car is using lots of water but not overheating and heater does not blow hot air

You will need to locate where the coolant is going first. Fill system and pressure test to 20psi. Install 3/8"Tee into bleeder hose at reservoir and apply air pressure to test system including cap, otherwise you will need the special adapter. Common leaks are cracks in plastic reservoir. Radiator and hose connections. Water pump leaks (original at 85K to 100K) Aftermarket pumps fail sometimes as early as 30K. Plastic thermostat housings warp and start leaking. As for the heater, they plug easily and won't work well if coolant is low. Never put stop leak in these cars beause it will plug the heater core. Fix the leak instead.

replaced thermostat still no heat or defrost should i replace heater core next