2000 toyota celica gts,no heat,overhe4ating,changed thermostat,same problem.not loosing any fluid n no water n oil

Hi, the indication is a possible blown head gasket. Such a leak can create an air bubble that hangs at the heater hose. To verify, park on an incline, open the radiator cap, run the engine until the thermostat is open, and fill the radiator to the neck. Wait until the level stops dropping and make sure bubbles don't continue to come up. If they do, you may have a blown head gasket that will keep forming these bubbles until you change the gasket. When the haed gasket causes overheating, it is usually leaking quite a bit of gasses into the coolant system. If this is not the problem, please see my tip at http://www.fixya.com/cars/r6235876-no_heat_fan_blowing_cold_air for additional troubleshooting steps. These are generic instructions. If you get stuck or need specific instructions for your car, please get back to me with model, year and engine info.