RE: Cooling Problems in an '85
You are going to get a bunch of answers/suggestions on this one but I want
to emphasize one point because it is often overlooked.  The Radiator!!  I
had virtually identical problems with my '85, fought the problem for many
years, finally cost me an engine.  And all the time it was a clogged
radiator.
The bleeding of all air in the cooling system can get tricky on the 1.9L and
it's cooling system, make sure you are doing it right.
And the only sure way to tell if you are getting exhaust into the coolant it
to go to a shop that has a 'sniffer' and test with that.