Oil Filter Test vs. Oil Analysis Results

[ChiefPilot]

So as not to derail the other thread, here's a situation I can't quite resolve.

The reusable oil filters performed much worse on the test than did the traditional aircraft filters, which in turn performed slightly worse than an automotive flavor. That they did so is fact and not in question. No debate there in the test data. Comparing 200 hours of oil analysis from my engine with a Tempest 48110-2 filter to the subsequent 200 hours of oil analysis with a reusable filter, however, shows little change - in fact, it's arguably slightly *better* in a couple of the specific elements (silicon). Obviously the oil analysis does not indicate the size category of the particulates, but I am surprised by the conflict between the two data sets.

My first thought is that my engine is just not in a state where it produces enough junk to matter either way, and/or that operating conditions are such that the difference isn't measurable or are happenstance. The slightly better SI numbers in the oil analysis post filter change could simply be the difference in operating conditions, possibly. I'm due for an oil change and am thinking about swapping in a KN HP1002 for 50 hours to see what (if any) effect that has. If my above hypothesis is not wrong, there would be little change in the subsequent oil analysis.

There are other possibilities though. Any and all insights and speculations on why this is are welcome. But save the cheap shots about "dirt don't hurt" or "would you pour some ASTM test dust into your engine" for the other thread please. I'm really interested in being able to understand, explain, and most importantly validate the discrepancy.

 

[Bavafa]

This is exactly the situation for me and the question that I have had, although I don't have as many hours on the existing engine but my last plane which I still have access to and help with its maintenance has just about the same number of hours and the oil analysis show of no increased junk. Of course, I stay very close to the recommended calendar interval of 4 months (typically 5 months or so) and as a result has yet ever hit the 50 hour mark for an oil change. That might be one of the reason to explain the situation.
Furthermore, with the reusable oil filter essentially being free, there is no reason not to inspect and clean it more often in between oil changes.

 

[Auburntsts]

I think the issue is one of correlation. Even though the reusable filters on the whole perform worse than the others in a test environment, in the real world it may take significant time for conditions to develop for the difference in performance to be observed. The question is over time is the performance reduction in these filters going to contribute to premature wear and corresponding issues compared to the other filters? As the man once said, ya pays your moneys and takes your chances. YMMV.....

 

[swjohnsey]

I'm with you. I don't think your engine is making enough junk to make any difference. On my oil analysis wear metals are 2-21 parts per million. The biggest contaminant is lead which comes from fuel. When I change oil at 50 hours it is black. When I cut and wash
my filter (either K&N HP1002 or Wix 51348HP they are nearly pristine. The little junk I wash out doesn't appear to be metal. It is not magnetic. Looks like carbon to me.

 

[bjdecker]

Oil analysis is looking for things measured in the 100's of pM (pico-meters) to nM (nano-meters), vs Oil filters which are trying to catch&contain things that measure in the 10s of uM (micrometer) and larger.

Oil filters are like chain link fences, and the trash they're designed to catch measures in the ping pong ball to softball size. Oil analysis is looking at BB's.

 

[ChiefPilot]

Oil analysis is looking for things measured in the 100's of pM (pico-meters) to nM (nano-meters), vs Oil filters which are trying to catch&contain things that measure in the 10s of uM (micrometer) and larger.

Oil filters are like chain link fences, and the trash they're designed to catch measures in the ping pong ball to softball size. Oil analysis is looking at BB's.

I don't believe this is correct, at least not for the LabOne oil analysis which counts particles in sizes varying from 4 to 70 microns. Actual counts are provided if you pay for their "enhanced" oil analysis package. Other oil analysis might be different; I've only ever used LabOne.

 

[DanH]

Obviously the oil analysis does not indicate the size category of the particulates, but I am surprised by the conflict between the two data sets.

It's a good question Brad. Could post an oil analysis or two, before and after? And do you maintain an air filter?

I suspect typical operating conditions have a lot to do with the results. Pete too. The Twin Cities probably isn't a region with a lot of airborne silicon >4 µm, the range where a good filter, a bad filter, or no filter would make a difference.

Local conditions are a big deal. https://www.sciencedirect.com/science/article/abs/pii/0043164891902794

 

[ChiefPilot]

It's a good question Brad. Could post an oil analysis or two, before and after? And do you maintain an air filter?

I suspect typical operating conditions have a lot to do with the results. Pete too. The Twin Cities probably isn't a region with a lot of airborne silicon >4 µm, the range where a good filter, a bad filter, or no filter would make a difference.

Local conditions are a big deal. https://www.sciencedirect.com/science/article/abs/pii/0043164891902794

Sure. The last four results are attached (I don't have history beyond that handy - away from home - but they're all pretty similar). The most recent three are with the K&P Engineering reusable filter; the one dated 4/29/22 is on a Tempest 48110-2. The hour screw up showing 1212 on the 9/13 sample was my sloppy hand writing down the value in the slip that gets sent it; actual time was 1262.something.



I use the Van's standard K&N 3450 air filter which gets cleaned/serviced as described by K&N each annual. Or replaced, as it ages and gets smaller.

 

[DanH]

I don't believe this is correct, at least not for the LabOne oil analysis which counts particles in sizes varying from 4 to 70 microns. Actual counts are provided if you pay for their "enhanced" oil analysis package. Other oil analysis might be different; I've only ever used LabOne.

Do you have those counts?

 

[ChiefPilot]

Do you have those counts?

No, they aren't included in their basic aviation kit. Getting the actual counts (vs PPM) costs extra and prior to the whole recent discussion it didn't seem like anything I was interested in paying extra for.

 

[Bavafa]

Here is my oil report if this is of any help. The one dated 2/20 is with the Challenger reusable oil filter and the others are Champion.

 

[toolmanmike]

Guys, it was my understanding that it was “recommended “ to change the oil more often with a washable filter? Is that not the case? Seems like most are changing every 50hrs regardless. I’m curious because cost, wise that had previously pushed me to a spin on type filter.
I thought 25 hrs for washable and 50 for “standard” spin on disposables. I’m following these discussions closely.

 

[Bavafa]

Guys, it was my understanding that it was “recommended “ to change the oil more often with a washable filter? Is that not the case? Seems like most are changing every 50hrs regardless. I’m curious because cost, wise that had previously pushed me to a spin on type filter.
I thought 25 hrs for washable and 50 for “standard” spin on disposables. I’m following these discussions closely.

That is the first I hear of this. I have been following Lycoming recommendation of 50 hours or 4 months which ever comes first. Since I don't fly 50 hours in 4 months, I have been practicing the 4+ months interval which typically is about 30 hours or so for each oil change. Lycoming says if you fly often, you can extend that 4 months some

 

[bjdecker]

I don't believe this is correct, at least not for the LabOne oil analysis which counts particles in sizes varying from 4 to 70 microns. Actual counts are provided if you pay for their "enhanced" oil analysis package. Other oil analysis might be different; I've only ever used LabOne.

The Oil results that I've seen from Blackstone, AvLabs report out certain elemental metal counts as "parts per million" -- what isn't clear is what they're actually counting (numerator) against what the solution is (denominator), or what the mechanism to count/measure (assuming Gas or Ion Chromatography).

In any case, it's just simple math...

For reference --

pM (Pico Meter), 10^-12 Meter
nM (Nano Meter), 10^-9 Meter
uM (Micro Meter/Micron), 10^-6 Meter
mM (milli Meter), 10^-3 Meter
cM (centi Meter), 10^-2 Meter
dM (deci Meter), 10^-1 Meter

an Iron(Fe) Atom is 126pM (or .126nM, .000126uM) in diameter.

Doing the math -- Iron(Fe) atom is .000126uM going up against a filter medium that has "holes" 20uM in size, you could push a chunk of Iron(Fe) of ~158K atoms. Ergo - a 20uM filter won't catch anything of significance (...not 100% true, some atoms will be jammed in between the cellulose fibers...somewhere...).

Hence my comment about chain link fence and a BB...I was just off a bit in scale; more like a chain link fence and a grain of sand.

 

[RV6_flyer]

That is the first I hear of this. I have been following Lycoming recommendation of 50 hours or 4 months which ever comes first. Since I don't fly 50 hours in 4 months, I have been practicing the 4+ months interval which typically is about 30 hours or so for each oil change. Lycoming says if you fly often, you can extend that 4 months some

Bavafa:

Here is the link to Lycoming's website that says 25-hours oil changes on engines with a pressure-screen system.

Lycoming Service Bulletin 480 goes into a lot of detail on Oil Servicing...

 

[Bavafa]

Bavafa:

Here is the link to Lycoming's website that says 25-hours oil changes on engines with a pressure-screen system.

Lycoming Service Bulletin 480 goes into a lot of detail on Oil Servicing...

Isn't the 'pressure screen system' the screen that we are suppose to inspect every 100 hours or each annual. If so, yes I knew about that and it makes sense but it has been a long time that I have seen a Lycoming engine without spin on oil filter that relies only on that screen for filteration.

 

[DanH]

Parts per million is a concentration. It has nothing to do with particle size. For example, the substance measured could be entirely dissolved. If a solid, one part per milion could a single particle or 100 particles 100 times smaller.

Blackstone has a nice article here regarding their spectrometer: https://www.blackstone-labs.com/spectrometry-the-marvel-of-the-lab/

Monday morning, call Blackstone or LabOne and ask if their ICP spectrometer is insensitive to large particles. I think you're going to get the answer to your mystery. Poor filtration of particles >10µm is seen in an inexpensive oil analysis as higher insolubles, because the spectrometer can't process them as parts per million.

Brad, does LabOne report insolubles?

Quick reading:

Tactics For Identifying Wear Metal and Solid-particle Suspensions

The most widely used laboratory methods for initial detection of abnormal levels of wear debris in used oils include elemental analysis, ferrous density analysis (DR, etc.), particle counting and...

www.machinerylubrication.com

Spectroscopy for Large Particle Measurement

For the last forty years or so, spectrometric analysis of lubricating oils has been used to determine the concentration of wear metals, contaminants and additives present in oil samples. This...

www.machinerylubrication.com

 

[RV6_flyer]

Isn't the 'pressure screen system' the screen that we are suppose to inspect every 100 hours or each annual. If so, yes I knew about that and it makes sense but it has been a long time that I have seen a Lycoming engine without spin on oil filter that relies only on that screen for filteration.

The Lycoming Parts manual (PC-103) for my O-320 call the oil filter screen item 4 part number 62817 "SCREEN ASSY., Oil pressure".


I would call the oil pickup tube screen the one that we inspect at least at the condition inspection. Lycoming parts catalog call it "SCREEN, Oil suction".


When I acquired the engine for use in my RV-6, it had the screen to filter the oil and I changed it to a spin on filter like most newer engines came with.

 

[ChiefPilot]

Parts per million is a concentration. It has nothing to do with particle size. For example, the substance measured could be entirely dissolved. If a solid, one part per milion could a single particle or 100 particles 100 times smaller.

Blackstone has a nice article here regarding their spectrometer: https://www.blackstone-labs.com/spectrometry-the-marvel-of-the-lab/

Monday morning, call Blackstone or LabOne and ask if their ICP spectrometer is insensitive to large particles. I think you're going to get the answer to your mystery. Poor filtration of particles >10µm is seen in an inexpensive oil analysis as higher insolubles, because the spectrometer can't process them as parts per million.

Brad, does LabOne report insolubles?

Quick reading:

Tactics For Identifying Wear Metal and Solid-particle Suspensions

The most widely used laboratory methods for initial detection of abnormal levels of wear debris in used oils include elemental analysis, ferrous density analysis (DR, etc.), particle counting and...

www.machinerylubrication.com

Spectroscopy for Large Particle Measurement

For the last forty years or so, spectrometric analysis of lubricating oils has been used to determine the concentration of wear metals, contaminants and additives present in oil samples. This...

www.machinerylubrication.com

That's a question worth asking, and kind of what I was trying to get at previously but didn't use the correct vocabulary with them. They do in fact provide particle "counts" if you are willing to spring for the report; that is separate and distinct from the PPM measurements and what I was referring to. There's an example on their website I took a look at, but as I mentioned I didn't really think anything of it previously. Probably worthwhile now.

 

[Bavafa]

The Lycoming Parts manual (PC-103) for my O-320 call the oil filter screen item 4 part number 62817 "SCREEN ASSY., Oil pressure".
View attachment 61055 View attachment 61056

I would call the oil pickup tube screen the one that we inspect at least at the condition inspection. Lycoming parts catalog call it "SCREEN, Oil suction".
View attachment 61057

When I acquired the engine for use in my RV-6, it had the screen to filter the oil and I changed it to a spin on filter like most newer engines came with.

I was wrong, I thought item 17 is what you are referring to. I have not seen an engine with the type that you have. This goes to show that I am still very much a rookie

 

[DanH]

That's a question worth asking, and kind of what I was trying to get at previously but didn't use the correct vocabulary with them.

I was asking if they report an insolubles value with their standard spectrographic report. There isn't one on the post # 8 example. Blackstone does; see Mehrdad's report.

Blackstone discusses insolubles here: https://www.blackstone-labs.com/what-are-insolubles/

Fun with numbers...assume Mehrdad was running six quarts, or 1.5 gallons at 7.29 lbs/gal for Phillips 20W-50. That's 10.935 lbs, or 4959 grams. The Blackstone report gives the most recent insolubles as 0.4%. If by weight, that's 19.83 grams of solid material circulating in the engine. If volume, about 7.7 fluid ounces.

It's not all dirt. Some of it would be lead byproducts, soot, wear metals...anything which won't dissolve. The insolubles value doubled when switching to the screen filter, but it's a very small statistical sample.

Mehrdad, that report was dated 2020. Have anything more recent?

They do in fact provide particle "counts" if you are willing to spring for the report; that is separate and distinct from the PPM measurements and what I was referring to.

Separate test involving a laser counter or similar. The multipass system at the filter lab uses Pamas counters: https://www.danhorton.net/VAF/Filter Test Results/Pamas 4132 Particle Counter.pdf

Probably worthwhile now.

If you want to learn particle size.

 

[Bavafa]

Fun with numbers...assume Mehrdad was running six quarts, or 1.5 gallons at 7.29 lbs/gal for Phillips 20W-50. That's 10.935 lbs, or 4959 grams. The Blackstone report gives the most recent insolubles as 0.4%. If by weight, that's 19.83 grams of solid material circulating in the engine. If volume, about 7.7 fluid ounces.

It's not all dirt. Some of it would be lead byproducts, soot, wear metals...anything which won't dissolve. The insolubles value doubled when switching to the screen filter, but it's a very small statistical sample.

Mehrdad, that report was dated 2020. Have anything more recent?



If you want to learn particle size.

All correct assumption Dan. Here is one additional report that I found but I will look more as I couldn't find the most recent ones.

 

[DanH]

All correct assumption Dan. Here is one additional report that I found but I will look more as I couldn't find the most recent ones.

That one shows insolubles dropping back to 0.2%, but it was only 19 hours. Still not conclusive one way or the other.

BTW, here's an illustration which may help with understanding. The ISO 4548-12 filter efficiency test records particle counts and sizes in the green shaded range. The ICP spectrometer would detect the elemental components of particle sizes in the red box or smaller, but can't detect the larger particles. The solubles test should detect all solids, but bear in mind the very small sample size,

 

[airguy]

That one shows insolubles dropping back to 0.2%, but it was only 19 hours. Still not conclusive one way or the other.

BTW, here's an illustration which may help with understanding. The ISO 4548-12 filter efficiency test records particle counts and sizes in the green shaded range. The ICP spectrometer would detect the elemental components of particle sizes in the red box or smaller, but apparently can't detect the larger particles (to be confirmed). The solubles test should detect all solids, but bear in mind the very small sample size,

View attachment 61070

The spectrographic indication would appear to be the market of interest for wear-inducing particles, given the oil film thickness restriction between the rings and the cylinder, and assuming a similar oil film thickness in the bearings. Larger particles in the green SHOULD be filtered out by a decent filter - which was the question that started all this.

 

[Snowflake]

Guys, it was my understanding that it was “recommended “ to change the oil more often with a washable filter? Is that not the case? Seems like most are changing every 50hrs regardless. I’m curious because cost, wise that had previously pushed me to a spin on type filter.
I thought 25 hrs for washable and 50 for “standard” spin on disposables. I’m following these discussions closely.

Maybe you're thinking of the difference between running with just a screen (in which case Lycoming says 25 hours) vs running with a filter + srceen (Lycoming says 50 hours)?

 

[ChiefPilot]

I can't really get the information I need from LabOne, so current plan is to do the pending oil change and send a sample to Blackstone (really like their reports; just never investigated them before and LabOne was what I'd seen used etc.). That report will be the most recent 50hrs on the reusable filter. The next 50 hours will be on a paper filter, and I'll get a Blackstone report on that too.

What I'd like to do, in addition, is estimate the amount of retained "stuff" caught by the paper filter. Not really sure how to go about doing that, however. Since the used filter will have junk plus an oil-saturated element, one approach would be to soak fill the new filter with clean oil and let it sit a bit to saturate, then drain the oil and weigh it for the baseline. Weigh the filter again after taking it off in 50 hours and draining the oil out then subtracting the baseline weight should give a reasonable approximation of how much "stuff" the filter caught. I have a reloading scale which should be more than accurate and precise enough for this. Goal is to get an idea of how much stuff is coming out of a reasonably healthy, mid/high time engine.

Perhaps there is a better approach?

 

[DanH]

I can't really get the information I need from LabOne...

They had no information regarding the insensitivity of the ICP spectrometer to particles greater than 10 µm?

 

[ChiefPilot]

They had no information regarding the insensitivity of the ICP spectrometer to particles greater than 10 µm?

None that they have been able to share as yet.

 

[Strikhedonia]

I switched to a Challenger oil filter (and have had two oil changes/oil analysis reports since then), prior to that I was using Champion filters. Attached is my oil analysis report that lists before and after (no change).

 

[DanH]

None that they have been able to share as yet.

Ok. Know nothing about LabOne, but the folks at Blackstone are happy to educate. Just got off the phone with one of their guys. They consider the upper detection threshold for their ICP spectrometer to be 15 µm. It's blind to anything larger.

As noted in a prior link, the industry considers 10 µm as a practical detection limit. All the filters are roughly similar at 10 µm and less, so yes, the spectrographic silicon counts should be similar. The screens rapidly become useless above 10 µm, but you can't see it in a spectrograph report.



We also talked about insolubles. The reported value is the percentage of the sample by volume. We're talking, ballpark, one half of one percent of a very small sample, and it's all the garbage lumped together. Although they do not routinely identify the makeup of the insolubles, past experience says it's mostly lead. Put another way, a change in silicon content would be a variation of a small percentage of a small percentage.

Bottom line, a spectrographic oil analysis tells almost nothing about filter performance.

 

[Bavafa]

I switched to a Challenger oil filter (and have had two oil changes/oil analysis reports since then), prior to that I was using Champion filters. Attached is my oil analysis report that lists before and after (no change).

This is consistent with my experience, judging by the Blackstone lab results.

 

[plehrke]

Bottom line, a spectrographic oil analysis tells almost nothing about filter performance.

Agree. Oil analysis and oil filters perform different functions. That is why I do both.

 

[Bavafa]

Agree. Oil analysis and oil filters perform different functions. That is why I do both.

But if we are comparing the results of using two different oil filter in the same plane and same environment, wouldn't that be the most complete test for our purpose of use of filter.

Granted filter A does a lot better than filter B but if some of those condition that it was tested under does not exist in our use case, will it make it as relevant?

 

[airguy]

But if we are comparing the results of using two different oil filter in the same plane and same environment, wouldn't that be the most complete test for our purpose of use of filter.

Granted filter A does a lot better than filter B but if some of those condition that it was tested under does not exist in our use case, will it make it as relevant?

Only if the flight profile and environmental conditions were identical for the 50-hour changes involved for that aircraft, and nothing changed on the engine with respect to wear patterns.

Too many variables in a real-world operating environment.

 

[ChiefPilot]

Only if the flight profile and environmental conditions were identical for the 50-hour changes involved for that aircraft, and nothing changed on the engine with respect to wear patterns.

Too many variables in a real-world operating environment.

In a pedantic sense, sure. But in a real world sense there is some value to be gained. I am genuinely curious how much crud a good filter is going to pick out of the oil, and I doubt the minor variances in conditions or flight regimes will have much of an effect on that.

 

[airguy]

In a pedantic sense, sure. But in a real world sense there is some value to be gained. I am genuinely curious how much crud a good filter is going to pick out of the oil, and I doubt the minor variances in conditions or flight regimes will have much of an effect on that.

Much of my normal flying is done in the Texas area and desert southwest, lots more dust exposure (silicon) there than my recent trip to the Bahamas which put 30 hours on the airplane in dust-free environments, that's most of an oil change. There is no way to pick out that kind of variance from the data you are looking for other than adding an asterisk to the conclusion.

 

[ChiefPilot]

Much of my normal flying is done in the Texas area and desert southwest, lots more dust exposure (silicon) there than my recent trip to the Bahamas which put 30 hours on the airplane in dust-free environments, that's most of an oil change. There is no way to pick out that kind of variance from the data you are looking for other than adding an asterisk to the conclusion.

Ok, then this thread probably won't be of any further interest to you. But it's of interest to me in the flying I do, and if someone else finds it interesting that's fine too.

 

[ChiefPilot]

Ok. Know nothing about LabOne, but the folks at Blackstone are happy to educate. Just got off the phone with one of their guys. They consider the upper detection threshold for their ICP spectrometer to be 15 µm. It's blind to anything larger.

As noted in a prior link, the industry considers 10 µm as a practical detection limit. All the filters are roughly similar at 10 µm and less, so yes, the spectrographic silicon counts should be similar. The screens rapidly become useless above 10 µm, but you can't see it in a spectrograph report.

View attachment 61392

We also talked about insolubles. The reported value is the percentage of the sample by volume. We're talking, ballpark, one half of one percent of a very small sample, and it's all the garbage lumped together. Although they do not routinely identify the makeup of the insolubles, past experience says it's mostly lead. Put another way, a change in silicon content would be a variation of a small percentage of a small percentage.

Bottom line, a spectrographic oil analysis tells almost nothing about filter performance.

Dan, once again, thank you. I get the picture now after talking with you and several others. Thanks for being willing to share what you've learned and thereby raising all our collective knowledge.

 

[JonJay]

Dan, once again, thank you. I get the picture now after talking with you and several others. Thanks for being willing to share what you've learned and thereby raising all our collective knowledge.

Yay Dan!

 

[DanH]

I am genuinely curious how much crud a good filter is going to pick out of the oil...

All of it

Seriously, how much is exactly what the 4548-12 tells us, in percentage removed for every particle size from 4 to 40.

I suspect you meant how much it's going to pick out the oil when the engine lives in a clean environment. Answer is not much.

That said, remember, even in a perfectly clean atmosphere a good filter remains the last bulwark when an engine begins to come apart due to internal damage. For most of us it's a practical matter...It gets us to the next oil analysis and filter cut without ruining parts.

 

[Bavafa]

Only if the flight profile and environmental conditions were identical for the 50-hour changes involved for that aircraft, and nothing changed on the engine with respect to wear patterns.

Too many variables in a real-world operating environment.

We are not talking about just one sample but multiple people and multiple sample from each person. And a reminder that we are not using these as a shuttle to outer space.

 

[planenutz]

There has been some great information on these threads and I congratulate Dan on starting a great conversation.

On the subject of SOA analysis, there is a common misconception that the sampling process provides you with information on all the "junk" in your oil, however it doesn't. The machines that analyse samples are looking for parts per million and prior to your oil being subjected to the full process, filters remove the big chuncky bits out of the sample. If they did not do this then your oil sample will clog up the machine and they have to stop the production line and clean it. It's not in their interest to shut down the line when they have 200 samples to get through in 2 hours.

I often get customers who call for advice after finding metal on their engine chip plugs. The first question they usually ask is - "should I send an oil sample to the lab?" The simple answer is "No". Sending a sample which is full of chunky bits is very unlikely to show any significant change in the trends of your engine because those chunky bits get removed from the sample before the oil is analysed. If you want to know what the chunky bits are then you need to send these away to a facility with a SEM and have them anaylsed that way. The particle analysis process is different to the SOA process and tells you a different part of the story.

So what I'm getting at here is (in answer to the OP's question) - the "junk" floating around in your oil is likely bigger in size than the parts per million that the SOA process is looking out for and those chunky bits are removed from the sample before testing. So yes... changing oil filter types is not likely to make any difference to your SOA results, but perhaps not for the reasons you might think.

Personally I am not in favour of the SOA process for most general aviation applications. Why? Because we tend to replace the oil regularly. The SOA process is great for monitoring your Kenworth truck that might do 200,000 miles before a gearbox oil change, but for engines where the oil is replaced every 25 - 50 hours it really doesn't give you the fidelity you need. If you don't believe me or feel the need to flame me, please go and visit your local SOA Lab and get them to give you a guided tour. You might be very surprised by what you find out and I think it will help answer some of the questions... certainly dispell many of the assumptions... people have on how it all works.

 

[Bavafa]

There has been some great information on these threads and I congratulate Dan on starting a great conversation.

On the subject of SOA analysis, there is a common misconception that the sampling process provides you with information on all the "junk" in your oil, however it doesn't. The machines that analyse samples are looking for parts per million and prior to your oil being subjected to the full process, filters remove the big chuncky bits out of the sample. If they did not do this then your oil sample will clog up the machine and they have to stop the production line and clean it. It's not in their interest to shut down the line when they have 200 samples to get through in 2 hours.

I often get customers who call for advice after finding metal on their engine chip plugs. The first question they usually ask is - "should I send an oil sample to the lab?" The simple answer is "No". Sending a sample which is full of chunky bits is very unlikely to show any significant change in the trends of your engine because those chunky bits get removed from the sample before the oil is analysed. If you want to know what the chunky bits are then you need to send these away to a facility with a SEM and have them anaylsed that way. The particle analysis process is different to the SOA process and tells you a different part of the story.

So what I'm getting at here is (in answer to the OP's question) - the "junk" floating around in your oil is likely bigger in size than the parts per million that the SOA process is looking out for and those chunky bits are removed from the sample before testing. So yes... changing oil filter types is not likely to make any difference to your SOA results, but perhaps not for the reasons you might think.

Personally I am not in favour of the SOA process for most general aviation applications. Why? Because we tend to replace the oil regularly. The SOA process is great for monitoring your Kenworth truck that might do 200,000 miles before a gearbox oil change, but for engines where the oil is replaced every 25 - 50 hours it really doesn't give you the fidelity you need. If you don't believe me or feel the need to flame me, please go and visit your local SOA Lab and get them to give you a guided tour. You might be very surprised by what you find out and I think it will help answer some of the questions... certainly dispell many of the assumptions... people have on how it all works.

Mike,
My interest here is learning and arguing endlessly and possible drawing a logical conclusion at the end. Having said that, wouldn't one expect those big chunky items be caught by the filter and would mostly apply to those planes that lack a filter and rely only on a screen?

 

[rocketman1988]

Mike,
My interest here is learning and arguing endlessly and possible drawing a logical conclusion at the end. Having said that, wouldn't one expect those big chunky items be caught by the filter and would mostly apply to those planes that lack a filter and rely only on a screen?

Someone once said, jokingly, that anything caught by the suction screen would be large enough to have a part number on it. The perforation hole size in that screen is about .050" which is over 1200 microns. That's comparatively the size of a boulder.

 

[DanH]

Mehrdad, the "big chunky bits" are those particles 10 µm and larger.

The spectrograph is blind to particles above 15 µm, and doesn't always detect solids in the 10 to 15 range. Larger particles are not reflected on your oil analysis.

The Challenger and S-15 screens catch a few particles below 10 µm...roughly 3x less than a Champion or a Tempest, but a few.

From 10 µm to around 100 µm, the Challenger and S-15 don't really catch anything. Above 110 µm or so they do catch, but the larger particles clog them very quickly.

....wouldn't one expect those big chunky items be caught by the filter and would mostly apply to those planes that lack a filter and rely only on a screen?

Operators with a depth media filter can expect the efficiency values posted previously. Those with screens are not filtering much of anything under 100 µm.

 

[planenutz]

... wouldn't one expect those big chunky items be caught by the filter and would mostly apply to those planes that lack a filter and rely only on a screen?

As Dan just explained above, we're talking about relative sizes here. The "really big chunky bits" that your filter removes are huge compared to the particles which still get past your oil filter media, but even those tiny particles are still very big compared to what the SOA machine is looking for.

When you have an engine suddenly "make metal" the SOA process is often unlikley to return anything abnormal, because if you can see it with the naked eye then its far to big to be placed into the spectrographic analyser. I've had many customers come to me with a fairly normal SOA result yet the filter is full of metal particles.

 

[Bavafa]

Mehrdad, the "big chunky bits" are those particles 10 µm and larger.

The spectrograph is blind to particles above 15 µm, and doesn't always detect solids in the 10 to 15 range. Larger particles are not reflected on your oil analysis.

The Challenger and S-15 screens catch a few particles below 10 µm...roughly 3x less than a Champion or a Tempest, but a few.

From 10 µm to around 100 µm, the Challenger and S-15 don't really catch anything. Above 110 µm or so they do catch, but the larger particles clog them very quickly.



Operators with a depth media filter can expect the efficiency values posted previously. Those with screens are not filtering much of anything under 100 µm.

Thank you Dan for explaining this in a way that I can understand. Would it be correct to explain this as following; we don't see much different results in the oil analysis with different filters because those larger particles are prefiltered by the SOA process and this is why we don't see them in our report. If those were not prefiltered, then we should expect to see much more with the S-15 type than Champion.

 

[Toobuilder]

Personally I am not in favour of the SOA process for most general aviation applications. Why? Because we tend to replace the oil regularly. The SOA process is great for monitoring your Kenworth truck that might do 200,000 miles before a gearbox oil change, but for engines where the oil is replaced every 25 - 50 hours it really doesn't give you the fidelity you need.

Yep, this tracks with my early training as a jet engine troop in the USAF. Oil is almost never changed in a turbine and if it does get changed, the the entire oil sample trending needs to start from scratch. It’s really a pain to start those records over because it is a trend analysis, not a point analysis. The more points you have, the better sense of a trend. The overall trend is where you make the decisions. The first several samples on new oil are basically worthless and you are “blind” from a maintenance perspective.

 

[planenutz]

Yep, this tracks with my early training as a jet engine troop in the USAF. Oil is almost never changed in a turbine and if it does get changed, the the entire oil sample trending needs to start from scratch. It’s really a pain to start those records over because it is a trend analysis, not a point analysis. The more points you have, the better sense of a trend. The overall trend is where you make the decisions. The first several samples are basically worthless and you are “blind” from a maintenance perspective.

Nailed it.

My turbine helicopter customers are typically doing oil changes at 500 or 600 hour intervals... or about every 6 months. You can't trend monitor anything off that.

 

[DanH]

Thank you Dan for explaining this in a way that I can understand. Would it be correct to explain this as following; we don't see much different results in the oil analysis with different filters because those larger particles are prefiltered by the SOA process and this is why we don't see them in our report. If those were not prefiltered, then we should expect to see much more with the S-15 type than Champion.

I think there is some confusion in the above.

The preparation of a submitted oil sample includes multiple steps, one of which may or may not be filtration to protect the test equipment. Typical ICP spectroscopy is blind to solid particle sizes above 10 µm, so removing those particles prior to test makes no difference in the final result. Filtered or unfiltered, same result.

Put another way, you don't see the elements contained in the large particles because it's a limitation of ICP spectroscopy, not because of any sample filtration.

Good basic online article here, with a quote below: https://www.machinerylubrication.com/Read/287/elemental-analysis

The test equipment vendors post much more detailed information.

Influence of Particle Size
The major limitation with AES is that because the method requires excitation of individual atoms, the sample must be fully vaporized to allow all atoms present to be measured. While this is not a problem for small particles and dissolved metals, the probability that a particle can be vaporized and analyzed using AES drops very rapidly above 5 microns. In fact an AES spectrometer is all but blind to particles in excess of 10 microns.