Engine must be cold, drain coolant, follow upper rad hose to engine and remove the housing. Clean old gasket from mating surfaces and place new gasket and thermostat. Be sure you put thermostat in proper way, check valve up and in the right direction. Tighten housing, put drain plug back and fill rad with a 50/50 mixture of water and coolant. Run car until warm, fans come on, check for leaks. Allow to cool completely and check level, adding if needed.