Maximize MerCruiser engine performance and efficiency by running at the optimum temperature A failed thermostat can cause an engine to run at outside of its optimum temperature adversely affect performance and efficiency. The fix can be as simple as replacing the thermostat. Sierra makes gathering the parts easy by packaging the thermostat with all the necessary components for an easy out the box installation. Kit includes thermostat and all necessary gaskets. For 50 years Sierra has been producing parts engineered to meet or exceed the specifications of marine engine manufacturers and has gained the confidence of engine manufacturers and boat builders. Boaters and technicians can be assured a Sierra part will fit right the first time and restore function to OEM specifications.