REFLECTOR: Lycoming break in oil

[Andrew Ellzey]

I am considering using Phillips 66 X/C 20W-50 engine oil http://www.phillips66aviation.com/AvLubricants/XC_20W-50.htm for my IO-540 0 SMOH engine. Phillips also makes  a type M 20W-50 break in oil http://www.phillips66aviation.com/AvLubricants/Type_M_20W-50.htm. The Phillips 66 X/C 20W-50 literature makes the following claims, X/C 20W-50 is the first approved multiviscosity aviation oil for opposed piston engines. It provides better engine performance than any single grade oil in all weather conditions. X/C 20W-50 is formulated with an ashless dispersant package allowing for cleaner engine operation. (((X/C 20W-50 is recommended for break-in))). It provides a cleaner and quicker break-in than traditional all mineral single grade oils. Plus, X/C is an operational oil so there is no need to switch oils after break-in. X/C 20W-50 utilizes all petroleum base oils which provide excellent solvency and is successful in preventing lead and lead salts.
 
The Phillips 66 M 20W-50 makes these claims, Type M is generally recommended and used as a break-in oil for newly overhauled aircraft engines. Type M is generally used by engine overhaul and repair shops for the initial run-in of aircraft piston engines. Type M 20W-50 is designed for owners and pilots who want the performance of a multi-viscosity, mineral based piston engine aviation oil without dispersant additives. Type M contains the same high quality base oils and viscosity index improvers found in renowned X/C aviation oils. 
 
The only difference that I see is that the M doesn't contain the dispersant additives. Has anyone on the reflector used either of these oils for your break in oil and what were your results? I like the fact that with the X/C 20W-50 I won't need to use two types of oils after the break in.
 
Andy Ellzey
XLRG