alioth wrote:
Looking at that Lycoming document, it has a formula for the maximum allowable oil consumption of an engine – it turns out that Lycoming only consider an O-320 to be consuming excessive oil when it reaches 1 quart every 2 hours (which seems awfully high to me!)
I guess that the limit is set only to make sure that the engine does not run out of oil before it runs out of fuel!
That (fuel capacity) would be an airframe issue, not one the engine manufacturer is concerned with 
It is very strange that the airworthiness limits are set so high. For a 540 (almost 2x bigger) it is something like almost 2x higher i.e. about 1qt/hr. This is atrocious and would indicate something severely wrong with the pistons/rings. It doesn’t indicate wear elsewhere because all the oil pressure-fed to the bearings gets recycled, so a worn engine just runs with a lower oil pressure.
However I did manage to achieve such a high consumption, by bunging up the piston rings. This was solved with an unapproved method involving Mobil 1 0W20 for 5hrs before a service (I never wrote this). That engine was later dismantled (I did an engine exchange) and overhauled and was found to be pretty perfect.
I don’t know what mechanism Lyco had in mind for the very high oil usage but if it was anything else to the above then it must be something fairly serious.
For those of us who are moderately inclined to read the engine manufacturer’s instructions:
Lycoming Reciprocating Engine BreakIn and Oil Consumption
Lubrications Oil Recommendations
PART II – OIL RECOMMENDATIONS FOR ENGINE OPERATION AND BREAK-IN
A. All turbocharged engines must be broken-in and operated with ashless dispersant oil only.
B. O-320-H; O/LO-360-E series engines may be operated using either straight mineral oil or ashless oil. However, if the engine is delivered with ashless dispersant oil, it must remain on ashless dispersant oil. The Textron Lycoming oil additive P/N LW-16702 must be added to the O-320-H and O/LO-360-E engines at airframe installation, and every 50 hours thereafter or at every oil change. This lubrication recommendation supersedes the lubrication recommendations in Service Instruction No. 1392.
NOTE
If it is determined that a FAA approved lubricating oil being used contains, in the proper amount, an oil additive equivalent to LW-16702, the provisions of this Service Instruction are met.
C. In all IGSO-480 and IGSO-540 series engines equipped with Simmonds fuel injection systems, it is al- lowable to use SAE50 or SAE60 grade lubricant providing the engine oil pressure does not exceed the limits set forth in the Operator’s Manual.
D. All other engines must be operated on mineral oil during the first 50 hours of operation, or until oil consumption has stabilized. LW-16702 additive may be used. If an ashless dispersant oil is used in a new engine, or a newly overhauled engine, high oil consumption might possibly be experienced. The additives in some of these ashless dispersant oils may retard the break-in of the piston rings and cylinder walls. This condition can be avoided by the use of mineral oil until normal oil consumption is obtained, then change to the ashless dispersant oil. Mineral oil must also be used following the replacement of one or more cylinders or until the oil consumption has stabilized.
