912ULS Oil Analysis

[Dan Kent]

Below is the oil analysis on my 912 ULS. The plane was flown to Sebring in January of this year and used several tankfuls of 100 LL, but never used any 100 LL on this oil interval.

 

Thought I would post this for others to compare to.

[Roger Lee]

Hi Dan and All,

 

Here are some thoughts.

First one report doesn't usually (it can depend) make a sample a major concern. You need to show a trend. If you have one report that is questionable then shorten the next oil change and do it again. If you do 100 hr. oil changes (you shouldn't) then readings may be higher. If you do the 50 hr changes and get a questionable report then do another at 25-30 hrs. If you are using 100LL then then the oil should have been changed at 25 hr. and if it wasn't then high lead levels will show. Taking a sample when the oil is cold verse hot will show a difference. Taking a sample at the beginning of the oil drain, at the middle or at the end will show different readings too. Catch the sample in the middle of the oil drain. I don't know anything about Blackstone, but I do know AvLabs system. They have many thousands of samples from Rotax 912 engines to compare to. You compare engines with the same approximate time on them. The sample gets run 3 times to assure accuracy. The samples are shown in Green (good), yellow (keep an eye on it) or red (this may be a problem). Samples can get contaminated too. If something is in the red from Avlabs and there is other items on the list that support a serious problem they will call you direct. Usually if one item on the list is really serious then there is usually something else on the list that supports the problem. Other supporting items during an inspection may be things like a fury mag plug and or lots of metal in the oil filter. If you have a high lead reading maybe it's time to clean the oil tank.

 

This engine only has 99 hrs and I personally don't catch oil samples until they hit 200. Then I do them at the annual. That is usually every other oil change for many that fly around 100 hrs. a year. Every 100 hrs (or Annual)is fine, every 50 is a little over kill unless you are trying to weed out a problem. A new engine is breaking in that first set of hours and the Mfg's assembly sealants and metal parts are breaking in which may give a higher readings over a later oil sample.

[FredG]

It would be nice to know what the reliability of these measures are. Specifically, if a sample is split and sent to the same lab, will the values be the same? Furthermore, if two samples are taken from one engine, say 24 hours apart, and sent to the same lab, how variable are the results? If two samples are taken and sent to different labs, how similar are the results? The answers to these questions drives the interpretation of differences between observed results and the lab average.

 

Next, universal averages are nice, but the real question is the distribution of values, not just the arithmetic mean. Hence, the lab should really give the average and the 25th, 50th, and 75th percentiles, or, if the distribution is normal, the mean and standard deviation.

 

Finally, the real question is whether the values predict some bad outcome. For example, do engines with copper levels of 16 ppm (as shown in the attachment) have a shorter lifespan than those with 7 ppm (the "universal average" for the laboratory)? If yes, then the value of 16 ppm matters. If not, then a copper concentration of more than twice the average is no problem. I suspect that such information is only anecdotal (although potentially valuable).

 

My final question is, for an engine making good compression with no metal on the magnetic plug nor any in the filter (and that has not been abused), does the oil test add meaningful information to operating safety or engine longevity? Do you do anything differently? If not, why get it?

 

Fred

[Roger Lee]

Hi Fred,

 

Oil analysis will tell you things you can not see on a mag plug or filter inspection. Only large chunks or magnetic materials show up on the above. They are just one tool of the things to consider.

Baring having your own lab we are stuck with their analysis and expertise. If you want to test your theory then buy 6 test kits from three companies and test your questions. all samples will have to be caught at the same time and within a narrow scope of the oil drain.

[FredG]

Roger and other list members,

 

Without reliability information, understanding the reported oil analysis values is difficult.

 

Regardless, the question remains, for an engine that has good compression, nothing in the filter, no fuzz on the mag plug, and no history of abuse (overheating, wrong oil, etc), does oil analysis predict future engine failure?

 

Also, does an atypical oil analysis change how the pilot should operate the engine or how the mechanic should maintain the engine? If none of these things change, what is the purpose?

 

Fred

[Roger Lee]

Hi Fred,

 

It's only one tool in your proverbial toolbox. It can show a problem in progress, but can it predict all engine failures, no. Read the blog on the lifter failure, no warning. You have to use all your tools to piece the puzzle together. One piece doesn't make a puzzle. Same for a doctor with a blood analysis. It can't predict the future, but it could find something now or that is just starting. For the $20 once a year and with the thousands of dollars worth of lab equipment, thousands of other samples to compare to and the expertise to interpret the results my money will have to go to the analysis.

Look at it this way, it's better than nothing and that $20 may save you thousands.

If you do it once a year at $20 and even at 20 years that's only $400 over 20 years. What would you have to loose, nothing, but you may gain something. Just one tool in the many over the life of the engine.

[FredG]

Hi Roger,

 

I think we are asking different questions. My question is simple, do I, as a pilot and 912 owner, do anything differently with an engine that has good compression, etc (see above) but a funny value on oil analysis? Do I take it out of service? What do I do other than get more oil analyses and get them at even more frequent intervals? Check compression more often? Check the filter and mag plug more often?

 

Although I don't want to bring clinical medicine into this, it is important to remember that some tests help clinicians manage patients and some tests add nothing to their management (or even make it worse). Good medical practice requires getting only tests that will modify patient management for the better. My question is, what does oil analysis add to engine management? How might it save me thousands?

 

Stated another way, "the expertise to interpret the results" means that the results change something - hence my question, do I do anything differently with an engine that has good compression, etc (see above post) but a funny value on oil analysis? If yes, I'm happy to add oil analysis it to my maintenance. But, so far, I don't see that anything indicating that operating and maintaining the engine changes as a function of oil analysis, which is fine.

 

Fred

[Roger Lee]

Hi Fred,

 

You said it right here:

"Do I take it out of service? What do I do other than get more oil analyses and get them at even more frequent intervals? Check compression more often? Check the filter and mag plug more often?"

 

The answer is yes to all and hopefully it was a bad sample or it may point to an impending issue or one already in the making. Don't do an analysis and run it until it fails in the air with a passenger on board. I bet the passengers around you will give you the $20 once a year.

 

You can have good compression and nothing on a mag plug, but have an ailing engine. Read what was sent to Dan in his explanation. Copper/bronz can be from just a new engine breaking in and an older engine signs of early valve guide failure and bushings in the crankcase. Lead when no lead is in use may mean early signs of bearing failures. Compression has nothing to do with oil analysis unless you have let it go undiscovered so long your engine is already trashed. Bad compression may be an acute sign of a failure or a late stage finding after the fact. You don't always need to take it out of service. It may alert you to an on coming issue or it may be nothing and just needs to be monitored by an earlier oil change next time. As far as you doing anything different with the findings is determined by what is found.At least an oil analysis may give you a heads up to where a problem is starting to manifest. Find it and fix it early is usually cheaper than waiting for a complete failure.

 

You money can be saved be an early recognition and repair before you have an totaled engine.

 

An oil analysis is a path. Stand at the beginning of the path and you'll never see what's at the end or along the way until it's too late. Walk the path and see the things you might possibly miss and the path may take you to an end where you may find a problem before it finds you. Then hopefully a solution is cheap at hand.

 

 

There aren't any absolutes with an oil analysis because many things can influence them so we keep walking the path a short ways and continue looking. Maybe if we are lucky we walk that path forever and never see any thing.

 

 

It's still only one tool in your fly safe arsenal.

[Doug G.]

So if I understand what you just said, Roger, you have actually taken a plane/engine out of service based on oil analysis with no other obvious indications?

Doug G.

[Roger Lee]

Hi Doug,

 

I never have personally, but others have. . I haven't seen anything that would need to take a plane out of service over one oil analysis.

[FredG]

Roger,

 

I did read the text provided by the oil analysis company - they wrote "Monitor this engine for a bearing problem". What does that mean? How does one do that on a 912? If it doesn't get better, does the engine get taken out of service? Why not monitor every engine for a bearing problem? Isn't that safer?

 

What if the engine had 1000 hours and ran perfectly? Would you split the cases to inspect the mains? How many 912's have stopped running because they spun a bearing that was detected early by oil analysis?

 

What is the repair that saves me thousands for a 20 dollar test?

 

Fred

[Roger Lee]

Hi Fred,

 

The oil analysis may show a bearing wear before you see metal on the mag plug. It is only a heads up and to watch the next check to see if it continues to become worse. You do monitor every engine for bearing failure. That is why you are supposed to check the mag plug every oil change and Rotax says you should do an oil analysis for the 2000 hr. TBO. I will say that finding particles in the oil filter will be the last place you find major evidence. There have been engines opened up before failure do to on going detailed inspections which may include mag plug checks, oil filter inspection, oil analysis, compression test, rough running, case fretting, ect... Like I said it's only one tool, you have to put them all together for the complete puzzle.

[Dan Kent]

Here's some more information on my engine. The sample was taken shortly after the engine had been warmed up. It was extracted from the oil tank via vacuum. This was the 3rd oil change for this engine. The first was at about 23 hours (I beleive Rotax requires the first service to be at 25 hours). 100LL was in use for approximately 4 hours of this 23 hours. The 2nd oil change was performed the same way and by the same mechanic. The mag plug has been checked at all 3 oil changes with some normal amount of build up. The 2nd change was at 66 hours (43 hours on the oil). Of these 43 hours, 100 LL was used for approximately 6.5 hours.

 

I'm estimating the hours from my logbook, and of course 100 LL was still in the plane tank even when I switched back to Mogas, but the intervals above were flight times after 100 LL added up until Mogas was used. Decalin was used for all 100 LL additions.

 

I've done quite a bit of analysis with Blackstone for automotive applications. I also called them before testing to see how much Rotax analysis they have done and said they had hundreds of samples in their database (I think this is correct - their response was enough to reassure me of the value of using them, plus my past automotive experience).

 

Just as a final note, one of my coworkers was considering purchasing an extended warranty for his truck as the manufacturer's warranty was due to expire in a few weeks. I suggested that he should probably do an oil analysis just to see if anything showed up and it may help him make his decision. He sent in a sample to Blackstone. They called him and said that there was antifreeze in his oil and that this particular engine had a tendency to develop a leak at a particular cylinder. Anyway the co-worker was able to get the repair done by the dealership under warranty and also got another year of engine warranty from the dealership, so in this instance the $20 paid off.

[Roger Lee]

Hi Dan,

 

Here is where I think your high levels of lead came from. It was the way the sample was taken.

You used suction to remove the oil so depending on where that tube was in the oil would have a big affect on the sample. If it was down in the tank closer to the bottom then very high levels of lead would show up because that's where the lead sits. Suction taken too high in the oil would cause very little metals to show and more of the other products. When taking samples at different oil changes it may be unlikely you take it in the same spot in the tank depending on who is doing it. I would catch my sample off the bottom. Let 1-1.5 qts. drain then catch the sample mid drain. You don't want a bottom sample and you don't want it from the top of the oil.

[Doug G.]

Sorry Roger, I remain unconvinced of the value of oil analysis. How many ppm means real engine damage? Unless my engine is dissolving quickly, I will see it in the filter analysis, the mag plug, or the compression. I believe if Rotax thought it was significant they would recommend it long before TBO.

[Roger Lee]

Hi Doug,

 

I believe you mis-understood.

"I believe if Rotax thought it was significant they would recommend it long before TBO."

 

Rotax wants you to do an oil analysis every 100 hrs or at least by the annual.That's in writing. That's what I meant by 18 oil analysis. Starting at 200 hrs. (my number, not theirs) that would 18 samples until you hit the 2000 TBO. I'm not even a believer in the TBO, just solid maint to that point and beyond. Good maint. practices will take this engine to 3k-4K hrs without major issues.(with an exception now and then). I get many calls everyday and answer even more emails from poor maint. practices that cost these guys hundreds of dollars if they are lucky and thousands if they aren't. I have the unique importunity with my mechanic relationships in the industry to see more than the average Rotax mechanic and talk to all the owners with problems and get to see what led to those problems. Problems as we know are usually a set of events that lead up to that moment.

Many insurance companies won't cover what caused the crash like a seized engine just the parts you damaged on the crash landing. So the expensive engine would be your burden.

[Runtoeat]

Hi Dan. Wondering if your mechanic removes the oil reservoir, takes it apart and cleans it out at each 100 hour or if this has not been done yet? Eventhough I use Mogas, my mechanic pulls the reservoir and cleans and inspects it at each 100 hours and it always has a coating of lead on the bottom. Removing and cleaning the reservoir is somewhat of a PIA but he does this as a matter of course on all aircraft he services. If it hasn't been done, and even if you are using Mogas only but you are suctioning oil out of the reservoir for the oil sample, this may be the reason for the high lead content in your oil samples. You probably have a fair amount of lead sitting on the bottom of your reservoir even if using Mogas and the small amount of 100LL fuel you have used. When the drain plug is pulled, an amount of lead flows at first but the rest remains stuck to the bottom. If you use Roger's technique of letting some oil drain and then catching a sample, this may give a better sample for analysis.

[FredG]

Where does Rotax specify that they "want" owners to do an oil analysis every 100 hours (or annually)?

I just did an electronic search of the Maintenance Manual (Edition 2/Rev. 0, October 01, 2009) for "oil", "oil analysis" and "oil analyses" and cannot find such a recommendation.

Thanks.

Fred

[Doug G.]

Found it! 05-20-00 page 5 in the maintenance manual recommends a number of additional inspections including oil analysis. They spell it differently.

[Doug G.]

Roger, this is what I was responding to, "That is why you are supposed to check the mag plug every oil change and Rotax says you should do an oil analysis for the 2000 hr. TBO."

 

Also, Dick, how do you end up with lead from fuel that has no lead in it???

 

Doug G.

[Roger Lee]

The mag plug will show up only ferrous metals, but the engine also has non-ferrous metals that you won't see on the plug or in the filter and you may not see the starting signs of excessive wear by the naked eye. An analysis is the only way to keep an eye on things.

Lead can come from bearings and other parts. Lead can be left over from older times of 100LL use in the bottom of the oil tank and if the sample was collected wrong it may show a spike in the readings.

Another place to find references to the oil analysis is in Rotax bulletins.

 

 

 

Ferrous Metals:

 

Carbon Steel

Alloy Steel

Stainless Steel (some)

Tool Steel

HSLA Steel

Steels for strength

Iron-based superalloys

 

Non-Ferrous Metals:

 

Aluminum

Beryllium

Copper

Magnesium

Nickel

Refractory Metals

Titanium

Zirconium

[Dan Kent]

Hi Dan,

 

Here is where I think your high levels of lead came from. It was the way the sample was taken.

You used suction to remove the oil so depending on where that tube was in the oil would have a big affect on the sample. If it was down in the tank closer to the bottom then very high levels of lead would show up because that's where the lead sits. Suction taken too high in the oil would cause very little metals to show and more of the other products. When taking samples at different oil changes it may be unlikely you take it in the same spot in the tank depending on who is doing it. I would catch my sample off the bottom. Let 1-1.5 qts. drain then catch the sample mid drain. You don't want a bottom sample and you don't want it from the top of the oil.

 

Thanks Roger for clarifying this. I was under the impression that the mineral oil portion of the semi-synthetic mix kept lead in suspension, so the lead would be somewhat uniformly distributed throughout the tank.

 

Hopefully the next oil change will be at annual where the mechanic removes the oil tank and cleans it. I'll ask him to get a sample from the middle of the drain.

[Dan Kent]

Hi Dan. Wondering if your mechanic removes the oil reservoir, takes it apart and cleans it out at each 100 hour or if this has not been done yet? Eventhough I use Mogas, my mechanic pulls the reservoir and cleans and inspects it at each 100 hours and it always has a coating of lead on the bottom. Removing and cleaning the reservoir is somewhat of a PIA but he does this as a matter of course on all aircraft he services. If it hasn't been done, and even if you are using Mogas only but you are suctioning oil out of the reservoir for the oil sample, this may be the reason for the high lead content in your oil samples. You probably have a fair amount of lead sitting on the bottom of your reservoir even if using Mogas and the small amount of 100LL fuel you have used. When the drain plug is pulled, an amount of lead flows at first but the rest remains stuck to the bottom. If you use Roger's technique of letting some oil drain and then catching a sample, this may give a better sample for analysis.

 

Hi Dick,

At the last oil change I was discussing this with the mechanic and he says he pulls and cleans the tank at annual. He says most of the planes he services doesn't reach 100 hours by annual, but in my case he will disassemble the tank and clean it at my annual. I'm planning to do more flying now that the weather has cooled down some so hopefully I'll be in the 130 -150 hours by the time I reach my annual.

 

Thanks for your experience with this. I never would have guessed that you could visually see the lead leaving the tank. Do you use Mogas exclusively? If so where is the lead coming from?

 

Dan

[FredG]

Doug, good find.

 

Rotax makes this hard to understand. They recommend oil analysis (spelled oil "analyse") once in the entire maintenance manual. It is in a table in chapter 05-20-00, "Scheduled Maintenance Checks", but in a section called "Unscheduled maintenance checks" and under a subheading called "Recommends inspections [sic]". Immediately above the table Rotax writes "The manufacturer also recommends the following inspections whenever maintenance is carried out". The question remains, given the name of the chapter, do they mean whenever scheduled maintenance or unscheduled maintenance is carried out?

 

Also odd is the omission of oil analysis from the "Maintenance Schedule" table on page 13 of Section 05-20-00 and its omission from sections on unscheduled maintenance for a) exceeding of maximum admissible engine RPM, exceeding of maximum cylinder head temperature, c) exceeding the maximum permissible oil temperature, d) oil pressure below minimum value and e) oil specification not respected.

 

In contrast, the word pair "oil filter" appears on twenty separate pages of the manual (with multiple mentions on many of those pages). Oil analysis is never mentioned in any section where oil change or oil filter inspection (including opening the oil filter) is recommended.

 

Hard to understand what Rotax really wants here. Time to get a German speaker to look at the authoritative German versions and assist with our understanding.

 

I like the engine but I am not thrilled by the documentation.

 

Fred

[Runtoeat]

Dan, I use Mogas only but I see that there is a thin layer of lead "sludge" on the bottom of my reservoir when it is removed and cleaned. Not sure why because the Mogas isn't supposed to have lead. Perhaps there's some lead in "non-leaded" Mogas? I know that eventhough it is supposed to be "low lead", 100LL fuel has a lot of lead in it so perhaps Mogas has some? There are guys on this thread that have commented on the chemical makeup of fuel and perhaps they could comment on this. Removal and cleaning of the oil reservoir may be optional if Mogas is used because there isn't much lead found. Just another low cost preventative thing to do. The bottom line is I hope that all is well with your Rotax and there are no problems. A comment on lab testing. The diesel engine durability department where I worked before retiring used chemical oil analysis as one of the main tools to evaluate new engine designs or cost reduction changes to existing engines. Running compressed durability on dynomometers, oil analysis is used as an early indicator to determine if unacceptable wear may be ocuring. Part wear analysis at teardown inspection normally supported the oil analysis.