[slovcan]

People who are smarter and more experienced with the 75 than I say an airlock is the likely culprit. Who am I to argue with that? They're probably correct.

The one other thing that comes to mind, though, is the possibility that the heater core (matrix) may still be restricted with the remnants of the goop that was put in to fix the original leak. That stuff is just evil. Some heater cores have smaller passages than radiators. I'd be prepared for another flush - maybe even just the core through the heater hoses and with a cleaning agent or vinegar or something. If the drain/refill process doesn't do the job...

Good luck,
Glenn