Hi All,

I had a bit of excitment today that was cooling system related.  Flew
this AM for about 1.4 hours (6.5 hours total) with no problems and was
delighted to see I'd finally got the heavy left wing resolved.  This
afternoon under a warm spring sun I took off, had just climbed to 4500'
and found it was actually warm enough to turn the cab heat off for the
first time this year.  About 10 seconds after turning off the flow of
coolant to my heater core I could smell something and a slight white
smoke came up from under panel.  Pulled the power back, radioed the
tower I could smell something and headed back to the circuit.  Smell and
smoke appear to have cleared  while decending and I made a normal
landing with the emergency trucks there to greet me at the taxi way.
When I got to the hangar I first started to look under the panel for
something that was heat damaged but everything looked fine so I removed
the cowl and really could not see much wrong there either untill I
noticed a bit of moisture on the overflow line from the coolant
expansion tank.

So what I think happened is, turning off the flow to the heater core
caused a pressure increase in cooling system which burped a bit of extra
coolant into the expansion tank which was enough to cause it to overflow
the tank which had a too short of hose on it so it dripped a bit of
coolant on the header pipes which caused the smoke.  Before I fly again
I'm going to switch over to the pressurized recovery tank and move the
location over to the cool side of the engine as I prefer not seeing
trucks with flashing lights waiting for me to land.

Perry Casson