All Focus thermostat housings will have problems eventually. Look around the drivers side of the engine. Most of the time, the valve cover will leak slightly and the oil will get into the housing and destroy the o-ring. This in turn will cause the housing to crack. You can also look on top of the transmission to see any signs of liquid. While you're checking under the hood, check the bottom of your overflow tank. They start to crack underneath also. Mine has had a small leak for a while. | 
