Menu Sign In Contact FAQ
Welcome to our forums

Oil analysis - large variations

Since I started sampling in 2005, I have seen aluminium values from 1.7ppm to 13ppm.

This runs right through a "rebuild to new limits" in 2008, with the big variations seen before that and after that.

The other metals are less affected, with e.g. iron varying from 11ppm to 44ppm.

Iron and chromium have been much lower after I started using Camguard.

I wonder if there is some factor which heavily influences which metals drain out with the oil. The engine is always run before the oil is drained but I wonder if perhaps there is some highly critical factor e.g. how warm it is allowed to get.

Shoreham EGKA, United Kingdom

I had aluminum in the oil this year - and some in the oil filter - but it looks like it came from a broken starter adapter in 2012. This assumption seems to be correct, because the last two oil changes it was less and less, and last week there were no aluminum particles anymore and very little in the analysis.

I use AeroShell 15/50 and i think i read somewhere that this oil contains everything Camguard does ...? But maybe i am not right

My 0-320 over the last four years:
Aluminium = 8, 5, 5, 3.
Iron = 26, 29, 21, 15.

My Copper is high 31, 43, 28, 31. Blackstone's say: We mentioned before how the copper is from the use of A/S 15W/50 and therefore isn't a problem. As long as it stays steady, we'll probably unhighlight it next time. The other wear metals are low and steady, which is what you expect to see from an engine that's running normally. No fuel or moisture was present and the air and oil filters kept silicon and insolubles under control. Even the viscosity is perfect for 15W/50. Don't change a thing. This engine is ready for the winter months.

United Kingdom

Can you read anything from a one-time test, or is it only indicative if measured over time? In other words, will an oil test when looking to buy a plane tell you anything at all?

sorry for posting another question, rather than contributing to the original one...


It will still be useful in that if the values are outrageously high, that's a big warning unless there is a really good explanation e.g. a recent overhaul, or the engine been sitting around without being run (in which case you ought to factor an overhaul into the purchase price anyway).

But you also need (if it's a prebuy) to open up the oil filter. The seller should not object; they are cheap and quick to replace. Larger particles end up in the filter or the bottom strainer, while general engine wear ends up in the oil analysis.

OTOH a very recent filter, or a very recent oil, won't tell you anything useful. It needs to have say 20hrs+ on it.

Shoreham EGKA, United Kingdom

Here are links to two magazines containing articles on oil written by Mike Busch who owns and runs Savvy Maintenance who provide maintenance management services for GA aircraft:

Well worth a read.


We have never done any tests to see if how warm the oil gets is a factor in how much metal shows up, so I can't say for sure. But my instinct is no. The oil does a pretty good job of holding everything in suspension, and that's true whether the oil is hot or cold. Cold samples will sometimes show traces of moisture and/or fuel, since those contaminants don't cook out if the oil doesn't get up to operating temp before sampling.

I think operational factors are going to have more of an effect on how much metal shows up in analysis. But even more than that, you might be seeing aluminum from the case itself. Any time the engine sits idle you can get moisture that collects on the case, and that causes oxidation. The oxidized aluminum washes into the oil when you start the engine, and voila! Extra aluminum. It might be worth looking at your aluminum values vs. hours on the oil and the time it took to accrue those hours. We consider anything less than 5 hours a month to be inactive, though of course that will vary depending on climate.

Someone else mentioned the filter, and that is indeed a good thing to check. Anything you can see in the filter is going to be too large for a spectrometer to read, so that's another useful tool for determining engine condition.

As far as what you can tell from a one-time sample: trends are very helpful in determining whether the engine is in good shape, but we can also sometimes spot problems on the first sample when wear is excessively high compared to averages. Often, in engines that are up for sale, it's just a matter of corrosion, but oil analysis labs can't tell the difference between metal that's from corrosion and metal that's from a problem, so any excessive wear should always be checked out.

That's really interesting... I recall reading a lot of stuff in the usual aviation places that one should take a lot of care with when the sample is taken, measured as say 1 minute after starting to drain the oil, etc.

Normally one runs the engine at least for a few minutes anyway, to warm it up so the oil drains out easily.

Also if one is not allowed to work in the hangar and has to do it outdoors (like me) having a warm engine is handy for putting your fingers between the cylinders, in the winter

Shoreham EGKA, United Kingdom

Here comes another one. Same oil sample sent to both labs.



Notice that iron and aluminium have gone in completely different directions between the two labs. This means that the usual explanation (“different equipment calibration”) cannot be right.

Same for copper.

I am going to send these results to both labs for their comments.

I also notice that Avlab have removed their long term averages for that engine type and replaced them with N/A. I wonder why.

Last Edited by Peter at 06 Feb 13:38
Shoreham EGKA, United Kingdom

I think that it is critical to always use the same Lab. It looks like different labs always come up with slightly different results, and probably a TREND can be seen better when the same lab is always used. I remember reading on COPA that different labs come up with different results. I do not know WHY this is so …

Last Edited by Flyer59 at 06 Feb 14:55
66 Posts
Sign in to add your message

Back to Top