sure you need to you can do it fast but you will need to add coolant and myu advice is to when you need to replace the thermostat its the time to replace the coolant
some
When changing the thermostat on a Nissan 300zx first drain the coolant from the engine. Then find the lower coolant hose on the radiator. Trace the hose to the thermostat housing. Remove the housing to uncover the thermostat and replace the unit with a new thermostat.
The water pump will pump coolant(antifreeze & water) through the engine after the thermostat opens up.
If the engine is overheating, the thermostat is stuck closed. If the heater is not putting out enough hot air the thermostat is stuck open. Change the thermostat as a normal part of maintenance when changing coolant.
The thermostat may be installed backwards
probably the heater core is clogged
"COOLANT THERMOSTAT" -COOLANT TEMP BELOW THERMOSTAT TEMPERATURE
If this happened immediately after changing the thermostat, then the most likely problem is the thermostat was installed backwards.The spring side of the thermostat faces the engine. It's the spring that is reacting to the coolant temperature and driving the valve to open/close.When the thermostat cannot open, that prevents any coolant from ever getting to the heater core. Thus, you shiver a lot!Pop it out, flip it over and you should be all sorts of warm and cozy.See "Related Questions" below for more
If this happened immediately after changing the thermostat, then the most likely problem is the thermostat was installed backwards.The spring side of the thermostat faces the engine. It's the spring that is reacting to the coolant temperature and driving the valve to open/close.When the thermostat cannot open, that prevents any coolant from ever getting to the heater core. Thus, you shiver a lot!Pop it out, flip it over and you should be all sorts of warm and cozy.
Spring side down always because it has to contact the coolant to open at right temp:-D
If there is not bleed valve for the coolant you will have to do it manually. Fill the radiator up and start the car. After it warms up the coolant level will drop, refill it.
try changing thermostat and a coolant flush if that doesn't work probably blown head gasket or cracked head or block. Could be, low on coolant, a stuck open thermostat, a plugged heater core or faulty temp blend door actuator.