Heating troubles

Replaced the thermostat and it still runs hot. Radiator and hoses will be cool to touch but gauge read hot. The hose that connects to the block will be hot just a little past where it connects. Defrost blows cold air. I am putting gallon to gallon and a half of water in before I can drive it. It will go about 30 miles before it runs hot.If anyone can help I would appreciate it greatly. :banghead: