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>> Number 3 cylinder (IO-360 B1F) runs consistently hotter than the rest by
30 degrees or so and crowds 450 degrees during climb, 400 or a touch more
during cruise (leaned for best power).  I've tried cutting away more exit
area on the right cowl side, no good.  I plugged the heater duct which
draws from that side's rear baffle, no effect.  I pulled the heater SCAT
tube out completely because it might be obstructing air flow under the
cylinder fins, no good (and a
lot of work too!) I swapped probes (who knows), nope.  Oil temps run 165
to 170 degrees normally.  The Lycoming guy thinks the 400 is OK but is a
little nervous about the 450.  The baffling seems OK but I'm not super
confident about it. <<

Ed,

This is pretty normal, though 450 is too hot to hit routinely if you want
the engine to last a long time.  #3 being hottest is quite common and
fixing that is usually a matter of altering the intake flow pattern with a
diverter of some kind.  Some have had success with a curved diverter
located above the #1 cylinder that helps move air directly towards #3.
Failure of your other "fixes" means you are probably getting good pressure
distribution side to side.  You just need a tiny bit more air across #3.
30 degrees is not that much really, not that trying for less is a waste of
time.

165 to 170 on the oil is actually a bit low.  The vernatherm should
be regulating to 180.  Unless you are getting at least 180, then you
should restrict some of the air across your oil cooler.  This is sometimes
necessary only in cooler weather.  I have a plate I install on my Mooney's
oil cooler in the winter but not in the summer.  Don't let the oil get much
above 230 though.  If you don't get at least 180 on the oil, you are not
boiling off the moisture the crankcase collects when you are not flying and
corrosion will likely cause an early overhaul.


 - Doug Dodson
   Glasair II-S FT
   Flight Test Engineer, CFI-A,G
   Baby Dragon IF1 Race Team
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