The thermostat in the 2000 Ford Focus works by opening a jiggle valve as the temperature of the radiator fluid rises. As the valve opens, the thermostat allows more fluid to flow through the radiator, thus cooling the fluid and the engine temperature down. Over time, engine buildup in the coolant system causes the thermostat to corrode. This corrosion causes the thermostat to fail. When this happens, the valve stays in the open position and reduces the engine temperature, thus reducing the amount of heat the Focus produces inside of the car. This means you must replace the thermostat in your 2000 Ford Focus.
Open the radiator drain plug by inserting a ¼-inch ratchet drive into the drain plug, then drain 2 gallons of radiator fluid into a drain pan. The plug loosens by turning the ratchet counterclockwise. Close the drain plug once you drain the fluid. This drops the fluid in the radiator below the height of the thermostat. This prevents fluid from draining from the radiator hose as you replace the fluid.
Locate the area on the top of the engine where the upper radiator hose connects. The hose connects to the thermostat housing. Remove the hose by loosening the band clamp with a screwdriver, then pull the hose off the thermostat cover.
Remove the two bolts that secure the thermostat housing to the Ford Focus with a 9/16-inch socket. Lift up on the housing to remove it from the engine.
Pull the old thermostat out of the intake manifold and then place the new one into the intake. The design of the thermostat allows it to fit into the intake in one manner.
Lift the old gasket off of the intake manifold and wipe the surface clean with a shop towel. Place the new thermostat gasket onto the intake.
Wipe the bottom of the thermostat housing clean with a shop towel and place it on top of the gasket. Tighten the thermostat housing in place with the old bolts.
Slide the hose onto the thermostat housing and secure it by tightening the band clamp with a screwdriver.
Open the radiator cap on the top of the radiator and drain the 2 gallons of fluid back into the Focus. Close the cap once you are finished.
