it could be the water pump or a blown head gasket
Even though you have already replaced the thermostat, there are other issues that can cause your Nissan Maxima to overheat. Your fan may be stuck and not operating as it should.
water pump
Would need to know if car was overheating before waterpump and thermostat was replaced.
Maybe cooling line is plugged or crimped Maybe cooling tank in radiator is plugged Install auxilliary transmission cooler
Try flushing heater core Try flushing heater core
Could be several reasons but we really need to know the year, make and model of your vehicle to help you.
How did you change the thermostat?
Does that mean that you replaced the thermostat AND the sensor? If not, you really need to replace the thermostat. A sticking thermostat can cause temperature swings and potentially overheat the engine. BTW, BMW engines tend to have serious problems when they overheat. Don't let it overheat or you might be buying a new engine.
If you replaced some of theses already ignore and go down the line # Not enough coolant # Water pump drivebelt defective or out of adjustment # Radiator core blocked or grille restricted # Thermostat faulty # Electric cooling fans blades broken or cracked # Radiator cap not maintaining proper pressure # Ignition timing incorrect
flush out heater hoses
Head Gasket failure or intake gasket Dexcool is the culprit, had to replace mine.
Could be a head gasket or a warped or cracked Cylinder head.