasn't true long ago, and is not true now, despite the fact that some still cling to this false notion.