[Snowflake]

Okay, how about this... Let's say your engine is shaving particles off large enough to see. As part of that particular wear/failure process, wouldn't we expect a *range* of sizes of particles to be removed, from detectable, micron-sized, all the way to visible? Not everything that gets shaved off will come off in visible-sized pieces. And if so, wouldn't the smaller pieces contribute to a change in the proportions of metals found in the oil sample?

 

[Toobuilder]

Oil analysis in engines serves to pre inform the operator of an impending failure. It can also inform the discrete component that is starting to fail. IE. An accessory gear, carbon seal, O- ring, etc. if it’s big enough to be caught in the filter, it’s WAY too late. Even the best filter is just a coarse garbage screen compared to what is studied for an oil burn analysis.

 

[DanH]

Let's say your engine is shaving particles off large enough to see. As part of that particular wear/failure process, wouldn't we expect a *range* of sizes of particles to be removed, from detectable, micron-sized, all the way to visible?

Yes.

And if so, wouldn't the smaller pieces contribute to a change in the proportions of metals found in the oil sample?

Yes. It should show any significant change for elements soluble in diluent, dissolved with acid, or delivered to the plasma as particles <10 µm, ballpark.

No one is sayin' ICP spectroscopy is without value. However, it has been built up in our community as an omnipotent "tell all". It's not so. In reality it has limitations, and they are useful to understand.

 

[planenutz]

No one is sayin' ICP spectroscopy is without value. However, it has been built up in our community as an omnipotent "tell all". It's not so. In reality it has limitations, and they are useful to understand.

100% Dan. Well said.

As I tell my customers - it is just one tool in the toolbox and it can assist in some circumstances, but its important to remember the other tools are also there to be used.

 

[planenutz]

Okay, how about this... Let's say your engine is shaving particles off large enough to see. As part of that particular wear/failure process, wouldn't we expect a *range* of sizes of particles to be removed, from detectable, micron-sized, all the way to visible? Not everything that gets shaved off will come off in visible-sized pieces. And if so, wouldn't the smaller pieces contribute to a change in the proportions of metals found in the oil sample?

As Dan said, yes... however let's consider for a minute that the metal in the filter is in the form of quite large flakes... say, 1/8th" diameter. The SOA results might show a slight elevation of iron and chrome, but how valuable is this information to you at this point? Not much help at all really because you are no longer trend monitoring, you are reacting. I would suggest it would be better to carry out an SEM analysis of the particles and determine exactly which material has been recovered, then use the metal map to determine where this material is employed within the engine.

 

[BillL]

Okay, how about this... Let's say your engine is shaving particles off large enough to see. As part of that particular wear/failure process, wouldn't we expect a *range* of sizes of particles to be removed, from detectable, micron-sized, all the way to visible? Not everything that gets shaved off will come off in visible-sized pieces. And if so, wouldn't the smaller pieces contribute to a change in the proportions of metals found in the oil sample?

Maybe. Let's say you had some corrosion on the cam followers- - immediately after that some of the particles likely went into the filter, and as it gets repolished, the SOA might show some increase in iron. Then the degradation continues. Now -the pieces spalled off will be larger, get entrained in the high speed vortex of the crank rotation, some fall on the cylinder walls, but most just get washed into the sump. As the hydrodynamic film has deteriorated (with a porous contact area), some wear (as opposed to spalling) will begin from metal-metal contact and generate (smaller) particles where some will not not sink to in the sump, but remain suspended/entrained in the oil flow- that gets into the filter. As spalling and wear continues, it is not likely (as pointed out) that the SOA alarm will go off.

It would be interesting to quantify the entire progression to failure of a slipper follower from the initial issue.

ChiefPilot - - You stated nicely- - " my engine might be clean inside and not generating debris "- - yep. My filter and SOA got cleaner with hrs and at 250 the SOA is pretty consistent - -I did fly out West a couple of years ago and 10-15 hrs in smoke tainted air. That pushed up my Fe in the SOA and took 2 more oil changes to get in line.

The air must be really clean in Minnesota!! Central Illinois is silica country so with spring and fall winds across corn/beanless fields it is noticeable.

SOA - oil filter inspection and finally suction screen inspection work together to address different failure modes.

DanH is doing a fantastic job of educating us on the details here. If it were charted it's beginning to look like an old oak tree, the leaves are the bits of knowledge.

 

[Snowflake]

As Dan said, yes... however let's consider for a minute that the metal in the filter is in the form of quite large flakes... say, 1/8th" diameter. The SOA results might show a slight elevation of iron and chrome, but how valuable is this information to you at this point? Not much help at all really because you are no longer trend monitoring, you are reacting. I would suggest it would be better to carry out an SEM analysis of the particles and determine exactly which material has been recovered, then use the metal map to determine where this material is employed within the engine.

Yes, I agree, if you're seeing 1/8" flakes in the filter, then you don't need an SOA to know you're in triage mode. But earlier I was getting the impression that people thought SOA wasn't valuable because it wouldn't report the larger particles. While it's true that larger particles won't be measured, there is a progression to consider. Before you get 1/8" particles, you'll get smaller particles, and if you're not to the 1/8" flakes point when you do your oil change, you should see elevated levels that make you wonder what's happening.

It would be interesting to quantify the entire progression to failure of a slipper follower from the initial issue.

I agree. I think that's what labs like Blackstone are trying to do, they do ask a lot of questions about operation conditions, and they do comment on levels that are off the "fleet average" numbers to suggest what could be causing them.

 

[newt]

But earlier I was getting the impression that people thought SOA wasn't valuable because it wouldn't report the larger particles.

I think it's not valuable because we don't do anything useful with the results.

If I cut my filter can open and inspect the pleats and it's full of iron filings, that'll ground the aircraft and see the engine booked in for intrusive maintenance.

If I do SOA and it comes back saying there's a slightly elevated ferrous metal count, I'll go, "Hrm," and keep flying. Next time I change the oil and cut the filter can open and inspect the pleats, I'll pay extra special attention to see if it's full of iron filings. Which I was going to do anyway because that's the normal thing you do even if you don't have a report of elevated ferrous metals, so the SOA result didn't help.

Heavy industry uses oil analysis to tell them what's failing so they can have the right spare parts available on hand next time the machine comes in for maintenance, minimizing revenue-affecting downtime. We don't operate our privately owned recreational vehicles like that.

Has anyone here ever learned anything from an oil analysis that's led directly to a maintenance outcome without evidence in the oil filter? If not, why do it?

- mark

 

[JonJay]

I think it's not valuable because we don't do anything useful with the results.

If I cut my filter can open and inspect the pleats and it's full of iron filings, that'll ground the aircraft and see the engine booked in for intrusive maintenance.

If I do SOA and it comes back saying there's a slightly elevated ferrous metal count, I'll go, "Hrm," and keep flying. Next time I change the oil and cut the filter can open and inspect the pleats, I'll pay extra special attention to see if it's full of iron filings. Which I was going to do anyway because that's the normal thing you do even if you don't have a report of elevated ferrous metals, so the SOA result didn't help.

Heavy industry uses oil analysis to tell them what's failing so they can have the right spare parts available on hand next time the machine comes in for maintenance, minimizing revenue-affecting downtime. We don't operate our privately owned recreational vehicles like that.

Has anyone here ever learned anything from an oil analysis that's led directly to a maintenance outcome without evidence in the oil filter? If not, why do it?

- mark

Way more folks post here about chasing ghosts than discovering an actionable item due to oil analysis findings.