An increase in oil consumption over a short period is obviously worth investigating. I would imagine that you have already checked the plugs and looked at the cylinders with an endoscope? Compression test? One plug dirtier than others and slight scoring of the bore would be a cracked ring.
My engine uses 1 qt per 4 hours, this is exactly in accordance with the manual’s “normal” consumption. The sump holds 9 qts, I normally fly with max 8 qts. I reduced that now to max 7 qts will see if that makes a difference.
One result of high oil consumption is that over 50 hours I use 13.5 qts, i.e. 150% of my normal sump capacity. Why would I need to change oil very 25 hrs?
Compression test? One plug dirtier than others and slight scoring of the bore would be a cracked ring.
All fine. Comps are 78-79/80.
One result of high oil consumption is that over 50 hours I use 13.5 qts, i.e. 150% of my normal sump capacity. Why would I need to change oil very 25 hrs?
The oil doesn’t get changed on a FIFO basis 
The new oil is merely diluting the crap in the old oil. I could put 8 qts of topups into my engine (over a 50hr period – i.e. exactly the same as yours, per hour) and the oil, when drained, is as filthy as ever.
The topups will undoubtedly dilute the oil analysis results, so one needs to allow for that.
We did however find, on the last service, last week, a leak from one of the little flexible hoses which carry oil down from the rocker covers. So we replaced it, and will replace the rest at the next service.
If the leaking hose is the culprit it means you would have dumped a 1qt of oil overboard in the last 10 hrs. That would be very noticeable on the engine and the belly of the plane.
If it is stuck/clogged rings why would it effect all pistons at the same time?
With a tiny leak, which exists only during engine running, there may not be anything on the cowling if the stuff is vapourised.
Time will tell…
achimha wrote:
achimha 17-Aug-15 11:12 #10
Peter wrote:
it is widely suggested, and makes good sense, that very low oil consumption means that the engine is not getting well lubed
Well, I do not believe that at all and have not seen anything of substance backing such a claim. More looked like poor attempts to justify the poor quality of the engines and turning a vice into a virtue.Peter wrote:
and it correlates with sticky valves (which you had)
That wouldn’t make much sense at all. To the contrary, oil entering the combustion chamber (which is how a Lycontosaur loses oil during operation, apart from leaving through the crankcase breather) contributes to crud getting between valve and valve guide. Valves are a little bit cooled by oil flowing through the cylinder head but again, the more you lose (by burning), the more crud in the valve guides. So I would claim the opposite is true.
Achim check out Lie number 5 http://www.avweb.com/news/maint/182849-1.html
He wrote a more extensive article in AVWeb but cant find it right now. It talks about sticking valve guides.
I have been in contact with Ed Kollin. There are specific serious risks involved with the procedure in that document. Nobody should be doing it unless they understand e.g. valve timing. Letting the solvent get through the valves and into the intake poses, at best, making a mess and at worse, a potential fire.
If low consumption resulted in insufficient piston/barrel lubrication, one would see the consequences of that in the oil analysis (abrasion). What I’m saying is that .75qt in 25h is a perfectly healthy oil consumption and there is no data that would allow to draw the conclusion that these 1950s engines need to burn more oil than that.
1qt in 4h like in the example above is a very high oil consumption and while I wouldn’t necessarily take action (= very expensive) I would thoroughly investigate the reason.
The 1 qt/4hr in my engine is normal. When these engines are younger I have had 1qt/6 hrs but that slowly increases with age.
What’s important is the rate of any change in consumption. If it’s slowly progressive over hundreds of hours it’s probably OK, short term changes are not.
Peter wrote:
Nobody should be doing it unless they understand e.g. valve timing. Letting the solvent get through the valves and into the intake poses, at best, making a mess and at worse, a potential fire.
How do you want to push the solvent by the piston rings if a valve is open? So yes, not being a complete n00b does help 
Ted.P wrote:
One result of high oil consumption is that over 50 hours I use 13.5 qts, i.e. 150% of my normal sump capacity. Why would I need to change oil very 25 hrs?
Because the percentage of ¤]@§*$¤ in the oil sump increases by just about the same factor – think “distillation” .
Because of this, you will find that oil consumption actually goes down with more frequent changes.
Achima’s example is typical: he only consumes .5L in the first 25H of ops, but I’m willing to bet that hew would “burn” X4 that amount if he changed oil @ 50H ops.
