Posted for Walter Atkinson <walter@advancedpilot.com>:

 Matt:
 
 According to Lycoming, any CHT above 150dF is adequate for operation.  TCM,
who does not publish a low limit as such, sets the water-cooled engine to run
constantly at 240dF (same barrels, same pistons and rings) so something lower
than 240 is OK.  The data from TCM suggests that they think the low limit is
somewhere around 200dF.  Based on this information and our experience, 285dF
is NOT too cool.  I broke in my engine with CHTs no more than the high 290s to
the low 300s and it was finished breaking in at 3.5 hours.
 
 I have heard many claims over the years that cylinders need to be hot to
break in, but I have never seen any data to support that and have a lot of
experience and data which refutes it.
 
 If your oil consumption has not stabilized at this point something is
definitely wrong.  It could be too low a ring tension.  Maybe too wide on the
ring gaps.  Maybe glazing (although they seem to have ruled this out).  Could
even be the WRONG rings are installed.  That's happened before.  But,
something is wrong and I'll bet that it's not your cool CHTs.
 
 Walter
 
 

"""
 The engine runs too cool.  With 180 hours on since 0-timed, the rings have
 not seated.  I am burning 1 quart of oil every 2 hours.
 
 I took it to the (reputable) overhaul shop, who boroscoped it and pronounced
 the cylinders to be like new, still with cross-hatching, and no glazing.
 
 We discussed my operating temperatures - about 285 degrees (300 max on a hot
 day) in cruise.  They say "too cool, it will never break in at those
 temperatures".
"""