there are alot of reasons it could be over heating.
in the old Tercels the electric fan that cools the radiator starts to wear which in turn starts to stick,
Start er up and check to see if the fan is working to full potential.
also your water pump may be failing. If it fails (pump bearings, clogs, etc)your thermostats temp goes up because coolant in the water jackets of the engine are being heated to boiling, but not being pumped through the rad to cool. Also check the tightness of your belts, if they are loose, your water pump may not work well. Have you added water without adding coolant? Try a hydrometer and check the strength of your rad fluid.
Also possible that head gasket could be bad. If you've done other things and still overheating. If your engine has got very hot in the past this could be your problem.With a aluminum head and cast Iron block these head gaskets can be blown very easily. If you run with this condition very long head damage will eventually occur.
If you know how to check all these things go for it, if not get it inspected.