Replacing a Thermostat in Your Car. Make sure your car has cooled down. Drain the antifreeze out of your car. Locate your thermostat. Remove the radiator hose and take apart the thermostat casing. If desired, test your thermostat. Swap out your old thermostat for the new one. Reassemble the system.
. Before you buy a replacement thermostat, however, take a peek at your existing wiring. If there are only two wires, the simplest solution is to get a replacement..