i'm also haveing a heat delima, im heating up only when a/c is on or sitting still, 86 n/a gxl manuel 5 speed, radiator seems to leek a little when over heating only. every thing else seems to be working properly such as w/pump, f/ clutch, ect. please help,this is my third engine due to stuppidity

 

Do you have a fan shroud? Those are quite important. Maybe the viscous clutch in the fan is going out and the fan isnt pulling as much air as it should? What water/coolant ratio are you running? Living in a warmer climate you should do something close to 75% water/25% coolant and dump a bottle of Water Wetter in there.
Hope this helps some,
Tom

 

The list of things to check gets longer everytime I type it...*sigh* here we go again:

Thermostat - Replace with Mazda OEM only. (No pep-boys!)
Flush the Radiator - Use prestone super flush as per instructions.
After flush - Fill with 30% Antifreeze, 70% water

Do you have the underbelly pan installed under the engine? Yes you need it.
Is the fan shroud securly attached?
How old is the radiator cap? Replace it with Mazda OEM
Does the fan spin freely when the car is warm? You may need a new fan clutch.

That fact that your radiator leaks is also a bad thing. If the system can't hold pressure, then you will probably overheat.