Oil analysis: slightly elevated aluminum for years

Discussion in 'Maintenance Bay' started by denverpilot, Nov 28, 2017.

  1. denverpilot

    denverpilot Taxi to Parking

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    So, since the hive mind here has seen things I've never seen...
    And without getting into the silliness of over-analysis due to oil sampling... yeah, yeah... we know...

    Our O-470 has consistently shown slightly elevated aluminum (around 20ppm) for 5+ years.
    So... anyone else ever seen slightly elevated aluminum for years and years on oil analysis? Very consistent.

    For numbers, we've seen as high as 38 (hmm) on one oil change back in 2013, and our "unit average" from Blackstone is 16. Their "universal average" for this type of O-470 is 7. Last time we were at that average was 2011.

    Other maybe pertinent details, maybe not... if you have other questions, ask... If I know, I'll answer.

    - Engine is about 1200 hours. O-470-S.
    - Prop was overhauled quite some time ago. We had some minor "spitting" of oil from it four or five years ago which after following the SB from the manufacturer to "deep cycle" it once in a while, stopped completely.
    - Oil changes run anywhere from 20-35 hours depending on our schedules. Average runs about 25 is the idea. Probably ran closer to 30 the last four years.
    - Chrome cylinders.
    - No appreciable oil burn (Maybe a quart in 30 hours...)
    - Definitely some small oil leaks that haven't been hunted/found, but always a little oil kinda "everywhere". (Blackstone also said this could be case spalling and a leak at the case half seals...)
    - We do run CamGuard but not sure if we were running it in 2012 when this was first seen. Don't think so.
    - AeroShell 15W50.

    Anything else y'all have seen on low-compression big Continentals and aluminum?
    Figured I'd ask. Like I said, Blackstone says nothing they're concerned about.

    "...the high aluminum reading is not inconsistent with past samples, and since all the other
    wear metals look fine, we're not too concerned about aluminum at this point. When aluminum is the only element out of line like this, it often shows something like case fretting or even an aluminum dipstick. Look for oil leaks along the case halves."

    Aluminum dipstick is a possibility... feels lightweight, and it looks shiny... that's about all I know about the stupid thing. LOL. Maybe we play with our dipstick too much? :)
     
  2. denverpilot

    denverpilot Taxi to Parking

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  3. Let'sgoflying!

    Let'sgoflying! Touchdown! Greaser!

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    have heard of case fretting causing this.
    I don't see mention of a screen or filter element inspection?
     
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  4. denverpilot

    denverpilot Taxi to Parking

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    Thanks, forgot it. Filter, and nothing ever found in it... always inspected. So this is all tiny tiny stuff in the oil...

    Then again, aluminum in tiny amounts in filters is hard to see/detect... since it's not ferrous... so I'll say that... but anyway...
     
  5. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    Nate, some case fretting is possible as they noted. Also maybe possible is a piston pin plug. If it were the latter, though, I'd expect it to have bigger chunks and something that would be noticeable in the filter.

    I'd continue not to worry about it. As you've said it's consistent with what it's been doing the past 5 years. The real point of oil analysis is to look for deviations from what the engine normally does.
     
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  6. Timbeck2

    Timbeck2 En-Route

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    Does your dipstick have any divots or noticeable wear? Sometimes the dipstick will vibrate against the side of the hole in which it extends into the case. Mine does. (Lycoming O-320)
     
  7. Dan Thomas

    Dan Thomas En-Route

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    The 470 has a steel or stainless steel dipstick. Lycomings use aluminum.
     
  8. Timbeck2

    Timbeck2 En-Route

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    Thanks Dan. I didn't know and was only going by the OP's last sentence...well, the sentence before last.
     
  9. denverpilot

    denverpilot Taxi to Parking

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    I’m going to take a magnet to it and make sure someone didn’t replace the right one with the wrong one. Thanks for the confirmation.
     
  10. James331

    James331 Touchdown! Greaser!

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    How do your oil filter cuts look?

    How are your CHTs a oil temp and pressure?

    How's hour performance vs book numbers?
     
  11. denverpilot

    denverpilot Taxi to Parking

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    Post 4. Fine.

    Normal CHT on a single cylinder gauge (no engine monitor), oil temp always has been slightly low (gauge suspected) but in the normal range, pressure good.

    Normal “Nothing to write home about” Cessna speeds. LOL.
     
  12. James331

    James331 Touchdown! Greaser!

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    Well shy of a huge spike in that analysis trend, doesn't really sound like an issue in that case.

    A engine monitor would be a good investment however. I'm reluctant to fly IMC or night without one.
     
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  13. Dan Thomas

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    A steel dipstick is a flat band. Aluminum is a round cross-section.

    Generally.
     
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