I have a 96 Nissan Sentra with a 1.6 liter engine and has 120k miles.
It recently began overheating and I had to turn on the interior heater
to drop the temperature down.   Since I do most of my own work on the
car, I have done done a number of things to resolve the problem...
but, with no luck so far.  I need some suggestions on what else I can
do.

Here is what I have done so far:

1.  Brought the radiator to the radiator repair guy in town.  He did
an informal flow test (put a hose in one opening and watched the
outflow out of the other).  He said that in his opinion the radiator
had sufficient flow.... surely enough flow so that it shouldn't have
caused the problem I experienced.

2.  Changed out the water pump and thermostat.   I decided with 120 k
miles on the car, I wanted to do this anyway.

3.  I checked the fluid in the radiator as the engine was warming up
and thought I saw bubbling.   Additionally, I saw signs of vapor
coming out of the tail pipe as I was starting up.    Lastly, it seemed
that my antifreeze levels had been coming down in recent weeks without
signs of obvious leakage.    All this convinced me that I must have a
blown head gasket.

I brought the head to a automotive machinist in town and his
estimation was that the head did not show signs of antifreeze leakage
in the head combustion area.    He indicated that the valve area of
the leakage would show obvious signs if such leakage occurred.

After all of this I am not sure what I should check out next.   I need
suggestions.    My first thought is that maybe I should change out the
radiator anyway just to eliminate that as a problem.    What do you
think??

Al Kondo