The thermostat on a 1999 Kia Sportage is replace by removing the upper radiator hose, unbolting the thermostat housing, and removing the thermostat. A new gasket can then be put in place and a new thermostat installed.
You can view the 1999 Mercury Sable owners manual online at : www . motorcraft service . com ( no spaces ) Click on Owner Guides ( the fuses and relays section starts on page 119 , it has the diagrams and lists )