Oil analysis: slightly elevated aluminum for years

denverpilot

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

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...
 
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.
 
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)
 
The 470 has a steel or stainless steel dipstick. Lycomings use aluminum.
 
Thanks Dan. I didn't know and was only going by the OP's last sentence...well, the sentence before last.
 
The 470 has a steel or stainless steel dipstick. Lycomings use aluminum.

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.
 
How do your oil filter cuts look?

How are your CHTs a oil temp and pressure?

How's hour performance vs book numbers?
 
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.

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.
 
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.

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

Generally.
 
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