This may not be much help to Ev at this point (I think he's gotten the idea about "burping" these babies), but here's a "hack" that helps illustrate the point of the high point of the circulation system and may help someone else: when my heater core died a painful death a few years ago I decided just to route around it (I rarely ever used that heater thingy anyway in the climate I'm in). The pic below shows the hose with filler access port (yellow arrow) that I use to bleed air from the system; the looping hose just skips the through-the-firewall part [shortening the hose loop a bit is on my to do list with the engine out]. Just do the normal refill procedures as in the manuals, but I leave the port slightly opened as the fluid gets hot (put some shop towels around to catch the spatter from the air bubbles) and do the final fill though the port.
I think this topic has received a lot of replies because we've all dealt with this "lovable quirk" of these otherwise wonderful little cars. I first discovered this issue with my first Spider ('76 model) when we lived in New Orleans in the '70s - and yes, stuck in traffic in a "nefarious" part of town, heater turned wide open, me sweating bullets. Hang in there Ev.
