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Tell me about oil analysis in a piston engine

Picking up from another thread it would be interesting to understand why other operators use oil analysis on piston engines. Have worked at various organizations (AOC, ATO) and while oil analysis is definitely carried out on turbine equipment, no operator that I have come across does oil analysis on their piston fleet.

Is this oil analysis a statistically proven preventive maintenance practice for low utilization piston operators? I understand it takes several analyses to establish a base line trend, but unless the air cooled, low compression, high blow back ring, piston engine is operated in a very consistent manner, it is quite easy to create trend vectors that deviate from the trend: mixture and power setting, OAT/DA, short, cold start operations, long range operations. This is fundamentally due to the antiquated design of the engine.

The oil filter is pretty unambiguous, and like the entrails of a sacrificial goat, will give you reliable augurs that your engine is making metal (beyond the odd trace) and/or making carbon on the valves. A quick borescope can then follow.

While I get it that some of the bearings may create metal trends which are of interest, and which inspecting the oil filter might not reveal, but the engine will be showing other signs of distress through the goat entrails method.

Perhaps the oil analysis firms have some marketing literature explaining why oil analysis is a proven preventative maintenance measure on the herd of Conti and Lyco -saurii? I somewhat suspect they see this as a niche side line from their turbine business.

Oxford (EGTK), United Kingdom

ATO aircraft fly so often with frequent oil changes, I am not sure what oil analysis would show other than new oil and healthy engines running all the time?

I guess on privately owned aircraft that fly less where the oil analysis will show something: like the engine is not flying very often as it should?

Last Edited by Ibra at 25 Jan 10:18
Paris/Essex, France/UK, United Kingdom

RobertL18C wrote:

Is this oil analysis a statistically proven preventive maintenance practice for low utilization piston operators? I understand it takes several analyses to establish a base line trend, but unless the air cooled, low compression, high blow back ring, piston engine is operated in a very consistent manner, it is quite easy to create trend vectors that deviate from the trend: mixture and power setting, OAT/DA, short, cold start operations, long range operations. This is fundamentally due to the antiquated design of the engine.

I think if you have a fairly utilised fleet, then there is a chance you might catch some engine problems in time – at least you could order a new engine, if you know you would have to replace it soon anyway.
Potential savings on downtime for a very small expense?

EGTR

To a large degree, this practise is promoted by Mike Bush from Savvy Aviation:
https://resources.savvyaviation.com/client-resources/savvy-oil-recommendations/

QUOTE:
Oil Analysis
We also recommend starting the use of or switching to Blackstone laboratories for oil samples. They do a much better job than other labs in our experience, and have the newest state-of-the-art equipment. Free oil sample kits may be ordered online at:
https://www.blackstone-labs.com/free-test-kits.php
Make sure the oil sample results are emailed back to you (not the Service Center), and post the Blackstone report to the Savvy ticket system when you get it. We suggest you fill out the oil analysis submission form yourself to ensure that the data is accurate.

Last Edited by Niner_Mike at 25 Jan 11:13
Abeam the Flying Dream
EBKT, western Belgium, Belgium

Clubs and ATOs generally send perfectly good engines to overhaul before 2500h, so why do oil analysis ? Club a/c regularly make 50hrs per month in the summer.
Private owners benefit more from oil analysis to help troubleshoot issues early and generally extending the calendar life of the engine. And CAAs start to take oil analysis seriously as a engine health indication.

LFOU, France

I would surmise that a private owner, concerned (and probably emotionally invested) with a single machine is more likely to perform oil analysis as part of their dedication to its upkeep.

A fleet operator will view it from a more business-like perspective – do I save money doing this versus not doing it? They will have the finances of their business planned out based on utilisation, planned maintenance costs, TBO, etc. Perhaps one thing that makes a major difference is that they’re overhauling at TBO regardless of whether compressions and perhaps oil analysis suggest they might be good for another thousand hours?

Frequency may be an issue. Aircraft in a busy piston fleet might be having their oil changed every 7-10 days and the analysis costs would soon add up. A private owner may only do it a couple of times a year.

Then you have the question of what you actually do with the information. @Peter has asked this before – will anyone actually pull the engine apart based solely on what the oil analysis shows? Can many owners afford to? Each engine will wear however it is going to wear (obviously depending on factors such as manufacturing / assembly quality coupled with usage and storage) and it is a matter of debate how useful it is to be aware of the details of that as you go along. The refurbishment or replacement costs will arise whenever regardless, and it is for this reason that operating finances are often structured with an engine fund based on $X per hour.

This last debate is not unlike Covid-19 testing. What do you actually do differently, for that patient, when you know the result? Almost always, nothing.

Last Edited by Graham at 25 Jan 11:37
EGLM & EGTN

Actually AOC and ATOs will tend to send engines for OH at TBO plus the regulatory allowance, say 10% or 20%.

How many private operators go beyond TBO because they get oil analysis? I would consider OH on condition when oil useage is increasing, compression is deteriorating, and/or the oil filter looks unacceptable (quite obvious to tell).

Oxford (EGTK), United Kingdom

RobertL18C wrote:

Actually AOC and ATOs will tend to send engines for OH at TBO plus the regulatory allowance, say 10% or 20%.

How many private operators go beyond TBO because they get oil analysis? I would consider OH on condition when oil useage is increasing, compression is deteriorating, and/or the oil filter looks unacceptable (quite obvious to tell).

Yes sorry – what I mean is that under their regime the engine is going for OH at a certain number of hours regardless of condition – so why monitor the minutiae of that condition, especially in the latter part of its life?

I don’t think private operators go beyond TBO and operate on condition because of oil analysis, but it might be one tool that helps them be comfortable with doing so. They might just have more emotional investment in that particular unit than a fleet operator who views an engine as a business commodity?

I have an old-fashioned attitude to this. If it runs ok and feels/sounds/looks ok, then it’s probably ok. As you say, compression, oil usage, filter evidence. I find most claims of oil usage on engines in decent shape over-blown (literally). Both the PA17 and TB10 (Conti C90 and Lyco O-360 respectively) appear to use almost nothing between oil changes so long as you don’t overfill them. On both aircraft I know the point on the dipstick where, if you fill it past there, you’ll find it back there after a brief flight. That being the case, actual usage will become very obvious when it happens.

EGLM & EGTN

no operator that I have come across does oil analysis on their piston fleet.

That’s probably true, but for the wrong reasons. The “business” of GA generally knows little about “mechanical things”. It was only Deakin who dragged GA kicking and screaming into the late 20th century, and this got through to only those who actually “read stuff” and “think about stuff” – maybe a few % of owners, and zero renters, and zero schools, and definitely zero maintenance companies who remain as clueless on operations as ever and continue to spread scare stories about leaning. In the US, a bit more generally, due to a bigger population of “analytical” owners compared to Europe which basically struggles, with the one-eyed man being the king in the land of the blind

Is this oil analysis a statistically proven preventive maintenance practice for low utilization piston operators?

Not sure about “low” specifically but one example is here.

Another is here.

These are easy actions based on oil analysis.

If it runs ok and feels/sounds/looks ok, then it’s probably ok

Generally that is true, but it’s a matter of risk management. Not all major failure mechanisms make big particles. With the massive torque in use, you could be chewing up some bearing (due to an oil gallery offshoot being blocked) really nicely and will never notice it on performance, not until the bearing is red hot, and there won’t be any metal in the filters because it is way too fine. The engine won’t sound any different until a conrod pops out through the crankcase Oil analysis costs practically nothing (~25 quid per 50hr check) and it gives you a level of reassurance that there is nothing horrible going on inside the engine.

If you just fly locally, then “who cares” but I fly over the Alps and over lots of water and I like to not worry too much. Look at the GA scene, and look at how many won’t do any of that. Look at how many people fly to Le Touquet all the way along the coast to Dover so they cross the shortest over-water distance.

I’ve just bought a new high pressure fuel pump, £250, based on the 1.5% fuel in the last oil analysis, because that’s exactly what I had a few years ago. 250 quid is peanuts, especially as my TB20 maintenance costs are so low.

It is like flying at night. I have almost 3k hrs TT but only ~30hrs at night, and it is partly because it is bad risk management. The other reasons of course are the well rehearsed ones: airports shut etc. Or not going to unknown grass; just because everybody tells you “it is perfect” they may all be flying Maules with tundra tyres.

will anyone actually pull the engine apart based solely on what the oil analysis shows?

If no metal was found in either oil filter? If I had lots of tin I would open it up ASAP.

Or one might get an engine, making way too much metal in the oil, done at say 1800hrs rather than wait a bit longer, especially if it convenient for some other reason…

Remember that the Lyco guidance on how much metal in the filters is “ok” is quite scary. They measure it in spoons… Conti, I believe, gives no guidance.

The other oil analysis threads are well worth reading.

Administrator
Shoreham EGKA, United Kingdom

The thread of eight years ago was interesting. As suggested, easy to get into false positives. The engineers I know are ex heavy iron and with a strong practical and engineering knowledge, including turbine analysis.

Am not suggesting this is a cost issue, just that the ‘science’ seems to be somewhat soft and the practical benefits do not seem to be quantified, scientifically.

Votive candles are quite cheap I believe:)

Oxford (EGTK), United Kingdom
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