When my cooling system had air in it (this is an 84) all kinds of strange
symptoms resulted.  The temp gauge would run up to the flashing indicator
light, then drop right to the coolest reading...Then come back up, at
unpredictable intervals.  All of a sudden, my heater would start blowing
cold air (it was last fall).  Then, due to overheating of the motor but no
indication on the temp gauge, my headgasket let go..Inline four motor, so I
fixed it in about 4 hours right in the van.  The motor was overheating but
at the same time, the heater was blowing cold air...Odd, but probably a
result of some kind of air lock in the circulatory system...
  So after fixing  the headgasket and replacing all the hoses and other
coolant related stuff...water pump, thermostat, rear heater valves, front
heater valves...I was somewhat paranoid about how much air the cooling
system was holding...
  That is when I figured out to pour coolant right into the bleed screw to
finish the bleeding process and make SURE no more air was in there...
  Now, as  part of my  regular eminence plan, before I take a long road
trip, I change oil, filter(cut it open to check for metal bits) check the
belt tension and top off the rad. through the bleed hole...For about 10
months now, I only find room for a few shots of coolant...but I still
check...
  Don Hanson