What would make a Mercury Cougar blow cold air and the temperature gauge to overheat?

Low coolant in system and heater core needs to be flushed or changed

AnswerThere could also be is (air pocket) air in the system. If motor is cool and resivoir is full. Fill radiator from upper radiator hose run till warm then re-check resivoir. AnswerClassic head gasket leak, (a bad one probably ) Answerone thing every one missed is the thermostat if the colant is full and the car is running good other than the cold air and over heating i would change the thermostat before i would the head gaskets, one way to check the thermstat is to start the car and let it run till the gauge gets to mid range, shut the engine off and feel your radiator if its cold your thermostat is bad, another method is to pull the thermostat it should be closed when its cold, put it in a pan of water and heat it to between 185 to 195 degrees using a thermometer to check the temp, once that temp is reached the thermostat should open if it does its good and if it does not than its bad. if its a head gasket it will show one of these signs, one of the biggest signs on a couger is white smoke out the tail pipe, wich is burning antifreeze, another sign is water in the oil wich will make the oil on the dipstick look brown and milky or white and milky, another is oil in the water wich if you look in the radiator there will be brown or black spots of oil. if any of these apear you have a blown head gasket,the other way you can check is to buy a compression tester and test each cylinder for the correct compression. Michael