I have a daewoo nubira with no heat replaced thermostat and still no heat?

locate your heater hoses, start your engine and find the one that warms first, this is your " in" hose. Shut off your engine, disconnect both in and out hoses. You will now want to connect an air hose or water hose to the "out" hose and backflush you heater core until it runs clear. You can also use a product like CLR (calcium- lime-remover available at most stores) Fill the heater core with the CLR ( both hoses elevated above the core) for about 15 min. Then reflush you system and couple of times as you did in the first procedure , then reconnect the heater hoses to their proper outlets and fill with coolant. Run the engine, check for leaks and coolant level, you should have heat now, maybe not 100% but more than you had.