Thoughts on After Engine Shutdown

Discussion in 'Maintenance Bay' started by Cruzinchris, Jan 11, 2019.

  1. Cruzinchris

    Cruzinchris Pre-Flight

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    After flying, I have opened the oil filler and observed smoke coming out. Is this just hot oil vapor or possibly water vapor? Would it be advisable to always let this vapor vent after flying? It last about 5 minutes on a 320 Lyc that burns no oil.

    On another front. Should one consider putting a rubber ball in the exhaust pipe to block raw air from getting in the engine? If the engine stopped with an exhaust valve open then atmospheric air with plenty of water vapor could enter the cylinder. Same thought with the breather hose.
     
  2. Checkout_my_Six

    Checkout_my_Six Final Approach

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    one of your exhaust valves is always open.....Na, I wouldn't worry bout it.

    letting the moisture out is fine while the oil is hot.....
     
  3. Ryanb

    Ryanb Final Approach PoA Supporter

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    It’s just vapor from the hot crankcase. Unless you’re seeing milky residue or anything abnormal around the filler tube, than there shouldn’t be anything to worry about.
     
  4. Dan Thomas

    Dan Thomas Final Approach

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    Milky residue is oil/water emulsion and is readily noted after flight on cold days, especially short flights. The filler tube, depending on length and location, can stay pretty cold and you'l get condensation in there.
     
  5. Unit74

    Unit74 Final Approach

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    I pop my oil filler every time. It's water vapor, or at least that is what I was told. Totally normal.
     
  6. Stewartb

    Stewartb Final Approach

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    I've never seen any data to support pulling the dipstick to vent moisture. I like paths into my crankcase to remail closed as my flying environment is gravel and dusty, including parking.

    Flying often manages corrosion better than anything.
     
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  7. Capt. Geoffrey Thorpe

    Capt. Geoffrey Thorpe Touchdown! Greaser! PoA Supporter

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    The byproducts of combustion, in an ideal world, are CO2 and water. In the real world, there is some sulfur and lead in the fuel, plus you get unburned hydrocarbons, carbon monoxide and oxides of nitrogen. A lot of that finds it's way past the rings and into the crankcase. Your car has a positive crankcase ventilation system that helps clean that garbage out of the oil - your aircraft engine does not - so the contents of the crankcase are pretty much blow by which has a water concentration something like 15% (operating from memory - could be wrong with that number - but it's way more water than air can hold at normal ambient temperatures). So, letting water out is a good thing. Sealing up the engine to prevent water from getting in (unless we are talking about long term storage) would be counter-productive.
     
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  8. Salty

    Salty En-Route PoA Supporter

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    If air comes out, air has to go back in inevitably. I guess that air might be a bit less humid, but I’d wager swapping out a tiny bit of air with air less humid is going to make less difference than you could measure.
     
  9. 455 Bravo Uniform

    455 Bravo Uniform Pattern Altitude PoA Supporter

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    I do it just cuz I don’t want any of that stuff to condense back into the oil/crankcase. The crankcase is vented anyway, right? So other than opening up more of the crankcase as a breezeway by doing that, it’s not like it’s totally sealed anyway.
     
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  10. Capt. Geoffrey Thorpe

    Capt. Geoffrey Thorpe Touchdown! Greaser! PoA Supporter

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    Typically less than 1/10 as humid.
    The blow-by in the crankcase is about 13% water vapor. At 70 degrees 100% humidity, you have about 1.5% water vapor.
    As your engine cools down, all that extra water condenses.
     
  11. Mooney Fan

    Mooney Fan Line Up and Wait

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    I have always opened my dipstick after a flight to release the condensation. That moisture will turn to liquid. More that I let out seems the less I have to burn at 180 operating temp
     
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  12. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    This! I vent my oil filler after every flight, and in fact I leave it that way until I'm checking oil for the next flight, though in the winter with the cowl door mostly closed, just open enough to run the extension cord for my heater in there, and a blanket over the top.

    I'm in a hangar where I've never seen a bug or a bird, so I'm not really worried about things getting in there. If I were, or if I were in @Stewartb's situation, I would put a different cap on, with a dehumidifier hooked up to it like another PoAer recently built.
     
  13. Timbeck2

    Timbeck2 Final Approach

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    I open my oil filler tube after every flight and leave it off until I finish the after flight wipe down/bug removal and cover installation then I reinstall it. It may or may not be helping remove some water vapor but I think everything helps.
     
  14. Dan Thomas

    Dan Thomas Final Approach

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    Not with most engines. When vapor comes out the filler, drier air is going into the crankcase breather. The heat of the air in the crankcase drives the exchange and it will continue until it reaches equilibrium with the ambient air. Only in some small Continentals with the kidney tank and the filler neck attached far down the tank will that not work; the oil closes off the escape.
     
  15. Salty

    Salty En-Route PoA Supporter

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    I don’t think so. The warm air is going to rise from both the breather and filler. I don’t see what would drive a circulation like you describe.
     
  16. Stewartb

    Stewartb Final Approach

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    Breather lines exit the top of the engine and are routed to below the bottom of the engine. They aren't going to breathe anything unless it's pressurized. On a Continental the breather outlet is up front and the line slopes up as it traverses the engine, then turns down. If condensation in the line is a concern? Insulate the line from outlet to where it turns down. Common practice in the north. Not an issue with the typical Lycoming that has the breather outlet at the rear.
     
  17. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    There are certainly some engines - mine is one - where this won't work. Mine won't work because my breather tube is attached not to the engine itself, but to the oil filler tube, right below the cap. Doesn't matter how hot the engine is, it's not going to develop circulation through the breather. That's part of why I leave it open: aside from the flow that appears to happen right away (visualize turning a test tube filled with water upside down), I'm mostly dependent on diffusion to eliminate the water from the crankcase.

    It doesn't take much of a differential to make air move three feet vertically. With a hot engine, venting the filler cap gives the warm air inside the engine the opportunity to go where it wants (up), and air will easily be pulled through the breather to replace it. Just not in instances like mine, where the setup is different and the breather and filler are attached together.
     
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  18. Stewartb

    Stewartb Final Approach

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    Test your theory. The hot air in the breather isn't going to give way to cool air given that the breather contents will be higher (warmer) than the oil tube contents. What you see venting out the oil tube is being replaced by air slipping in through the same tube. Plug your breather outlet and see if the venting out the oil tube stops.
     
  19. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    Like I described in the first half of my post, it doesn't work on my plane because the breather is attached right to the top of the oil filler tube, not directly to the engine. So in my case, you're correct - Everything is happening through the filler tube. But, I think with a different configuration and a steadier state, that air will move through the breather too.
     
  20. Stewartb

    Stewartb Final Approach

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    I have a Continental with the front outlet and a Lycoming clone with the rear outlet. What I described is true with both. Venting through the oil filler will be more productive in my Continental than the Lycoming given where the oil fillers are. No matter. Condensation is going to happen to matter what we do with the filler cap.