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Does the ppm of metals in oil analysis depend on the oil level?

Obviously it will depend on how much oil there was in the engine when you sample the oil so e.g. a given amount of copper may be 10ppm if there were 8 quarts of oil and might be 20ppm if there were 4 quarts, especially if there was a recent top-up from the 4 to the 8 which will simply dilute everything.

But what about the general oil level over the 50 hours or whatever?

Lately I have been running the oil at a low level, around 6, whereas normally I run it around 9. And aluminium has gone up, from 23ppm a year ago to 30ppm (both ~50hr samples).

Administrator
Shoreham EGKA, United Kingdom

So based on that, what are you going to do ?

IMHO, that’s the problem with oil analysis: interpreting results to take decisive preventative actions.

Too many variables such as oil level, oil dilution, when the sample was taken, etc., etc., to come to any decisive conclusions.

So when are aluminum levels so high that you would take action and what actions would you take ?

Example: A typical problem with Lycomings is the piston wrist pin caps rubbing on the cylinders. This will produce copious amounts of aluminum. Would you start pulling jugs just based on the aluminum PPM level from your analysis ?

Last Edited by Michael at 31 Aug 08:14
FAA A&P/IA
LFPN

I am not going to do anything, at this level or anywhere near it. But it’s interesting to watch it. A while ago I got a spike in silicon (which comes from soil) and sure enough the alternate air door had a small gap in it. With it came a spike in copper, which was to be expected.

Administrator
Shoreham EGKA, United Kingdom

Out of interest Peter, why are you keeping the oil level low? On both the PA32 and PA235, the book calls for a minimum of 9 qts. Cant remember what I kept the Bonnie at but I think it was also 8 or 9 but stand corrected. I think they have similar power plants to your TB20 although the Bonnie was a continental rather than a Lyco. As I have little interest in the detail of how things work I probably had/have no need to keep it at 9 (I tend to use the POH as my default guide) so I am just intrigued.

Always looking for adventure
Shoreham

It is the overall condition of the oil that is the thing to watch not just the oil spectro analysis, Michael’s example of wrist pin pin plugs ( piston pin plugs ) giving high aluminum levels might not be a reason to start pulling cylinders but chips of aluminum in the oil filter would be, as these chips are so large it is likely that due to them being filtered by the oil filter the oil spectro analysis alone will show the true magnitude of the problem.

Oil analysis is just one tool in the box of engine condition monitoring.

I have seen people change the oil ( and not record this ) just before a buyer gets an aircraft inspected prior to purchase, the analysis comes back clean but this usually hides a multitude of problems in the engine as the analysis is based on the assumption that the oil has run about 50 hours in the engine with only normal oil consumption.

why are you keeping the oil level low?

It is still in spec – see here

And anything above about 10 is lost from the breather.

Oil analysis is just one tool in the box of engine condition monitoring.

Sure. The filter and the strainer will pick up larger pieces but they are clean.

I have seen people change the oil ( and not record this ) just before a buyer gets an aircraft inspected prior to purchase, the analysis comes back clean but this usually hides a multitude of problems in the engine as the analysis is based on the assumption that the oil has run about 50 hours in the engine with only normal oil consumption.

Based on what I have seen I think this may be quite common in for-sale aircraft, but I don’t mean necessarily covertly. Also if you are buying a low-time plane, say a hangar queen with 2hrs in the past year, and the oil+filter has been changed every year, there is no point in checking them.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

I am not going to do anything, at this level or anywhere near it.

Precisely and that’s why I consider oil analysis just one tick above being completely useless.

The scenario is almost always the same: you perform an oil change, the results come back a few days later, such & such levels are up, but you just finished the 25h, 50h or whatever inspection routine and hopefully you’ve checked the oil filter contents. With nothing in the filter and no other anamolies found, you soldier on wondering what’s causing the high(er] levels of [whatever] …

FAA A&P/IA
LFPN

I was reviewing the Lycoming Service Instruction 1492D pertaing to piston pin cap wear and thought I would copy the part about Oil Analysis.

The take-away here is simple: if alminum goes up – check your oil filter for junk ! Oh yeah, you should be checking your filter anyways …

Last Edited by Michael at 06 Sep 08:30
FAA A&P/IA
LFPN

I would say no sh1t Sherlock

It goes without saying that if your metals keep rising then there must be a reason. And people should be looking in the oil filter (and on Lycos the strainer too) anyway.

So while oil analysis itself doesn’t tell you much, it tells you what to do next. Unnervingly close to a PSA test actually….

Administrator
Shoreham EGKA, United Kingdom

So what good is it then ?

I mean the decison tree is so bloody simple :

Change oil – take sample & open filter

Nothing in filter = keep flying
Nothing in analysis = keep flying
Something in filter = stop flying
Something in analysis = see filter

FAA A&P/IA
LFPN
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