I would also not use that solvent method. It risks damaging the front oil seal, although if done right the stuff should not reach the level of the oil seal.
My experience has been that too many hours of low power flight does bung up the cylinders, though I am not sure whether it is the piston rings, or glazing on cylinder walls, or both. However, it has not happened to me since I originally reported it. I cleared it with high power running.
Some old posts above are disingenuous i.e. the owner didn’t actually do what he posted…
Re bunged up crankshafts, this is one example. The OP never came back but I heard years later that his crankshaft was solidly plugged with some kind of debris. Hard to imagine where it may have come from – there is the filter after all.
planewrench wrote:
For research, i pulled a pa28 181 POH and looked at the cruise information… If read correctly, the POH says to consult the Lycoming ops manual for the engine (o360 series. )
Well… At least our PA28-181 has a POH with proper power setting diagrams for 55%-75% power.
Of course everyone has that correct?
Actually, yes!
For research, i pulled a pa28 181 POH and looked at the cruise information… If read correctly, the POH says to consult the Lycoming ops manual for the engine (o360 series. ) Of course everyone has that correct? In the Lyc ops manual, while they have data for less power settings,, they pretty much consider 65% the lower end “cruise” data point with 75% the upper. Interesting and had not looked at it in a long time. ( i have a 77 172N) I personally run 70% all the time. One more interesting note, Lyc says 140 degrees MIN inlet for oil temp. So they actually specify a number, which i had never seen before. If you do not have the Lyc ops manual, worth getting as technically, the POH at least for this piper, says you have to consult it for ops. The piper POH does give numbers for lower power settings, but other than the Lyc info, no preference as to what you SHOULD use. From a tech standpoint, i would personally recommend 65% as min power for cruise, why? I want the higher temps in the oil system, better combustion scavenge , as well has a higher BMEP in the cylinder to seal rings against the cylinder walls. Less blow by , especially in the long runs.
Sludge, looks like grey clay mud that will build up in hollow crankshafts. Combo mostly of oil deposits and contaminates with bit of lead from fuel. Basically a by product of using the crank as a centrifuge for lack of better description. Can be 1/4 inch or more you have to scrape out. This is why frequent oil changes are important, especially if you have a lot of cylinder blow by. Sludge can also be in the sumps, never drains out all the way on some engines. Not really dangerous, normally seen on hi time or abused engines.
Because practically nobody is selling UL91 
What is this sludge made up of?
My answer to everything is lean aggressively, unleaded Avgas and Aeroshell 15W50.
Peter if this is your aircraft why not fill not tank with UL91 and use that for the cruise?
Thank you @planewrench for that professional view. I very much appreciate that!
planewrench wrote:
As far as running engines at 50%… if the poh and lyc or tcm have charts for that low power settings
Yes it has, and yes I monitor CHT and oil temps closely. Interestingly enough (at least for me 
) my engine seems to have an oil cooler bypass valve, which seems to be the reason why my engine keeps the oil temp quite well.
That is what I was thinking right from the start. When the temperatures are fine, noise and vibration are fine, there should be in principle no limitation to run an engine in any power setting. That in mind: too low power settings that lead to potential damage in the long run will be indentified by too low oil temps. I assume that about 180 °F could be a lower limit for “good temp”.
Hello Europe
Cylinder glazing is as mentioned in one thread, happens as a result of improper breakin. I would say its impossible to have it happen in service, no matter what oil or power setting you may use.
Hi consumption will be a result of glazing at break in. In later hours, there are more factors, including insufficient choke or wear due to improper installations and in TCM systems, fuel scheduling.
As far as the “procedure” as mentioned, the only person that has talked about it is Mike B. I can pretty much guarantee. that he has never personally signed a log book using that procedure. Lyc has SI’s that counter that process. There is NO way to get all the contaminants out of the case and cylinders after you fill a cylinder expecting to loosen and free up stuck rings. This is something farm boys do. Myself and other IA’s here in the states are shocked at the idea of such a process.
As far as running engines at 50%… if the poh and lyc or tcm have charts for that low power settings, you should be fine…. Key is being able to have oil TEMP in the good range to burn off contaminates. I would suggest more frequent oil changes and perhaps use of straight weight oils as added precautions for longevity. CArl
What is true about RPM: if I set low RPM isn’t cylinder pressure higher, so low power and low RPM is fine?
And this is where it all gets complicated…
There are sooo many configurations, engine brands, oils, ops Ts, flying or operating styles, that any conclusive evidence remains as an isolated experience.
E.g. I’ve now flown my baby for > 1’200hrs in 4 1/2 years, most of this time at between 40 to 50% power settings, and guess what? The oil consumption is exactly the meager same 1qt/50hr as it was when I started enjoying her (…), and the cylinders, which get borescoped every 100hr show no less no more glazing either.
Steering back to the title of the thread, suspecting sludge build-up associated with an increased oil consumption would mandate the flushing procedure in the cylinder(s) concerned.
I agree with all except possibly #3:
extended periods of low power flights do not lead to glazing if you do the occassional normal flight
I can’t quantify it but perhaps 30hrs, all at high altitude (say FL170), non turbo, can bung up the rings on my IO540-C4.
In practice, in GA, this very rarely happens.
