Thanks for the reply!

Intresting thought... I may just have to check that out.. Last weekend, when I completed the change-out, I thought I addressed the air pocket possibility adequately. I refilled the system, and ran the car briefly to raise the temp up enough to turn on the heater pump. After being satisfied I had adequately replenished the water, I drove the car for a bit, with the heater on full blast (it was a bit cooler last weekend). a couple of days later, I topped off the reservoir as it had dropped a bit as the car had completely cooled down (level was about 3/4 inch below indicator). On my shake-down run, I did not drive very far, or get out of the city, so today was really my first chance to check everything out. I guess an air pocket could still be hanging around; however, as I returned from my trip this evening, I was running the heater on 20C or so in auto mode to keep the cabin a bit warmer (ambient temp was 47F). Car behaved as earlier in the day...