While I've been playing with the cooling system measurements, I decided to
look into a nagging symptom that I've had since building the airplane.  The
cooling system has never remained completely topped off and seemed to loose
a small amount of coolant (~ 2 oz) on every flight.  This didn't seem to be
a problem because the cooling system works OK until its about two quarts low
and I check and top off the system long before that happens.

I have a one quart overflow bottle which is about the only size the
aftermarket brands offer (I used Moroso) so I assumed this was adequate for
any installation.  To test this, I ran the hose from the overflow port on
the overflow bottle to the cockpit and connected it to a second bottle.
Sure enough, when the engine got up to full operating temperature, the hose
puked a couple of ounces into the second bottle.   When the engine cooled to
room temperature, it recovered all the coolant in the first bottle then
sucked in a bit of air.

Moral of the story:  Use a coolant recovery bottle larger than 1 quart.  I
just installed a 1.5 liter bottle.  Will flight test this setup tomorrow.

I also noticed that cooling was noticibly better when the system was
completely full of liquid  with absolutely no air in it.  Even a few ounces
worth of air in the system caused the coolant temp to go up about 5 - 7
degrees.  The amount of air did not seem to affect it much. Anything from 3
oz to 60 oz of missing coolant has the same effect on temperature. I don't
know the exact cause of this temp increase.  More than 60 oz missing causes
the temps to rise rapidly (I think the pump starts sucking air at this
level).

Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com