If a cooling system seems to be failing, it's often a mistake to immediately accuse the thermostat, though, because you should always consider the coolant level, the tension of the drivebelt, and whether the temperature gauge is functioning correctly either. Should the time it appears that the engine warm up requires by the operation of the heater or the temperature gauge be longer than normal, the thermostat is likely to be stuck open and therefore should be replaced. If the engine is hot, feel the upper radiator hose-if it does not feel hot while the engine is hot, then the thermostat is probably stuck shut and so the engine will need a new thermostat to allow coolant to flow out to the radiator. One must be particularly careful as driving without a thermostat may result in problems with the emissions and the fuel consumption. An upper radiator hose is hot when there is flow of coolant and the thermostat is open. Remove the negative battery terminal and then drain the cooling system, if the coolant is in good condition, you ought to save it. To access the thermostat housing you have to look for the upper radiator hose, slide it over the engine, undo the hose clip, and retract the hose. If the outer surface of the fitting is worn out, it may require replacement of thermostat housing cover. Take the bolts out and then disconnect the housing cover: be ready for some coolant loss. Before removing the old thermostat, you need to know its orientation and clean the faces of gasket well. Fit the new thermostat with the appropriate end upwards, through they should also align the air bleed holes. Coat both the sides of the new gasket with RTV sealant, fit it into the housing and then place the cover into the housing and screws the bolts up to recommended torque. With the engine off, reconnect the hose and secure the clamp, then add the missing coolant, and if you turn the engine on, you will be able to check for leaks, and or a properly working thermostat.