Have a 1990 1.5 Hatch completely stock. Overheats only when outside temp is warm and climbing hills. Fan working, new thermostat, no coolant loss, system bled, new radiator cap, great gas milage and runs fine otherwise. Cleaned outside of radiator to get rid of all the bugs.
Any ideas?

 

head gasket ? Radiator clogged inturnally ?

I had this problem kinda when it was hot out and I lugged the motor down the temp would rise and changed the radiator and fix it ....but it could be the head gasket. Or?

 

I am leaning toward internal radiator. It doesn't act like a bad head gasket or water pump

 

I'm having the same issue as well in my 92 LX. Changed everything you said and the radiator....still overheats...I'm about to replace the head gasket but there are no signs of a gasket leak(no white smoke, no bubbles in coolant, no coolant lost).

 

Probably internal, I have a radiator you can try if you in my area.