Interesting that you chose PSA testing as an analogy. Seems to me that FOBT is more analogous to the subject since in both cases a positive test result leads directly to a, ahem, boresope 
I try to always respect others’ risk assesment and believe that it is a very personal matter if there ever was one. That said and independent of yours or anyone elses personal choices, the usefullness of Oil Analysis is not very clear to say the least.
You get a load of metal in an oil flter and you can be 99.99% sure that somethings coming apart in the bottom end. On the other hand, you get a high reading of X, Y or Z in your oil analysis and then you go hunting for the culprit, but the vast majority of the time you never come even close to conclusively determing the exact cause, hence “false positives”.
Not opening an oil filter is just plain negligent and I can only advise owners to demand to see the filter element after every single oil change.
Well, with abnormal PSA you have the 3T MRI option, for ~1000 quid. With an engine, you can’t inspect the internals without at least pulling off a cylinder (a stupid design – they could have put in an inspection plug).
If anyone is interested in comparing Blackstone in the USA with another arbitrary company, I have some duplicate oil samples (which I took in case of sample loss in the post to the USA) and I have the Blackstone analysis for these. Normally I would chuck them away but they seem useful for this purpose.
Just bumping this thread for the last post above. I am accumulating these duplicate oil samples. They are free of charge (except for postage if outside the UK) to anyone who wants to check consistency between their oil analysis lab and Blackstone.
I use Blackstone too and think picking one outfit and staying with it is more important than exactly which one is best unless some are known to NOT be reliable.
Reading back up the thread a bit following the bump, I’m amazed hearing a) how many owner pilots flying around that don’t do OA or any of the other steps below, b) how many discussions there are around a single data point of any kind, and c) how many don’t have and use engine monitor data for analysis
A single OA result alone has limited value. The big value of OA is the history over time and comparison of the results to other data points. I have 20 years of OA for my engine and most result fluctuations seem correlated to my flying frequency.
Engine condition monitoring should be a package, with as many data points as possible reviewed together before initiating any remedial action to a perceived problem:
- OA per oil change, specific results plus comparison to history and flight profiles
- cut open filter and review contents …. volume, piece size, and type of metal.
- borescope
- spark plug review and testing
- flight test profiles with subsequent data analysis: high altitude mag check, GAMI profile
- compression (note: last on the list and probably the least relevant)
Interesting comment on Compressions.
When the engine is running the compression is probably irrelevant unless there is so much gas blowing past the piston rings that it is forcing too much oil out of the breather (or oil consumption rises massively)
So my question to everybody is what is the lowest compressions you would feel happy flying with (assuming all cylinders are more or less the same) and oil is not being consumed at a huge rate?
Once you get behind (and have to pay for)a big bore continental you quickly either have a nervous breakdown or learn to almost ignore compression values.
I have been told by many that they are not easy to check reliably.
If I pull the prop through when cold, it is surprising how little compression there is. It’s marginally better just after landing but not like my old IO360 180hp.
However it always fires on the 1st rotation, seems to have all the power I need and more, flies happily at the performance the book predicts (allowing for manufacturer salesmanship),
and doesn’t move on the dipstick between oil changes. Go figure.
Relevant threads here and here, among others.
The reason low compression doesn’t lose power is because everything happens so fast that the gases don’t have time to escape through whatever is leaking.
But you ignore this at your peril, because if e.g. a valve is not seating this is likely going to overheat pretty fast – see e.g. here – and when it fails properly you will definitely notice 
That event has been an eye opener for me, making me check low RPM running very very carefully, both immediately after startup (the best time to show up sticky valves) and before departure, check all EGTs one by one, and then again immediately after landing, again checking the EGTs at idle. IOW, poor compression does show up at low RPM – as you would expect.
For some reason Conti have very low airworthiness limits on their compressions, compared with Lyco. I don’t know why. It’s a much discussed topic. Some say it is poor manufacturing by Conti. On a Lyco IO540 you expect to see 77/80 or better for the whole TBO, although the exact number depends on whether the engine has just been run, etc.
The current corona virus discussion – which is obviously running all over the place, with much sanctimonious pontificating about whether human life is worth more than some engine – highlights that almost nobody does oil analysis, and thus is not going to know if there is corrosion… until their camshaft starts to relocate itself into the oil filter but hey that is not a problem because the plane will be sold by then
I am tempted to have oil analysis done at the coming annual. I have never done it before.
As I have an engine monitor, I do keep a beady eye on everything as much as possible.
I have 1 slight anomaly in that when rich at Idle all temps CHT/EGT are similar but when lean at Idle cylinders 1&2 have noticeably higher EGT. When in the cruise they are all quite even again. It’s been like it since before she was mine.
I mentioned it to the mechanics but they didn’t think anything was a cause for concern.
That’s fine.
